In the previous issue of this newsletter, we discussed the proper planting depth for trees and shrubs. Based on feedback from two well-respected arborists, I would like to clarify a statement in that article. Al-though I would prefer to get things right the first time, it was gratifying to know that people are reading this newsletter.|
The major cause of tree death in maintained landscapes may well be too deep or improper planting. I know many arborists who maintain this opinion. One extra bit of information that needs to be mentioned is that the reason trees die from deep planting is that moist soil or mulch around the base of the tree just above the root/trunk junction (the collar) does not allow gas exchange and the phloem cells die. Root physiology allows roots to survive underground, but trunk tissue needs oxygen and carbon dioxide exchange to occur more freely than in roots. The death of phloem cells sets up a series of events leading to dieback, decline, and ultimately death of the tree. We’ll talk about mulching woes in a future issue. For now, I want to concentrate on determining the proper depth to plant the tree.
I made a statement that all woody plant material should be planted at the same level as it was growing in the nursery. The assumption was that nursery stock is all at the proper level. I am now a believer that that is not always the case. Now, all of you nursery growers do not need to get up in arms against me either. Most of you are doing a fine, conscientious job, but just in case, read on.
In many nurseries, the cultivation practices around trees actually throw soil up around the trunk of the plant. This approach may be fairly well intended because often the nurseries are trying to avoid using herbicides. The problem is that when the crew comes through to prepare the plant for shipping, the soil is not removed. The tree is sold with the assumption that the ball is the correct planting depth. So how do we know what planting level is correct?
The root collar of the tree is the area just above the junction of the roots with the trunk. The collar is a few inches of the trunk all the way around the tree. The trunk should show a slight flare (widening) at the collar. The collar must not be buried with soil or mulch. When you plant a new tree or shrub, locate the main root/trunk junction first. The first root should be buried just below the soil line. When you get your tree or shrub for planting, loosen the burlap or root ball covering and carefully probe near the trunk to find the first large root. You may find that you need to remove some soil (sometimes several inches) from the top of the root ball before figuring the depth of the hole and placing the plant. Do this carefully so as not to injure the trunk or the roots. Hopefully, this simple process will provide you