Soil, potting soil, compost and fertilizer

In this group of articles

Soil pH

Soil testing

Getting ready for planting

Choosing a good potting medium

Reusing potting soil

Types of fertilizer

The difference between soil, dirt, planting medium and compost

All About Soil pH

If you’re a gardener you have probably ran into the term soil pH.  It may be used in reference books or on plant tags.  But just what is soil pH and how important is it?  In this article we will discuss what gardeners need to know about soil pH.

What pH stands for

The term pH stands for the potential or percentage of Hydrogen ions in a solution.  (The correct way to write this term is lower case p, upper case H.)  In soil, the hydrogen ions are in the water that fills the pores between soil particles.  The more Hydrogen ions in a solution the more acidic it is.  

Soil is composed of minerals from dissolved and crushed rocks, and of organic matter, air and water.  The types of rocks that formed the soil in an area added different minerals to the soil.  Some of the minerals are beneficial to plants and some are not.  Hydrogen gets into soil from the rocks, from the breakdown of organic matter and from chemical reactions in plant root systems.  The more hydrogen in soil the more acidic it gets.   Different minerals in the soil dissolve and become available to plants at different levels of  pH.

A pH scale is a way to rate how acidic or alkaline soil is.  It ranges from 0-14.  Seven is considered neutral. Above 7 is alkaline and below 7 is acidic.  The pH increases or decreases by ten times for each point on the scale.  A pH of 6 is ten times more acidic than 7 and a pH of 5 is ten times that or one hundred times more acidic than a pH of seven.

So what does pH mean to gardeners?

How acidic or alkaline the water in soil is determines what kinds of mineral elements get dissolved and become available to plants or get bound up in complex reactions and become unavailable.  Most plants grow best at pH levels of 6.5 to 7.5.   That is where the most beneficial minerals become available to them.  A few plants have adapted to survive in pH levels slightly higher or lower than that.

In addition the pH level in soil also affects the microbes and micro-organisms that break down organic matter that adds nutrients to soil.  They like to grow at about the same pH level that plants do.

The soil your plants are in can have all the essential elements needed for producing food but if they are unavailable because of too high or too low pH the plants can’t use them and will suffer.  Certain plants are more sensitive to the loss of certain minerals such as iron.    When the pH of soil goes above 6.5, iron becomes largely unavailable to plants.   Some plants like Pin oaks will quickly decline.  In other cases the pH level may cause toxic elements, such as aluminum, to become too available to plants

In most areas a wide range of plants will grow, but your soil pH may determine whether or not some species will survive in your garden.  But just because plants will continue to survive doesn’t always mean all is well.  Marginal deficiencies caused by pH problems may cause your plants to become more susceptible to disease and insect attack because their immune systems aren’t as effective.

Pesticides may not work effectively if your soil pH is too high or low either.  They are developed for use in the pH range that most plants prefer.  The chemicals in them may react with elements available in too high or low pH conditions.

How do I find out my soil pH?

You can get your soil tested at almost any County Extension office in the United States.  Many garden and farm service stores also offer the service.  They will tell you how they want you to collect and submit the specimen.  These places will generally give you recommendations with the results for fertilizing or changing the soil pH.

There are small kits that have you mix water and soil and test the pH but these are not very reliable.  If you are a person who likes to do it yourself you can purchase a small meter that has probes that go into moist soil and reads the pH.  The more expensive ones used by professional growers are pretty accurate.

How do I change my soil pH ?

Soil pH can be raised much more easily than lowered.   If your results are only slightly out of optimum range and your plants seem to be growing well don’t worry too much.  Adding lots of organic matter and working it into the soil will help balance soil pH.  Lime can be added to soil that is too acidic to raise the pH.   This works fairly quickly.   Don’t add lime until you know your soil needs it and then follow the recommendations for your situation.  Soil may be acidic if it is too wet from poor drainage or lacking air from soil compaction.   Changing these conditions may help.

Lowering soil pH is harder and takes longer than raising it.   Too much lime or too many wood ashes can raise soil pH as can natural conditions.   Adding organic matter helps.  Fertilizers such as ammonium nitrate or ammonium sulfate will tend to lower pH.   These are often marketed as fertilizers for acid loving plants. If the drainage is good lots of rainwater or softened water may leach out some of the alkaline elements over time.

For small areas aluminum sulfate or sulfur can be tried.  You will need to consult with your county Extension office or other garden expert to find out how much to use on your soil.  This method will be quite expensive.

Choosing plants that like the soil pH you have in your yard is another good way to minimize plant stress, providing the soil pH is not too high or low.  There are plants that like both more acidic and more alkaline conditions.

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How to get your soil tested 

Every gardener has heard it- get your soil tested.  But many don’t know why they should do it, how to do it, or where they go to get it done.  Here’s the scoop on why, when, how, and where to get your soil tested in Michigan.

Michigan is blessed with a number of soil types.  Knowing what type of soil you have in your garden and the basic fertility of that soil lets you make important decisions on improving the soil and choosing plants that will do well in your soil.  You don’t want to spend money on fertilizers you don’t need and that may harm the environment.  And you certainly don’t want to buy expensive plants that aren’t likely to grow in your soil.

Gardeners should get a soil test when they are new to gardening in an area, when they have never had the soil tested or when they are experiencing a lot of problems growing plants.  After your initial baseline soil test it’s a good idea to test your soil every 3-4 years unless you suspect a problem and then you may want to do it sooner.

The most common soil test will tell you the basic soil composition, the pH (see this article on pH) of the soil and the amounts of potassium and phosphorus, major plant nutrients in the soil.  It will not tell you how much nitrogen is in the soil because nitrogen is constantly fluctuating.   You can also ask to have the percentage of organic matter tested. Soil labs can also test for micronutrients.

A normal garden soil test does not tell you if the soil is contaminated with chemicals like lead or pesticides.  This type of soil test can be done but it is expensive. 

You can get your soil tested at any time it isn’t frozen solid.  The spring planting season is a time when many home gardeners send their soil for testing but that is also the time when you will wait the longest to get results simply because the labs are so busy.  Fall is a good time to send soil for testing as is during a winter thaw when you can scoop out soil or very early spring and mid-summer.

How to collect a soil sample

The home gardener can simply dig down to 6-8 inches with a narrow spade.  Remove any large rocks and as much surface vegetation as possible and place the sample in a bucket.  Repeat this in 10- 20 locations across the garden spot.  Larger areas need more samples.

Combine all the samples by mixing the soil together well in the bucket.  Then remove 2-3 cups of soil from the bucket.  If the soil is very wet spread it on a newspaper in a warm spot and let it get as dry as possible before packing it up.  Place the sample in a zip close plastic bag.  

Most small suburban lots need to have only one representative soil sample taken.  But if you know the soil is different in different parts of your landscape, you have a large piece of property where you will be growing things in different areas, or you suspect a soil problem in one area you will want to do more than one sample.  Make sure you label the samples so you know where they came from.

Where to send your soil sample to be tested

In Michigan the primary soil test lab for homeowners and farmers is Michigan State University’s soil lab.  Some lawn care services and nurseries offer soil testing but most of them send the soil to MSU anyway.   There are some private labs that do soil testing but they generally concentrate on chemical contaminate testing or test soil for large farming operations.

Before MSU’s re-organization it was fairly easy to get a soil test done by going to your own county Extension office with your sample.  In some counties that is still being done.  They will help you fill out the paperwork, box your sample and send it for you.  But after MSU’s disorganization things aren’t that simple for all counties.

Call your local Extension office and ask about doing a soil sample.  They may tell you to send your own sample and how to do that or tell you they can do it.  If they do it they may sell you a sample box to fill or simply take your sample and fill the box for you, charging you one fee for the box and shipping.  Fees vary from $15 to $20 at county Extension offices.

At one point MSU was selling soil test kits through their bookstore but a recent chat with the soil lab at MSU reveals this is no longer being done.  Probably the simplest way for a homeowner to get a soil sample done is take the 2-3 cup sample collected and mail it yourself. 

First go on line and download the form you’ll need to send with the sample at this location   http://www.css.msu.edu/_pdf/SampleSubmissionForm4.pdf        Print it and fill it out.   Put each sample in a separate plastic bag with its own form attached.  Mark the form with a number or letter that corresponds to where the sample was taken from if you have more than one sample and keep a record for yourself.

You can put several properly labeled samples in one shipping box.  The post office sells one price shipping boxes you can purchase.  Enclose a check for the sample processing fees.  At this writing a common home garden soil test is $17, without organic matter testing. Add a dollar handling fee if you don’t have a proper soil test box from MSU for a total of $18 per sample.  Your shipping cost is extra, paid at the post office.

On the same webpage where you downloaded the submission form the MSU soil lab has a fee list.  If you want the organic matter in your soil tested add the correct amount.  It’s a wise idea to consult the fee list before writing your check as MSU has announced they will soon be changing the test fees.  They are going to make the organic matter test standard at some point in time and raise the test fee to reflect that.

If you have questions call the soil lab at (517) 355-0218

Send your soil sample to this address;

            Soil and Plant Nutrient Laboratory
            A81 Plant and Soil Sciences
            Department of Crop and Soil Sciences
            Michigan State University
            East Lansing, Michigan 48824-1325

You can drop off the soil sample during business hours if you live close to East Lansing and that will save you postage.  For a map go here http://maps.msu.edu/files/driving.pdf

Expect your results in about 2 weeks, a little longer during spring rush.  A report will be mailed to you with your results and recommendations for soil improvement. A link to a webpage with explanations for what MSU recommends will also be sent.  If you are lucky your local Extension office may still have someone who can help you interpret your results.

A simple amendment to change the pH of your soil if needed, the correct amount of fertilizer to add to the soil and knowing your soil type will help make you a super gardener.  And you get this information from your soil test.  A soil test is worth the time and money.

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How to get your soil ready for planting

A healthy garden requires healthy soil.  Healthy soil creates disease and insect resistant plants. Soil is the earth beneath our feet.  It’s a mixture of rock broken into small particles, decayed organic matter and pore spaces, some filled with water, some with air.  Soil may also contain a lot of living organisms, many too small to see, such as bacteria and fungi and larger organisms such as grubs and worms.

Soil varies from place to place depending on what rocks were broken down to form it, how fine the rock particles are and what organic matter has been added to the mixture.  What we call clay is rock broken down into the smallest particle sizes, with small pores for water and air. Sand has the largest rock particles and pores. 

The organic matter in soil is called humus.  It has finished decaying and is a fairly stable product.  The organic matter in soil and the minerals that came from the rocks broken down in the soil determine the soil pH and the nutrients available for plant growth.   They also determine the color of soil.   Soil color varies from light brown to almost black.

The mixture of rock particles and humus leads to different kinds of soil.  A soil heavy in humus with fairly even amounts of clay and sand is called a loam soil.   A soil with a little more clay is called clay loam and so on.  In nature plants will grow in the type of soil they prefer and each kind of soil has advantages and disadvantages.  When we want to grow certain types of plants in areas where the kind of soil isn’t suitable we need to amend it.

Top soil is the layer of soil closest to the surface and that soil generally has more organic matter or humus, therefore it looks darker.  Soil isn’t “better” because it is dark in color, nutrient rich soils can be light in color.  Be careful if you buy topsoil, it is generally collected from building sites or waste areas and can be filled with debris, weed seeds, and even dangerous chemicals.

 Any type of soil can be improved by generous amounts of organic matter.  It may take several years to develop good soil, but you can work on it each year as your garden grows. Organic matter includes things like manure, leaves, lawn clippings, compost, straw, and even shredded newspaper.  You can start the garden in the fall, by layering lots of organic matter on the garden site.  You continue by adding more organic material in the spring and mulching around the plants with organic material.

A foot of organic material on the garden in the fall and several inches in the spring and around plants in the summer is excellent.   As the organic matter is broken down add more.  Organic matter that is in the process of breaking down will use some nutrients, especially nitrogen.  However, it will eventually add nutrients to the soil.

Getting a soil test

Gardeners should get a soil test when they are new to gardening in an area, when they have never had the soil tested or when they are experiencing a lot of problems growing plants.  After your initial baseline soil test it’s a good idea to test your soil every 3-4 years unless you suspect a problem and then you may want to do it sooner.

The most common soil test will tell you the basic soil composition, the pH of the soil ( acidity and alkalinity), and the amounts of potassium and phosphorus, major plant nutrients in the soil.  It will not tell you how much nitrogen is in the soil because nitrogen is constantly fluctuating.   You can also ask to have the percentage of organic matter tested. Soil labs can also test for micronutrients.

A normal garden soil test does not tell you if the soil is contaminated with chemicals like lead or pesticides.  This type of soil test can be done but it is expensive. 

How to collect a soil sample

The home gardener can simply dig down to 6-8 inches with a narrow spade.  Remove any large rocks and as much surface vegetation as possible and place the sample in a bucket.  Repeat this in 10- 20 locations across the garden spot.  Larger areas need more samples.

Combine all the samples by mixing the soil together well in the bucket.  Then remove 2-3 cups of soil from the bucket.  If the soil is very wet spread it on a newspaper in a warm spot and let it get as dry as possible before packing it up.  Place the sample in a zip close plastic bag.  

Most small suburban lots need to have only one representative soil sample taken.  But if you know the soil is different in different parts of your landscape, you have a large piece of property where you will be growing things in different areas, or you suspect a soil problem in one area you will want to do more than one sample.  Make sure you label the samples so you know where they came from.

First go on line and download the form you’ll need to send with the sample at this location   http://www.css.msu.edu/_pdf/SampleSubmissionForm4.pdf   Print it and fill it out.   Put each sample in a separate plastic bag with its own form attached.  Mark the form with a number or letter that corresponds to where the sample was taken from if you have more than one sample and keep a record for yourself.

Do you need fertilizer?

Plants manufacture their own food by photosynthesis so it is technically wrong to call fertilizer plant food.   But in order to manufacture their food plants need certain elements from the soil.  Different types of plants use elements in different amounts.   When the same plants grow in the same spot for a long time the elements they need may become depleted, which leads to poor plant growth.

It is important to have a soil test done before fertilizing and also to learn about the plants you have in your garden to see if they have special needs.  Too much fertilizer is bad for the plants and bad for the environment.   Many perennial flower plants only require a small amount of fertilizer in the spring.  Annual flowers, however, need frequent small doses of fertilizer.  Fruit trees and plants need fertilization in the spring.  Ornamental trees and shrubs may or may not need fertilization depending on the species and your soil.

Some plants do better without extra fertilization, they are generally plants that evolved in places with poor soil and are very efficient in using what is available.  When we give them fertilizer they may grow differently then we expect and are more prone to disease. Other plants may have a high requirement for certain elements in smaller quantities in soil, called trace elements.   

Vegetable gardens generally need some fertilizer, whether organic or not each year. Sources of nutrients for organic vegetable gardens include manure, bone and blood meal, fish and feather meal, alfalfa hay, cottonseed meal and seaweeds.  Bone, fish and blood meal may actually attract some pests to the garden, such as raccoons. Some of these things are easy to find locally and some are not.   There are now organic bagged fertilizers on the market.  While they are easy to use they don’t add organic matter to the soil as natural sources often do.

Manure is often thought of as fertilizer.  Manure can vary tremendously in its nutrient value depending on what kind of animal it came from, what the animals were fed, and how long and where it was stored.   Manure may also bring weed seeds to the garden.  Fresh manure can cause chemical burns to plants, and manure should be aged for several weeks before applying to the garden during the gardening season.  Avoid adding manure to vegetable gardens in the spring to prevent food borne illness.   Never add human or dog and cat manure to the garden as it may be the source of parasites and diseases. 

To add commercial fertilizer to the soil follow the package directions for the amount.  Most granular fertilizers should be lightly worked into the soil before planting.  You can do this with a rake or if you are tilling add the fertilizer to the soil surface first.  Choose a fertilizer that is listed on the label as suitable for the plants you want to grow.  If you had a soil test done it will give you recommendations for fertilizer.

To till or not to till

It’s the season when many people are itching to get out the rototiller.   The only time a rototiller is necessary in a garden is for maybe the first time the area is used for a garden, especially if the soil is compacted, or if you need to mix a lot of organic material into it to make it useable.  You can even skip the rototiller the first time if you have the forethought to smother the turf and weeds from a piece of ground the season before you want to garden on it.

Good soil is a living thing, full of thousands of tiny living creatures from bacteria to worms.  All of these creatures have important roles in creating good soil.  They all have their own “comfort zones” in the soil, some at the top, some at the middle and some deep in the soil where they perform at peak efficiency.   Every time you rototill the soil you disturb these amazing critters, throwing them out of their best levels of efficiency and even killing them.

Rototilling also brings weed seeds to the surface where they can germinate.  The seeds of some weeds can lay in the soil for years until a rototiller or spade moves them close to the surface for light and warmth to germinate.  Weed problems are often worse when you rototill every year.

Rototilling destroys soil structure.  Good soil is actually small clumps of minerals, organic matter, and water bound together by a bacterial “glue”.  Tilling the soil so that these clumps are broken apart makes your soil much less suitable for plant growth.  While you don’t want rocks or huge clumps of soil in a garden bed, you also do not want soil the texture of flour.  To take the cooking analogy further, your soil should look like crushed Oreo cookies, not flour. 

Finally tilling tends to compact the soil just beyond the depth of the tiller tines.  If your tiller blades reach 8” into the soil it’s probably compacted at 9”.   So how do you get deep, rich, loose soil?  By making dedicated beds and paths in your garden and never walking on the beds.  You can make these raised beds or not as long as they are well defined.  You pull weeds or use a hoe to remove them and use mulch and you add lots of organic matter each year.  Each year in the spring simply remove any sprouting weeds, add some well-rotted compost to the beds and plant.

Using rock powders in the garden

If you have ever gardened in pure compost, or other pure organic material, you may have wondered why your plants didn’t grow as well as you thought they would.  That’s because good soil also contains minerals, or crushed rock.  Plants need minerals to grow properly.  You can add minerals with fertilizer and we know that with the right balance of minerals plants can even be grown in water. 

If you have highly organic soil that’s a good thing, but you may want to consider adding some “rock powders” to increase the mineral content of the soil and make your garden soil even greater.  Everyone is aware of one rock powder, limestone, but that’s a mineral you want to add only after a soil test because it can make your soil so alkaline that plants won’t grow properly.  If your soil is too acidic, below 6 on the pH scale, you may be advised to add some lime.

Other rock powders are available that can be added to soil in reasonable amounts, about 40 pounds to a 1,000 square feet, and will be beneficial to most soils, especially clay soils that tend to pack.  Here are some rock soils you may want to consider.  Greensand is just that, a sand like material that is green in color.  It’s mined from sea and lake sediments and the green color comes from the many minerals it contains.  It’s usually high in iron, magnesium and potassium.   Crushed granite and crushed lava stone are also high in minerals and they add pore spaces to soil that tends to pack, making it hold air and water in a better structure for plant roots.

What is Compost

Compost is simply organic material, anything that was once living, that has been broken down by microbes into a substance very similar in looks to fluffy soil.   Nature makes compost all the time; it’s called rotting when nature does it.  Leaves rot, a fallen tree rots, and apples on the ground rot.  Basically when you do home composting you want your yard waste and home garbage to rot.  

Compost is not fertilizer, although it does return nutrients to the soil.  It is not soil, soil has a base of broken down rock with organic matter added.   Eventually the fluffy material you produce from home composting will disappear, rotting down to pieces so small that it mixes with the soil, a very desirable thing.

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Choosing a good potting or seed starting soil

Choosing a good deed starting medium or a good medium to transfer seedlings into can be important to your success when you start seeds indoors.  For a seed starter you want a mix that does not contain any real soil, to avoid bringing in disease organisms such as dampening off wilt.   It should also be a fine textured mix, without large particles but it should take up water readily.  Seed starting mixes don’t need fertilizer; seedlings won’t need fertilizer until several pairs of true leaves have developed.  However if  you intend to leave the seeds in the containers for a few weeks you may want to use a mix with fertilizer, otherwise you’ll have to add fertilizer as the plants grow.   A new trend is to mix in soil microbes and mycorrhizae that are found in nature and that are beneficial to plant growth.

  

For transplanting seedlings, starting cuttings and repotting plants you need a light weight, moisture retaining mixture.  It can be a bit coarser than seed starting mix, the larger particles in this soil aid drainage and aeration of the soil. It’s best to transplant seedlings after they have two sets of true leaves into separate pots if you started them in flats or sowed multiple seeds in pots. (Or thin pots to one plant by cutting off all but one seedling.)   Some transplanting mediums have fertilizer mixed in; some will need to have it added.  While plants can manufacture their food they need certain minerals found in soil to do well, which you provide with fertilizer.  Some seed and transplanting mixes also have wetting agents, products that allow the soil to take in and hold more water.  And many now have soil mycorrhizae added.

There is an abundance of seed starting and transplant/potting mediums on the market and it can be hard to decide which one to purchase.  To add to the confusion some companies have a variety of places making their brand name mixes and each place can make a slightly different mix depending on local resources. One bag of the mix may not look or perform as well as another of the same brand.

Most commercial potting mixes/seed starters are composed of sphagnum peat, other forms of peat, perlite, ground bark or coir, vermiculite, limestone and various wetting agents, some have worm castings or mycorrhizae added.  So which brand is best?

There’s a rating below of what this author likes and dislikes about some common brands of potting soil.  To be completely fair the author received samples of Gardeners Supply and Miracle Grow potting soil for testing.  Other brands were purchased for comparison.  The author has used all of these soils.  There are many other brands of potting mix/ seed starting soil on the market and although they aren’t listed here it doesn’t mean they aren’t good mixes.

Gardener’s Supply Planting mixes/seed starter- I love both of these mixtures, seed starting and transplant mix.  They are lightweight, the seed starter is fine textured, and they both hold water well.   Plants grew very well in both mixtures.  These mixtures contain soil mycorrhizae and are pH balanced. (Soil mycorrhizae help plant roots process nutrients and get plants off to a fast start.) The mixes are very similar to Pro-Mix, an advantage is that you can buy this soil in smaller quantities than Pro-Mix and the cost is quite reasonable.   Gardener’s Supply offers discounts for multiple bags too. Cost is about $8 for a 9 qt. seed starting mix and $19 for 30 qt. transplant mix.  Gardener’s Supply offers an organic seed starter too, (which this author did not try). 

Pro-Mix- if you are going to be starting tons of seeds or transplants this is probably the gold standard.  Pro Mix is light weight and contains both mycorrhizae and a natural bio-fungicide. It holds water very well and is a delight to use.  It does not contain fertilizer. The disadvantage is that Pro-Mix comes in large, 3.2 compressed bales that weigh about 70 pounds.  It can be hard to find locally and shipping is very expensive.   You can store potting mixes from season to season but be aware that soil mycorrhizae can die over long storage and you will lose that advantage.  Cost ranges from $25 a bale up to $65, depending on where you buy it, and discounts are normally offered for multiple bales.  Remember to factor in shipping costs if it is shipped to you.

Espoma planting mixes- have the same ingredients as most potting mediums.  However they add worm castings which are said to have some nutritional benefits, along with mycorrhizae.  There are organic formulas too.  They are good mixes, light and water retentive but this author found no advantage over Pro-Mix or Gardeners Supply mixes. Prices are all over the place, the author found Walmart had the cheapest price, at about $10 for a 16 qt. bag.  Other places sell the same bag for about twice that.

Miracle Grow- the Miracle Grow brand name is well known but their potting soil mixes are known for variability, depending on where they are manufactured.  The company deems to be phasing out the seed starting mix.  Some mixes seem fine, lightweight and with good water retention.  Others have large pieces of coarse wood, sticks and other debris in them.  Some feel heavy and dense.  The author has had bags which were great in texture and others not so good.  All Miracle Grow mixes have fertilizer mixed in, which some growers don’t like.  It’s usually a bit more expensive than other brands; the author found it cost about $10 per 8 qt. bag, although specials and discounts seem frequent.  The soil seems to be fine for filling outside planters and large pots.

Jiffy potting mixes- not terrible but so-so, average in weight, texture and water retention.  They do not contain mycorrhizae and seem overpriced compared to other mixes.  The price the author found was about $19 for a 16 qt. bag.  The organic option was terribly expensive at $40 for 12 qt.

Hoffman potting mixes- typical composition, the author did not try it this year but has used the potting mix in the past with few problems.   Its pH balanced, seems to be a fine texture and holds water reasonably well.  It runs about $13 for a 10 qt. bag.

The author believes the small grower will be happiest with Gardeners Supply transplant or seed starting soil.  If you grow a lot of plants and can find it locally Pro-Mix is probably the best choice.

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Can you re-use potting soil from last years containers?

This time of year a gardeners thoughts turn to planting and many gardeners will be planting in containers that they used the previous year.  A common gardening question is can I re-use the potting soil left in the containers this year?  The answer is yes in most cases but you must do some things to make the potting mix suitable for growing healthy plants this year. 

If you had disease problems in your container plants last year and intend to grow the same type of plants in the container this year you should probably remove all of the potting mixture and replace it with new.  If the potting mixture became crusted and hard or didn’t seem to drain well it’s also time to replace it or at least amend it with a better planting mix.  However, most of the time the potting mixture in containers can be reused with some attention to details.

Plants growing in the ground can take up minerals from the soil which they need for proper growth. Soil is a mixture of broken down rocks (minerals) and organic materials. While plants can manufacture their own food from photosynthesizing, they do need some minerals, amounts and types needed vary from plant species to plant species, to properly carry out all their life functions. Most potting mixes contain no mineral soil, unlike the natural soil in your yard.  Instead the potting soil sold in stores is generally composed of peat, perlite, and some other form of organic matter such as ground bark or coconut fiber.  Some mixes also have water retaining granules added and many mixtures contain fertilizers.  These potting mediums are for anchoring plant root systems and if they don’t say they have a complete fertilizer included, they don’t meet all of the plant’s needs.

If the potting soil mixture in your container contained fertilizer last year or you added fertilizer to the mixture, it has probably been depleted by the plants that grew in it last year.  This is especially true of nitrogen, a nutrient greatly needed by plants but which also disappears into the air over time, as well as being used up by plants.  Other major nutrients needed by plants are potassium and phosphorus but plants also need trace minerals like copper, zinc and magnesium.  Most fertilizers can supply these needs.

If you are re-using potting mixtures from previous years you’ll need to re-new the nutrient content of the mixture.  The best way to do this is by mixing in some granular, slow release garden fertilizer found in all garden stores.  There are organic and inorganic fertilizers but plants don’t care which type they receive, it’s the human caretaker who takes that stand.  For flowering or foliage containers select a fertilizer for flowers.  If you will be growing vegetables in containers select a vegetable fertilizer.

What about liquid fertilizers?

Garden centers recommend you use liquid fertilizers once a week or so, on most flowering plants.  You should do that if you bring home a hanging basket or pre-planted container and leave the plants in it. And if you want you can skip the slow release dry fertilizer mentioned above and use liquid fertilizers on your containers on a regular basis.  Be very careful not to make the liquid fertilizer too strong, the roots of container plants can easily be burnt by strong mixtures. 

If you use a slow release fertilizer in containers don’t use liquid fertilizers on the plants for at least two months, or the plants may get too much of a good thing.  Most directions on slow release fertilizers claim they are good for 3 months and that will cover most of the growing season.  Some heavily blooming plants may need a little supplementation at about 2 months, especially if they have to be frequently watered, as this leaches out some of the minerals.

How to do it

The easiest way to re-new your potting soil mixture is to remove it from the container and place it in a large bucket or maybe a garden cart. If the container is large you can just remove the top 8 inches of potting mix for renewal. The planting medium from several containers can be dumped into one mixing container and renewed at the same time.  Stir up the mixture, breaking up clumps and removing any leftover plant debris.  Estimate how much potting mix you have and then mix in the proper amount of fertilizer granules by reading the label directions. Mix in the fertilizer thoroughly with a shovel or your hands.  Now refill your containers.

If you have just one container to renew you can probably dig up and loosen the old potting medium and work the proper amount of fertilizer into the container.  It’s always better to mix in the fertilizer before adding plants to containers.

If the planting mixture you used last year seemed to dry out quickly you may want to mix in some moisture retaining granules you can buy in stores or use the gel granules and absorbent material from the liner of a diaper.  You can also add some sphagnum peat or good compost to increase moisture holding capabilities and make the potting mix lighter. 

Since potting medium is lost when containers get knocked over, when it washes out through the drainage holes and when it sticks to plant root systems that were discarded, you may need to purchase some additional planting medium this year to fill your containers.  You can mix it with the old medium or choose one or two containers and fill them with the new planting medium, using the old potting medium in them in your renewal pile.  Many gardeners with a lot of containers to fill add some new potting medium each year.

Moisten all potting mixtures before putting them back into containers. You may need to stir it well to get water into the bottom part of the mixture. The mixture should look and feel moist but water should not seep through your fingers if you pick up a handful of the mix. If you put dry potting medium in a pot and then add water some of the mixture may float up and out of the pot.  The bottom layers of the pot may not get moistened and will suck water away from newly planted plant roots.

Adding garden soil and/or compost to containers

If you have access to good compost or you have loamy, light garden soil you could use it in your outdoor containers. Remember that compost is not fertilizer, and it’s not a good source of all nutrients plants need, so it will need a slow release garden fertilizer mixed into it for container plants to grow well.  Garden soil isn’t necessarily well balanced soil, and unless you have it tested it’s a good idea to use fertilizer in it also. Even a good garden soil will be depleted of some minerals after a year of plants growing in it and should be renewed with fertilizer. 

Heavy clay soil is not recommended for containers.  Not only does it make the containers very hard to move around, it tends to get like a brick when it dries out and when conditions are wet it may not drain well and plant roots will rot. You could mix clay soil with compost or peat, ground bark and so on- but it’s probably easier to just buy potting mixture.

If you bring plants inside for the winter garden soil is more likely to harbor creatures like worms and ants, although they can get in soilless planting mixes too. If this bothers you don’t use garden soil in house bound containers.

So yes, you can save money by reusing last year’s potting mix.  Just remember to fertilize container plants so you meet all their needs and keep them healthy and pretty.

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Types of Fertilizers for  Garden and Lawn Care

Do you need to fertilize your plants?  When a homeowner walks into the garden department of the local store he or she is often confronted with a long row of bagged fertilizers.  It seems like a daunting task to pick the type of fertilizer that will be best for your situation.  And some people are confused about organic matter and compost and their relationship to fertilizer.

Fertilizer and compost or organic matter are both good for gardens and you don’t have to choose one over the other.  In fact the best gardeners use both.  Compost and organic matter worked into soil improve your soil, helping it hold water and nutrients and making it comfortable for plant roots.  Organic matter and compost help supply soil organisms like bacteria that are beneficial to plant growth.  But compost and various types of organic matter may not supply some nutrients missing in your soil.

Plants manufacture their own food by photosynthesis so it is technically wrong to call fertilizer plant food.   But in order to manufacture their food plants need certain elements from the soil. The type of rocks that were broken down and the decayed organic matter in an area determine the type of soil that area has and the amount of essential minerals and other nutrients the soil holds.  Something will grow in almost any soil but it may not be good soil for what you want to grow.  And nutrients can be depleted from soil by plants or from water leaching them out of the soil.

The type of rocks that broke down in an area to form soil also determine the soil pH or it’s alkalinity or acidity. (Other things that happened to soil in an area such as the long use of certain fertilizers can also affect soil pH.) Sometimes all the elements necessary for plant growth can be in the soil but plants can’t use them because the pH level determines whether plants can take those nutrients from the soil.  

Do you need fertilizer?

Different types of plants use soil nutrients in different amounts.   When the same plants grow in the same spot for a long time the elements they need may become depleted, which leads to poor plant growth.  While nitrogen may be returned to soil from the air and decomposition of organic matter some other soil elements are not replenished naturally. 

Chances are good that vegetable gardens and plantings of annual flowers need fertilization.  These plants use soil elements up quickly and because they grow rapidly need fertilization. Roses generally need fertilization.  Lawns may need some fertilization, especially in fall to promote good root growth.  Fruit trees and things like strawberries and grapes generally need some fertilization to perform at their best.

Some plants do better without extra fertilization, they are generally plants that evolved in places with poor soil and are very efficient in using what is available. Some perennials and herbs fall into this category.  When given fertilizer they may grow differently than expected  and are more prone to disease. Other plants may have a high requirement for certain elements, called trace elements for good growth.   

It’s important to know the species of plants you grow as perennials, trees and shrubs in the landscape and what their needs are for fertilization.  Most references will give guidelines for fertilizing common plants.  Some plants like acidic conditions such as blueberries, azaleas and holly.  Using an acidic type of fertilizer helps them grow.  When a plant is said to be a “heavy feeder” it generally will need extra fertilization.

Too much fertilizer is bad for the plants and bad for the environment. You can always give plants more fertilizer but if you over fertilize plants you may burn the roots, cause leggy, weak growth, and more pest problems.  Having a soil test done every few years will let you know what elements may be needed in your soil.  Plants that are growing well, especially things like trees and shrubs, may not need fertilization every year.

Types of Fertilizers

Most fertilizers are made of synthetic ingredients.  The plants use these ingredients just as they do the elements found in nature. It’s no different than you using a vitamin pill instead of consuming foods with the vitamins and minerals you need.   Most modern fertilizers release elements slowly, over a long period of time.  Slow release fertilizers are less likely to burn plants but try to keep them off leaves and apply only as directed.

Some fertilizers are still quick release, which means the nutrients are all available at once.  This means a quick green up but less margin for error in applying before the plants are chemically burnt.  They must be applied more frequently than slow release fertilizers. 

Liquid fertilizers also give plants nutrients immediately.   Liquid fertilizers must be mixed and applied frequently.   Liquid fertilizers are good for container plants but difficult to use on large gardens and lawns.

There are fertilizers formulated for certain plants, such as tomatoes or roses.  These contain the major ingredients found in all fertilizers and also certain trace elements those plants are known to need.  If you have problems with a certain type of plant these may help.

Organic fertilizers are things like bone meal, blood meal, and manure. Organic fertilizers sold in stores should have the same labels as other fertilizers.   Most are high in one nutrient only and you may need to buy a combination of things.  New organic fertilizers with more balanced ingredients are also on the market. 

Some people also fertilize with fresh manure or compost.  Both are great for adding organic matter to the soil but used as a fertilizer they have drawbacks.  Manure and compost vary greatly in nutrient content from batch to batch.   You need a great volume of manure or compost, six or more inches, to equal a sprinkling of slow release fertilizer.  Fresh manure can burn plants and it can be the source of food borne illness if used on food plants.  Manure may also bring weed seeds to the garden and is hard to spread on lawns.

Choosing and using fertilizer

All fertilizer bags are required by law to have several things on the bag.  They must have three numbers on the bag or container.   These numbers signify how many pounds of the major elements plants need, nitrogen, phosphorus and potassium, in that order, are in the bag.  Nitrogen is first because it is the most important element for plant growth.  Phosphorus in fertilizer is banned in some states such as Michigan because it pollutes water so that place will be represented by a 0.

Fertilizer bags must have a list of active ingredients, the weight of the bag and instructions for proper use.  If there are pesticides in the fertilizer, such as a weed killer, the pesticide name and the pesticide registration number must also be on the bag.

The three numbers on the bag are based on 100 pounds of fertilizer.  A bag marked 15-20-15 would have 15 pounds of nitrogen, 20 pounds of phosphorus and 15 pounds of potassium per 100 pounds of fertilizer.  If the bag was a 50 pound bag then you would have about seven and a half pounds of nitrogen, (and half the other minerals), in that bag.  The rest of the weight would be made up of fillers, micronutrients, pesticides or other things.

Most fertilizers are also labeled garden fertilizer, lawn fertilizer, flower fertilizer etc.   These have different ratios of the major ingredients.  These are the easiest fertilizers for gardeners to use.  Just choose the fertilizer for the type of plants you are growing and follow directions.   Flowers and vegetables can generally use the same fertilizer, but lawn fertilizer is too high in nitrogen for vegetables and flowers. 

It is possible to buy fertilizer ingredients like phosphorus separately at farm supply stores but they are sold in large bags that would take home gardeners many years to use.  Buy only the amount of fertilizer you can use in one year.  Only buy and use phosphorus if a soil test indicates your soil is deficient in it.

Some fertilizers have weed killers or insect killers added to them.   Read the label carefully and follow directions exactly when applying these.  Never use weed killing lawn fertilizers on gardens or flower beds.  These kill broad leaved plants, which are also the plants in your garden and flower beds.  After applying these products keep children and pets away for the time recommended on the bag.

When to apply fertilizer

Apply slow release fertilizers to vegetables and annual beds at planting time.  You may need additional applications in mid- summer.  Most trees, shrubs, fruit plants and perennials should be fertilized in early spring.  Do not give these plants fertilizer in late summer or fall as it may make them more susceptible to winter injury. 

Mix in slow release fertilizers when planting containers or use a weak liquid fertilizer on them weekly.  Lawns do well with an early spring and early fall application of fertilizer.

The fertilizers that home owners use are a major source of water pollution.  Don’t get fertilizer on hard surfaces like sidewalks where it washes off into storm drains.  Always follow label directions for the amount and way to apply the fertilizer.

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Whats the difference between soil, dirt, compost, and planting medium?

Gardeners have a lingo all their own, just as most hobbies and occupations do. But knowing the difference between, soil, dirt,compost and planting medium isn’t just about lingo, or words, its about knowing what’s best for your plants.

Soil is the earth beneath our feet. It’s a mixture of rock broken into small particles, decayed organic matter and pore spaces, some filled with water, some with air. Soil may also contain living organisms, many too small to see, such as bacteria and fungi and larger organisms such as grubs and worms.

Soil varies from place to place depending on what rocks were broken down to form it, how fine the rock particles are and what organic matter has been added to the mixture. What we call clay is rock broken down into the smallest particle sizes, with small pores for water and air. Sand has the largest rock particles and pores.

The organic matter in soil is called humus. It has finished decaying and is a fairly stable product. The organic matter in soil and the minerals that came from the rocks broken down in the soil determine the soil pH and the nutrients available for plant growth. They also determine the color of soil. Soil color varies from light brown to almost black.

The mixture of rock particles and humus leads to different kinds of soil. A soil heavy in humus with fairly even amounts of clay and sand is called a loam soil. A soil with a little more clay is called clay loam and so on. In nature plants will grow in the type of soil they prefer and each kind of soil has advantages and disadvantages. When we want to grow certain types of plants in areas where the kind of soil isn’t suitable we need to amend it.

Top soil is the layer of soil closest to the surface and that soil generally has more organic matter or humus, therefore it looks darker. Soil isn’t “better” because it is dark in color, nutrient rich soils can be light in color. Be careful if you buy topsoil, it is generally collected from building sites or waste areas and can be filled with debris, weed seeds, and even dangerous chemicals.

Planting medium, potting medium or sometimes it’s called potting soil, really isn’t soil at all because it lacks the broken rock component of real soil. It’s usually composed of peat, shredded bark and vermiculite or perlite. Other products are sometimes used. Fertilizer- minerals- are usually added to these mixtures although one must read the bag label to find out.

Plants can grow for a while in soil-less mixtures like this without fertilizers because plants have the ability to make their own food. But eventually they do need some of the minerals that real soil has and that is furnished with the various plant “foods” or fertilizers that are on the market.

Sterile potting mediums are great for starting seeds and rooting cuttings to help avoid diseases that can be present in real soil. Not all planting mediums are sterile, so once again check the label if you need disease free medium for starting plants. Potting mediums are used in general for pots, hanging baskets and raised beds because they are lightweight, hold moisture well, are easy for plant roots to penetrate and don’t crust over and crack when dry.

Compost is organic matter that has decayed to a point where it looks like rich brown crumbles. It may have a few pieces of stem or larger matter still recognizable but most of what went into it should no longer be distinguishable. Compost has nitrogen and a number of micro nutrients plus helpful bacteria and other organisms in it. However the nutrient values of compost varies and it shouldn’t be considered fertilizer. Plants can be started in compost if it is sterilized and it can be used in hanging baskets and pots. Remember it has no broken down rock or minerals in it and those things will have to be added to make compost a good growing mix.

Compost is added to soil in the garden to improve it, to add nutrients and microorganisms, to make it lighter and hold more water. Compost eventually turns to humus. It would be very hard to add too much compost to any kind of garden soil.

A new bagged product on the market is called garden soil. It’s generally a mix of compost, soil from somewhere and maybe some peat. It is often used to fill raised garden beds. It’s more expensive than amending most garden soils but some people prefer the convenience.

Dirt is something we sweep out the door, dirt is debris, something undesirable. A good gardener learns to call the substance we grow plants in soil, planting medium or earth.

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What you need to know about seed starting soil or medium

As we near spring the gardeners thoughts turn to growing things and many gardeners decide to start some seeds indoors, to have plants ready to go when the weather conditions are right.  If you are going to spend a lot of money on seeds or have precious saved seeds you want to start, you need to know what type of seed starting soil will be best for your investment of time and money.

Before we go further, let’s get some terminology straightened out.  Most “soil” you purchase doesn’t contain any real soil- which is earth with a mineral base that is found in nature.  Rather it is a mixture of several organic ingredients such as peat, vermiculite, shredded bark and other things.  That’s because real soil is heavy, tends to turn into a hard brick when bagged, and each batch would be different, even if the soil was collected from the same area.  What is sold in stores for planting and starting seeds is properly called planting medium or planting mix.

The thing that you don’t want to do is use soil or compost from outside or to use soil you have recycled from containers other plants have grown in to start seeds.  You don’t want to use real soil sold in garden centers as topsoil either.  This is because seedlings are very susceptible to a fungal disease called “dampening off” and outside soil or soil that plants have grown in is likely to carry the fungal spores and infect your new seedlings.  It can also carry other diseases and insects that can harm your seedlings.

Planting mediums vary from company to company and different formulas are available for different types of planting activities and different plants.  Some planting mixes contain a slow release fertilizer and some contain special water holding granules.  A general purpose planting mix could be used for seed starting but it is much better to choose a special mix termed seed starting mix.    These mixes are finer in texture and some have been sterilized.  The label should plainly state – “seed starting mix”.  If you have tiny seed, hard to germinate, rare, or seeds with sentimental value always use a seed starting mix.

If you have larger, relatively inexpensive seeds you could choose a general purpose planting mix.  If you are a strict organic gardener you may want to check the label for things like inorganic fertilizers or moisture granules. There are organic mixes available and some even have organic fertilizers added.

Choose a brand name or a house brand made by a well-known company. ( Check house brand labels to see who makes them.)   Miracle Gro, Shultz, and Hyponex, and are some big name brands.  These companies are more likely to have quality control on their products and they stand behind them should some unlikely contamination or other problem occur.  Start with a small bag of the mix if possible, to see if you like it.  Different gardeners often prefer different brands of planting/seed starting mix.

Some gardeners prefer not to use mixes that have fertilizers and add their own fertilizer as the seedlings grow.  Just remember that if you do choose a mix that doesn’t have fertilizer that the normal minerals found in outside soil that plants need for growth won’t be there.  Seedlings can start growing quite well without added fertilizer but as they get their second and third set of leaves they really need some fertilizer added to the mix, if it doesn’t contain fertilizer.  If the mix does have fertilizer don’t add more.   The mixes use a slow release type of fertilizer that is good for at least 3 months.

Using the seed starting mix

Keep your seed starting mix closed until ready to use, in a warm location.  If the mix is cold let it warm to 60-70 degrees before you use it.  Make sure your planting containers are new or scrupulously cleaned before use.  For very expensive or rare seeds you may want to start with sterilized containers.  Always wet the seed planting mix before you put it in the containers.  Use warm water if you can as it absorbs better.  You’ll probably want a large bucket or bowl for mixing the soil and water. 

If you fill the containers with dry mix and try to add water the seed starting mix will float, areas of the mix may remain dry, and it’s just a general mess.  If you can, use warm rain water or distilled water rather than softened and treated water, which can contain minerals, salts, or chemicals that harm plants. When properly mixed your seed starting mix should be very moist, without dry pockets but water should not drip when you pick up a handful.  If you get the soil too moist put in containers with drainage holes and let it drain before planting the seeds.  Pack the soil into the containers with your fingers or with a small block of wood.

Check your seed packages or a good reference for the depth to plant seeds and how to space them.  Some growers prefer to cover fine seed with a sprinkle of clean sand instead of planting mix.  Make sure to label seeds, so you know what you started.  

If for some reason you must use soil or compost from outside or that has been previously used you should sterilize it.  Get it moist and spread it an inch or less thick on cookie sheets.  Bake at 160-200 degrees F. for 30 minutes.  The smell will not be appetizing.  Let it cool before using.

After you have transplanted seedlings into the garden you can re-use any planting mixture left in outside containers of annuals or put it on your compost pile.  It can also be worked into garden soil.