Shrub and Tree Transplanting: Plant Them Too Deep and Lose Them

Excessive planting depths kill untold numbers of newly installed trees and shrubs each year. I seem to harp on this subject because many gardeners continue to experience dying or stunted plants as a result of this practice. The symptoms of excessively deep planting mimic other causes, so it is easy dismiss, blaming planting failures on some other factor, and repeat the mistake again the next time that transplanting is done.

An interesting study that addresses this issue is underway at the University of Florida in Gainesville. Various species of trees and shrubs have been installed at different planting depths. The goal is determining the effects that depth of installation has on establishment and subsequent growth of these plants.

Planting depths included in this research are: 1) the top of the root ball slightly above grade; 2) the top of the root ball even with the top of the ground; 3) two inches below the soil surface and 4) four inches below the surface. Obviously, being a University experiment, this is a randomized and replicated design that involves large numbers of plants.

I had an opportunity to go to the field and see this work about a month ago, and differences so far, are obvious. The trees and shrubs that were planted 2 and 4 inches below grade are easy to find. They are stunted and in some cases, in decline. The study has not been completed, but when it has run its course the information will be published.

Shrubs and trees that are planted too deeply can be damaged in two different ways. With few exceptions, the roots of these plants must receive atmospheric oxygen in order to survive. If plunged too deep in the soil, root suffocation begins almost immediately.

Deep planting also can girdle the base of plants. Stems and trunks, being above ground plant parts, differ from root tissue. If soil is placed against these parts that are accustomed to air, then rot organisms begin to break down the bark and work its way into the vascular system. Once the tubes that move water, minerals and food within the plant are interrupted, then the plant eventually dies.

So, What’s the Right Planting Depth?

Dr. Ed Gilman, the researcher who is conducting the study, recommends planting relatively shallow. In fact, he provided a good rule of thumb for use when transplanting. “Leave the uppermost root showing” when the job is complete.

That might seem extreme, but take a look at the top of the potting medium the next time that you purchase a tree or shrub. Almost without exception, you can see one or more larger roots partially exposed at the surface. This is the depth at which that particular plant grows. If we duplicate that depth when it goes into the ground, there is a much better chance of success.

Question of the Week: My lawn has a spongy feel when walked upon and someone told me that I should have it de-thatched. When is the best time to do this?

Answer: Wait until spring. Thatch removal is stressful, so by timing this procedure to coincide with the spring flush of growth, the lawn will be able to recover more quickly.