Transplanting trees? Here’s why you should stick to the smaller ones.

One of the things I have learned over years of hiking countless mountain miles is the ‘trail principle’.

When hoping to get from point A to point B, I’ve tried (and failed) applying the mathematical truth that the shortest distance is a straight line. While true in math, it doesn’t apply to mountain travel. I’ve learned instead that if a trail is present, take it. That trail may be made by humans, wildlife, or even cattle. Its simple existence reveals the path many prior travelers have found tried and true. Shortcuts have seldom proven quicker or easier for me.

I read an article recently that reiterated this principle in planting trees. When planting a tree, we invariably want it to be bigger faster. Unfortunately, larger trees undergo a prolonged period of transplant shock or slow growth after being transplanted. The length of this period of stagnancy is directly correlated to the size of the tree at planting time.

Smaller trees planted at the same time as a larger tree will have a much shorter recovery following transplanting. It may even surpass the larger tree in size before the larger tree has fully recovered its normal growth rate.

This quandary is explained by the root-to-shoot balance. In other words, a tree must balance its above and below ground portions to achieve healthy, regular growth. In an article by Faith Appelquist in the Tree Quality newsletter, she stated that as much as 98% of a tree’s root system is left behind when it is dug for transplanting. Often less than 5% of the absorbing roots are moved with the tree. Other references aren’t as extreme, but the principle is sound. This is true of both small and large trees.

However, because the roots of both grow at the same rate (1-2 feet/year), A smaller tree can quickly re-establish an adequate root system to support the above ground tree. A larger tree experiences a long period of slow top growth as it is trying to replace its significantly compromised root system.

To illustrate the point in her article, Faith gave the example of planting a 4-inch versus a 10-inch diameter tree. The smaller tree will have reestablished its root system in 5 years, whereas the 10-inch tree will take 13 years to replace its lost roots. The result is that the smaller tree will have several years of vigorous top growth while the larger is still struggling to replace its roots. In the meantime, the 4-inch tree is healthier and has outgrown the 10-inch tree. I also found this comparison in other references.

A general guide is that for every inch in diameter beyond a 1-inch diameter (referred to as a 1-inch caliper tree) will add one year of recovery time to the tree. The translation is that in 5 years, a 1-inch caliper tree will be the same size (or larger) as the 4-inch caliper tree planted at the same time.

Since larger trees are much more expensive, my advice is to choose the smaller tree and practice patience. There are ways to shorten transplant shock with larger trees, but these are more costly and there is still elevated stress on transplanting larger trees that may lead to insect and disease issues. Just as I’ve learned the value of sticking to a trail while hiking, shortcuts to larger trees seldom result in the desired outcome.