A topic that comes up frequently in calls that I receive is the planting of trees and shrubs.  Usually the caller wants to know when the best time of the year to transplant is.  As is often the case, the call doesn’t come to me during the optimal time of the year for transplanting, so I have to evaluate the situation and describe the risks to the homeowner.

For deciduous trees and shrubs, the optimal time for transplanting is in the late dormant season, usually in March.  That doesn’t mean that you can’t transplant a tree or shrub at other times of the year, but the farther away you are from the dormant season, the higher the risk.  I wouldn’t advise transplanting a valuable tree or shrub in midsummer, for example. 

Of course, there are a lot of variables even when thinking about summer transplanting.  How large is the plant?  Larger trees and shrubs are more of a challenge to transplant.  Small seedlings will have a greater chance of success.

You also need to take into consideration the plant’s stage of growth.  Dormant plants make for easy transplanting.  A plant that has fully developed leaves on it will be more of a challenge.  In fact, your chances of success are much slimmer with a plant that is actively growing.

The first year or two are the most critical for the new transplant.  What you need to be thinking about... and constantly monitoring... is water. 

The reason that water is so critical during this phase of the plant’s life is that its water gathering capacity is severely limited after transplanting.  When a plant is growing in a nursery, the roots extend out from the plant for a surprising distance.  It’s the end of those roots where root hairs develop.  These structures are where water and nutrients are taken into the root system.

When you dig up a transplant, most of the roots are left behind, including the roots with those all-important root hairs.  Even if you’re the one digging the plant up, it’s hard to get them all.

So for the first year or two, the plant has to redevelop its root system.  That means it’s going to need frequent water.  But not too much.  Too much water is just as bad as too little.

One problem that should be mentioned with heavy soils is the “clay pot” effect.  Sometimes homeowners, with the best of intentions, dig a large hole for their new plant and mix the most desirable materials they can think of into the soil that they put back in the hole around the plant.  They may add peat moss, leaf mold, or whatever they think the plant may like.

This is an acceptable practice in a sandy soil, but in a clay soil, this can spell disaster during a rainy growing season.  The reason is all that organic matter does a great job of holding water.  In a rainy season you will end up with a hole filled with high organic matter soil, and lots of water.  The problem is that the water will not drain off easily into the surrounding soil, because of the soil’s high clay content.  So you end up with a “clay pot” effect.  The result is that the plant is sitting in this superabundance of moisture, and it doesn’t like it. If you have a heavy clay soil, it’s best to just put the same soil that came out of the hole right back in, with no modification.

If you find yourself in a situation like this, with a poorly-drained soil, you may be able to help things with a raised bed.  This will promote drainage.  Raised beds work particularly well for shrubs and smaller trees.

If you would like more information on planting trees, University of Missouri has a guide sheet with lots of tips.  Call your local Extension center and ask for guide sheet G6850, “How to Plant a Tree.”