Compost and compost tea

By Kim Willis These articles are copyrighted and may not be copied or used without the permission of the author.

What is Compost?

Many home gardeners seem to agonize over composting, making it much harder than it really needs to be.  Composting at home is quite easy and anyone can do it successfully.  Compost is like black gold for your plants and it helps the environment too. Like anything else there are various methods of home composting and I’ll discuss a few of them here.

Compost is simply organic material, anything that was once living, that has been broken down by microbes and soil creatures such as earthworms 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.  It’s then called humus.

Why do home composting?

When you do composting at home you save all the wonderful nutrient value and soil amendment qualities of your waste and return it to your garden while saving space at the landfill.  You save money at home because you won’t need as much fertilizer.  Experts at Michigan State University say that if you leave the grass clippings when you mow and allow them to decompose, you can skip one application of fertilizer.  This is a natural form of composting.

If you have poor soil, either sandy, heavy clay or nutrient poor, then composting at home can take many of the things you might throw out and turn your garden soil into something rich and desirable.  There is nothing better for soil than organic matter and compost is organic matter that has been partially broken down.

If you do composting at home, you won’t be spending all that time bagging yard waste and taking it to the curb.   Some communities have passed a law prohibiting mixing yard waste with other trash.  You might have to haul it away yourself or pay for a separate collection if you don’t compost it at home.

Methods of Composting

Nature practices sheet composting.  A layer of leaves falls on the ground beneath the trees and lays there to rot.  You can do this too.  Don’t rake your leaves, run over them several times with the mower when they are on the lawn and let them stay where they are.  Let them blow into flower beds and stay there.  You can also spread your organic waste over the garden and just let it rot.

For many of us though, a layer of rotting garbage under the roses just doesn’t look right.  That’s why we make compost piles.  If you live in the country without close neighbors just make a pile for your organic waste.  It will eventually rot down to compost.  This is called cold composting.

If you live close to neighbors and don’t have much room, you want a small compost pile that rots quickly and without much smell. This is called hot composting, because the decaying process will heat up the pile.  When composting at home you can buy or build a number of items that will speed up the decaying process and hide what you are doing

Compost barrels or compost tumblers take small amounts of organic matter and rot them in a matter of weeks.  Turning the compost makes it rot faster and these compost barrels or compost tumblers make that easy. You’ll find them for sale in garden catalogs and stores. 

You can also make or buy compost bins.  These are just devices to hold small piles of organic matter which you will turn over with a shovel or pitchfork from time to time. You can make them from old pallets, a circle of wire, slats of wood or you can buy various bins on the market for home composting.

The disadvantage of compost tumblers, barrels and bins for composting at home is that they make only small quantities of compost at a time and you may need several to handle your waste.

Hot composting

In hot composting you want the pile to heat up quickly to around 150 degrees F. and remain that way for a couple weeks.  Hot composting makes finished compost faster and the heat caused by the decomp process kills some weed seeds and disease organisms.

You have a better chance of achieving hot composting if you do these things: make smaller piles- no more than a few yards of compost material, chop materials into small pieces, use at least 1-part green or moist material to 2 parts dry or brown matter, don’t layer but mix ingredients thoroughly and turn the pile once a week.

In some instances, you can have finished compost in 3-4 weeks with hot composting.  Very small piles may finish even sooner.  But it’s sometimes hard to get a pile to heat up and stay heated for proper hot composting.  Don’t worry, this compost may take longer but will be just as good.

Adding compost starters

It’s not necessary to add anything to get compost started, despite all the hoopla and sales pitches out there.  You don’t need microbes or anything but the proper ratio of greens and browns.  Nothing you buy will give you better or faster compost so don’t waste your money.  Don’t add other home products like Epsom salt, sour milk, lime, and so on either.  Some of these may impede the decomposition process.

If you really feel you must add something to get your compost started simply dig up a shovel full of garden soil and add that.  It isn’t necessary, but it makes some people avoid the magic potions being sold to make compost.

What to Compost

If you want to make compost quickly and without much smell, you want to put in equal amounts of juicy (green) matter and dry (brown) matter.  Compost needs to be moist to begin the decomposition process but if it is too wet, it will smell.  If you are managing a compost pile you may want to store some dry matter for times when you have a lot of juicy garbage.

Things that can used for composting at home include lawn and garden waste, which includes grass clippings, weeds, leaves, pruned material, dead plants and other things.  It can also include household waste such as vegetable peels, coffee grounds, egg shells, rotted fruits and vegetables and some food scraps.  You want to avoid putting meat, grease and a lot of sweet food waste into the compost pile.  These attract animals and smell. 

You can also use shredded paper, any paper except glossy colored pages.  That’s a good way to deal with junk mail!  If you have manure and used bedding from farm animals, or straw and hay, pile it on.   Don’t use manure from dogs and cats.  This may carry parasite eggs and diseases that are transmittable to humans. 

Anything that was once living (and manure, which was technically once living) can be composted, but don’t drag road kill home for the compost pile.  Farmers may compost dead animals, but they have been trained how to manage this and they don’t do it in the back yard.

The smaller the pieces that go into the pile the faster it will decompose.    Also turning the pile over every week or so will speed up the process.  If you have very dry weather and the compost dries out it won’t decompose either.  Adding moist (green) matter or water can help.

If you notice a smell from your pile it is probably too wet, or you have added meat scraps. You can add more dry material and/or protect the pile from heavy rain with a tarp to dampen the smell. 

Compost tea

If you want to start an argument among horticulture professionals just mention compost tea.  There are those that are positive it’s all bunk, those that think it’s good for everything and those who feel it’s something between the two extremes.  Until recently I was one of the people that felt compost tea was useless.  Then I came upon some research that made me reconsider my stance.  I just spent several days reading more recent published research on the topic and I have modified my position to some extent.

There is a lot of research on compost tea and when I talk about research I am speaking about science-based research that has been published in recognized professional journals and not popular garden magazines and websites. This research can be hard to wade through and one must be careful to not project what you want to hear/read about the topic onto the actual results.  You must also sort out laboratory and controlled environment results from those obtained under average garden or field conditions.  I’ll give you my opinion here based on my reading and I will also post some links at the bottom of the article, so you can do your own reading and analyzing. 

First let’s define compost tea.  The oldest version of compost tea is just putting some finished compost in a permeable bag of some sort- such as burlap- and letting it sit in a barrel of water for a few days. The brown water that results is compost tea. This passive method is often referred to as NCT. Some studies also refer to it as compost extract.

But aerated compost or brewed compost is also being used and complicated systems and equipment have been developed to make it.  The systems involve bubbling air through the compost-water mix.  A number of additives are also being pushed to make compost tea “better”.  These include molasses, sugars of other types, yeasts, and other concoctions.  Aerated compost tea is often referred to as ACT.

There are two major areas in which compost tea is thought to be helpful, that of a fertilizer and growth aid and as a suppressor of foliar, fruit and soil disease organisms.  The benefit is from the microorganisms, primarily bacteria, that compost tea contains as well as nutrients that leach from the compost into the water.

So, does compost tea work?   The answer seems to be- it might to some extent. If you are someone who doesn’t want to use- or can’t use - commercial fertilizers or pesticides to solve plant problems compost tea may be of some benefit to you. In research studies that compared compost tea application to conventional fertilizer or pesticides the conventional products were almost always more effective.  And in many cases compost tea often did not provide enough of a benefit to make using it viable in commercial production.  However, compost tea might be helpful as a last resort for home gardeners who have the time and like to experiment.

Before you get excited and rush out to brew compost tea read on.  Compost tea is so highly variable that the same results can’t be predicted from batch to batch.  What went into the compost, the conditions the tea was made under, the water pH and many other things all contribute to whether the compost tea will help, be neutral or even be harmful.  And fancy equipment or any additive don’t seem to make much difference in improving the usefulness of the product.

What went into the compost determines the tea results.  Better nutrient quality and disease suppression seems to come from certain types of compost than others.  Vermicompost (compost made by worms), compost made with manure and compost made with some kelp seem to be marginally more effective than other types of compost, including those made with so called super weeds and herbs.  More research needs to be done on this.

What you absolutely should not do is add supplements to your compost teas like molasses, sugars, yeast and so on, despite popular garden magazines and sites advice.  These things are said to feed the bacteria and increase the bacterial component of the tea. All compost will contain some harmful organisms like salmonella and E.coli, but in normal finished compost the numbers are low.  However, the addition of, molasses, sugars and other things may increase the population of these harmful bacteria to levels where they can pose a health hazard.  Organic grower standards prohibit the addition of these things to compost tea used on food crops and you shouldn’t use compost tea made with supplements on food crops either.

The problem with compost tea is that one doesn’t know what the bacterial content of the finished product is. (And no, you can’t look at a batch under a microscope and determine what’s there, without a lot of training or some very expensive and complicated lab equipment.)  Some compost tea seems to inhibit the production of flowers for example, and that may because of the bacteria prominent in that batch of tea. One batch may kill harmful fungal infections on plants and other batches made the same way may do nothing to control the problem. It’s a crap shoot on what you’ll get.

The fertilization efficiency of compost tea is also highly variable.  At most it is a very weak fertilizer.  One use of compost tea that seems to make some sense to me is using it to water seedlings in a soil-less planting mix.  You’ll add some nutrients, some soil bacteria and if you have the right bacteria in your tea it may help suppress the fungal disease called dampening off.

Using compost tea as a fertilizer for plants planted outside in the ground is useless.  Using the compost itself is far more effective.  Whole compost will provide more nutrients and will contribute more good soil bacteria to the soil than compost tea.  Either work the compost into the soil or apply it as mulch around your plants.

Compost tea needs to be made and applied frequently to be effective.  It doesn’t store or ship well so forget buying compost tea products in stores- they are pretty much worthless despite marketing claims.  Home gardeners should not sink money into fancy compost tea brewers either.  Research has found that some products that help the tea stick to foliage might improve the ability of compost tea to suppress plant diseases.

Compost tea may be helpful when you don’t have other options and for some specialized uses.  If researchers ever isolate what bacteria in soil and compost provide the most benefit and learn how to ensure that those bacteria and not useless or harmful bacteria can be increased and used, then we may have a good, reliable, natural control product from compost tea.  That hasn’t happened yet, but it’s a possibility in the future.