Tree Planting

Catalpa tree

 March and April are great months to plant trees for those in planting zones 6 and lower.  Bare root, balled and burlapped or potted trees all respond well to planting when the weather is cool and wet.  Early May is still fine for bare-root trees that have been well cared for and balled or potted trees and shrubs can be planted until late September if they are well cared for as they acclimate to a new spot.

Unfortunately, many old ideas about tree planting still exist among people who work in landscaping nurseries and garden stores.  Research done at places such as Michigan State University has helped us better understand the process a tree goes through when it has to re-establish itself after transplanting.  The newer advice, backed by research, helps ensure that your trees will get off to a better start and continue to grow for many, many years.  Here are some things that you should do or have your landscaper do, to get those new trees off to a healthy start.

This advice is for trees planted in the landscape, as ornamental or fruiting trees.  A re-forestation project, involving hundreds of small seedlings requires some adjustments to technique, although following the advice below would give those trees a great start too.

Don’t soak the tree roots for long

Do not put bare root trees in a pail of water for longer than an hour. You can moisten the packing material or wrap a bare root tree in some moistened paper, for holding for a day or two.  Keep them in a cool place.  Try not to hold bare root trees for more than a few days before planting.  Soaking the roots too long will rot them and the tree will probably die.

Make sure trees in pots or ball and burlapped are watered, but not too wet.  They must be able to drain well.  Do not sit pots or root balls directly in water.

Preparing the hole

 Prepare a hole three times as wide, but no deeper than the root ball.  If the tree is bare-root when you buy it, look at the trunk for a dark “ring” area to show you the level the tree was growing at before it was dug for the depth of your hole.  If it’s hard to determine the original growing level look for the highest branch root and make the hole just deep enough that the top root will be about an inch under the soil.

Contrary to what most people think, most types of trees have root systems that remain in the top three feet of soil.  Even if they are a species that has a deeper tap root, that root grows more slowly than lateral roots when first transplanted.  The tree needs to send out lateral, (side) roots so that it can start grabbing water and minerals to support new top growth and it needs to stabilize itself, so it doesn’t topple in the wind.   Having loose soil in a wide area around the root system is the key to faster establishment.

Planting at the right depth

Trees that are not planted at the right depth may grow, although some species are fussier about this than others.  But the tree may be in for a lifetime of problems if it wasn’t planted at the optimum level.  If you look at a mature tree that was planted at the right depth it will be wider at the bottom, the wider part is called a root flare.  Trees planted too deeply will have trunks that appear to be straight, without widening, right to the ground.  A trunk that flares at the bottom is stronger and able to withstand wind better.  Trees that were planted too shallow usually don’t survive to maturity.  

You get a tree planted at the right level by looking for that top root.  The highest root branching off the main root on the tree should be just below the ground, about 1 inch below it.  On some very small bare root trees you may need to look closely at the main root to see where branching is beginning.  

To see where the top branching root is in a balled and burlapped tree is you need to remove the burlap.  That will be covered in more detail below.   When trees are put into burlap roots may be twisted up higher than they were growing, and soil piled up above that.  You need to uncover the root system in that ball to see where the top root naturally lies.  With a potted tree you can usually line up the soil surface at the top of the pot with the ground level where you are planting it.  You will, of course, be removing the pot.

 Removing anything that isn’t “tree”

Once the tree is in the hole at the right level everything must be removed from around the root system.  Here is where many landscapers balk at the new recommendations that say all burlap, wire cages and even so called peat pots must be removed before filling in the hole.  You can leave the burlap on the root ball until it’s in the hole - where you can cut away most of it- but it should be removed.  There are a couple of good reasons to do this.   So called peat pots must be removed before the roots are placed in the hole.

Modern “burlap” is often composed of synthetic materials that really don’t break down quickly in soil.   Tree roots may still be contained in those packages years after planting.  That’s not a good thing because the roots need to spread out to support new top growth.  And any burlap that gets exposed to the air wicks moisture away from tree roots.  Peat pots are even worse at restricting root spreading.  Trees need to get those lateral roots growing the first few months after planting, not years down the line.

And you need to inspect that root system before you fill the hole, another reason to remove burlap.  Roots that have circled around and around in pots or burlap balls will continue to grow in circles after being placed into the ground.  This may eventually strangle the tree, even years after planting.  And as mentioned above, you need to know where the top branching root is to properly place the root system.

Make sure all strings, wire, rope etc. are also removed from the roots and also the trunk and branches of a tree.  As a tree grows these things cut through the area that transports food and water and any parts above the constricting item will die.

Root washing- should you do it?

Many garden professionals are now advocating that all the soil be washed off the roots of trees and shrubs that you purchase in pots or that are balled and burlapped.  When you remove the soil, you can see the root system and correct any problems or if the plant ‘s roots are in horrible shape, you can return it for a refund- sometimes.  Some experts think removing the soil around the roots helps plants adjust more quickly to the new soil they will be planted into.

To root wash all you do is remove pots or burlap and use a hose to gently wash away all the soil. If you can’t use a hose, you can sometimes use buckets of water or set the plants roots in a tub off water and swish it gently.  It can take a little work to get all the soil out if the plant is badly pot bound.

After the soil is washed away you can untangle the roots, clip off badly circling roots, and spread the roots out. (See the section below about helping roots grow right.)  Keep the roots damp as you work on them. Washing the roots doesn’t usually damage them much, so don’t worry about that.  And roots can withstand a bit of pruning without harm too. 

If you root wash, you must be prepared to plant the tree or shrub immediately after the soil is washed away and problems corrected.  You can’t leave it sitting in the open air where the roots will dry out.  If you are planting several trees at once you could wrap the washed roots in wet cloth or paper for an hour or so.  Keep them out of the wind and sun until planted.

I am not totally swayed by the root washing theory, at least for all plants.  If I remove the pot or burlap and there are few roots on the outside of the root ball, I remove a bit of potting soil at the top until I uncover the top horizontal root to find the correct planting depth and leave it at that. Sometimes a gentle shake or thump will dislodge enough soil so the roots can be seen. If soil crumbles away from the roots and I can spread them easily horizontally I will plant those trees without washing the roots.

If you remove a tree or shrub from a pot or burlap and you see that the rootball is very root bound and there appears to be circling roots, then it’s a good idea to wash off the soil and examine the root structure.  For very expensive trees or shrubs a careful root washing might be a good precaution.

If you wash the roots and the plant has badly circling roots, the worse case scenario, you may want to take it back to where you purchased it for a refund/replacement.  The plant will probably not survive if planted like this. However, some places may not accept a plant back that’s been root washed and is out of the container.  That’s wrong, but it’s a hard thing to challenge. 

Helping roots grow right

When planting trees never wrap a root around the hole- spread it out horizontally.  If it’s really too long, trim it off to fit the hole, but never spiral it around the hole.  When you see those roots that have circled the pot as described above, they must be loosened before replacing soil.   If you can loosen them with your fingers and spread them out that’s a sign the circling wasn’t too advanced.   Good nurseries either root trim or repot trees to keep them from getting root bound.

If the roots are thickly layered at the bottom of the pot or root ball or around the sides you’ll need to trim them.  If it’s just at the bottom, trim off the circling roots, making a slice across the bottom an inch or so deep.  Then slightly flare out the remaining soil and roots.  If roots are really circled heavily up the side of the pot make several cuts length wise through the roots, as well as trimming the bottom, and hope for the best.

Roots that are circling when planted will probably continue to spiral around the main root or trunk.  This may eventually kill the tree by choking off the supply of water and food, sometimes years after planting. 

Spread roots sideways in the planting hole, except for any central main root.   Don’t squish all the roots down vertically into the hole.   Any larger roots that are broken can be trimmed.

Refill with what you removed

You’ll see the signs advising you to buy amendments and the sales staff may try to convince you, but don’t buy peat or topsoil or anything else to add to the planting soil as you plant your tree.  Research has shown that trees establish better if the hole is refilled with what you took out.  After all, that is the soil that the tree will be living in after the roots grow through your small amended area.  It is easier for the tree to adapt to new conditions if it starts right away and it doesn’t have to re-adjust its root system when it grows through the amendments and into the surrounding soil.

Holes filled with “good stuff” may hold too much moisture next to roots, especially if you throw a bag of peat into heavy clay soil.  The roots sit in water and rot.  And trees may not extend their roots quickly into surrounding soil if it’s easier to grow roots inside an amended area.  This can lead to circling roots, with the tree being strangled or to a poorly established root system that can’t support the tree in a wind storm or through a drought.

You can add a little slow release fertilizer to the soil you are going to backfill with.  Don’t throw it in the hole, mix it into the soil you removed and then refill the hole.

This tree is being planted too deeply

Don’t prune and don’t stake- usually

It’s not necessary to remove one third of the tree as some older advice may lead you to believe.  Research has shown the tree needs top growth to make food so the root system can grow. Prune off any broken branches and any branches that cross or rub each other, that’s all.  You can shape the tree once it has established itself, usually after one growing season.

Most new trees should not be staked.  They grow stronger trunks and wider root systems if the tree is allowed to sway in the wind.  There are some exceptions.  New evergreens planted in the fall or in high wind areas may need to be staked for one growing season.  Some ornamental weeping trees will need to be staked at least for a growing season, some for much longer.  If you do stake a tree check the ropes several times a year to make sure they are not cutting into the tree.

Don’t over water and don’t over mulch

Yes, newly planted trees need to be well watered at planting and they should be watered when needed during the first growing season to get them off to a good start.  But their roots don’t need to be constantly soaked.   In really hot weather and in sandy soil trees may need watering frequently but, in most situations, a good watering once a week the first season will be enough.

Mulch is good for trees, but it shouldn’t actually touch the tree trunk.  Rot and disease can start where decomposing mulch touches trees.  And never use more than 3 inches of mulch.  Too much mulch absorbs or sheds water before it gets to the soil and it prevents oxygen from reaching tree roots.  To get water and air tree roots may grow up into the mulch instead of down into the soil, which isn’t good for the tree. 

A little care taken during tree planting will do a lot to prevent tree failure.  A tree may leaf out and appear to grow the first season or even several seasons but failure of a tree in the first three years after planting is often due to poor planting procedures. When contracting with a nursery or landscaper to plant your trees make sure they are willing to follow your directions and plant properly.  You are the customer.  If they say your warranty is void if you remove burlap for example, you may want to use another company.  They may replace the tree, but you will have lost valuable growing time if it needs to be replaced.  And unfortunately, the tree may not start to decline until the warranty is up.

You plant trees for the future.  Plant one soon.