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Transplanting – Should You Reduce Top Growth?

When transplanting trees, shrubs or perennials you tend to damage the root system. Common advice suggests that you should reduce the amount of top growth to match the root loss. This reduces the ratio of leaves to roots, and helps keep the plant in relative balance, making it easier for the plant to recover from transplant shock.

Is this sound advice? Does it apply to all kinds of plants?

tree roots

Abstract painting of tree roots by Robert Pavlis

Balancing Top Growth to Roots: The Theory

When a plant is moved, it is natural that you cut off some of it’s roots. With less roots, the plant no longer has enough roots to provide the required water for the amount of leaves above the ground. As discussed in the post Water When Plant Leaves Wilt, a lack of water results in wilting, and is not good for the plant. It only follows that it makes sense to reduce the number of leaves to “balance” the size of the new root system. This has been the standard advice and practice for many years.

Unfortunately this advice is not always correct.

Some Truths

There is certainly some truth in the above advice. Reducing the amount of leaves will reduce the water requirements on the roots. It is also true that with fewer roots, a plant has trouble absorbing as much water as before the move.

Removing Top Growth

What happens when you remove top growth?

The removal of top growth sends a signal to the plant that there is something wrong above ground. The plant goes into crisis mode and reacts by initiating the growth of dormant buds to replace the leaves it has just lost. This growth process requires energy; also known as a food source. The plant mobilizes stored food from the roots to the new growing points and puts a lot of it’s nutrient reserves into making new leaves.

This all sounds good, except that the plant also needs to grow new roots. This also requires stored food and nutrient reserves. The plant now has to share it’s reserves between the two processes. The net result is that both suffer.

From a plants point of view, roots are vital, and it is better for the plant to use all of it’s resources to make roots. This is especially true in late summer and fall since the plant has limited time to regrow a root structure to make it through the winter.

In some cases the plant is smarter than the gardener. Soon after trees are planted, they might loose some or all of their leaves without the gardener giving a helping hand. There are not enough nutrient reserves for both root and leaf growth, so the plant drops it’s leaves in favor of growing it’s root structure. I had a newly planted crab apple that went through most of the summer with no leaves. I was sure it was dead, but in spring it leafed out and now seems fine.

Perennials

In general, perennials seem to be less affected when they loose some of their roots and foliage during transplanting. If you are moving a large perennial and know that it lost a lot of roots, I think that the plant benefits from having some of the leaves removed. In practice, I only do this if I am moving something in mid summer when it has a lot of leaves and it is very hot.

I try not to move anything after June 15, unless it has been growing in a pot. If you are transplanting in fall, feel free to cut the top off–it is going to die off soon anyway.

Trees and Shrubs

Trees and shrubs need to be treated differently.

An important point to understand is that the woody part of these plants, ie the branches and twigs, are a place where the plant stores food reserves. In fact the old idea that in fall the plant sends all of it’s food to the roots is not true–but those details need to wait for another post. Food is stored throughout a woody plant.

Think of the woody parts as a snack for the plant. If you cut them off after transplanting, you take away food reserves the plant needs to grow roots. Clearly that is not a good thing.

Trees and shrubs respond just like other plants to having both roots and top growth reduced–they try to regrow both. Because their food resources are limited, the new root growth is limited, which makes it more difficult for the woody plant to make it through the winter.

The top growth of trees and shrubs should not be reduced after transplanting them.

You should remove any broken branches to help with the healing process. You should water well right up to the time that the ground is frozen. Leave all of the top growth. If there really are too many leaves for the remaining roots, the tree will take care of itself by shedding some leaves or having the leaves go dormant early.

Having said that, there are some extreme situations. If a woody plant has lost almost all of it’s roots, I might cut it back because without this it will die. The cuts should be made to take out large branches. You want to eliminate a lot of the dormant buds so they can’t grow and take energy from root growth.

Best Time to Prune Trees and Shrubs

Common advice is not to prune trees and shrubs in late summer and early fall. Turns out this information is not entirely correct. Have a look at Best Time to Prune Trees and Shrubs.

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Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

6 Responses to 'Transplanting – Should You Reduce Top Growth?'

  1. Alex says:

    Hello… i just transplanted a river birch (dura heat to be exact) about 7 feet, 3 clump. i had to move it from one location to another about 17 feet away so not a huge move. naturally the tree went into transplant shock. the top 1/3 of the leaves lost their color almost immediately and are now brown, curled up & crispy. they haven’t however fallen off. the lower 1/3 leaves are still green albeit slightly less in vigor.
    to complicate this transplant, within about 2 days of moving it, we got hit with a surprise storm. wind and rain, so much wind it was hurricane force gusts. the tree’s rootball starting pulling out of the ground. and was left leaning in the whole. i straightened it this morning and added a bit more soil.

    but now.. i’m really at a loss as to how this tree will respond. IF the top part of the tree dies… and doesn’t come back but the rest of the tree does. what do i do? i’ve read you should never top a tree. but it will drive me crazy seeing the top of the tree just dead twigs and the rest of the tree growing (my neighbor has a tree like that, and it looks so ugly). also should how long will it take for a tree to bounce back so to speak… will the top leaves re-grow??

    • A birch tree can be completely defoliated by caterpillars and it will just regrow leaves. Loss of leaves is more dramatic for us than the tree. The top branches contain sugars that the plant needs to grow roots, that is why we leave them. It will take a year or more to regrow all those lost roots, but it should be fine next spring.

      If the top does die back, you need to help it form new leaders – one for each main stem. Don’t cut the dead wood back just yet. Take a growing branch near the top, and force it to grow vertical by tying it to the dead leader. You will have to do this in stages – too much bending all at once will snap the branch. In 10 years you won’t know it ever had a problem.

  2. Margot Brinn says:

    Hello Robert, This is an unrelated question but don’t know where to post it. My soil seems to be inching up the PH scale; it’s now a little above 7. Is there anything other than sulphur [sp?] I can use, any mulch, compost etc that would lower it’s PH?

  3. Tamara E. says:

    I was always thinking of reducing transpirational water loss by pruning the top – it would be losing more water with the “excess” leaves in respect to the more limited roots which aren’t providing enough water. Lack of water, plant cell plasmolysis and death of leaves results.

    • That is the old advice, and it certainly seems to make a lot of sense. The problem is that top pruning also stimulates new bud development. The plant now has to grow roots and buds at the same time putting pressure on the important root growth.

      If transpiration is a problem the tree will shed leaves on its own while it grows roots. When it is ready it will grow the leaves back. The leaves are not needed for root growth, which uses energy and nutrients stored in the woody parts of the plant.

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