April is a great time to plant new shrubs and trees. Here are tips from the Hudson Valley Horticulture newsletter:
Don’t Get in too Deep: Planting Depth Tips for Trees and Shrubs
Within the first couple of years too many newly planted trees or shrubs struggle and eventually die. Many factors can cause this problem, but one that is often overlooked but very common is a planting depth that is too deep. I have seen it with plugs and seedlings in greenhouses, with liner stock in nurseries, and seedlings in Christmas tree farms, as well as larger trees and shrubs in landscape and street tree plantings.
There are many reasons deep planting can happen. Often I think the person doing the planting feels like they are going the extra mile by getting the plant down a little further. They know it can work for tomato transplants but arent aware it can be lethal to woody plants.
In the case of nurseries, it can occur gradually. Where cultivation is used to control weeds, soil is often thrown against the trunk in the process and builds up over time. Also, while digging trees to be balled and burlapped, extra soil often ends up with on top of the root ball, then at planting the hole is dug to the level of the burlap and not the root flare.
Reasons Deep Planting is a Problem:
Lack of oxygen and build up of carbon dioxide. The fine fibrous roots normally near the surface need to use oxygen to do their work of making water and nutrients available to the rest of the plant. The oxygen content of soils declines as the soil depth increases so if the plant goes in too deep the roots will not be able to breath. In fact on heavy textured or compacted soils the rate of gaseous movement (diffusion of O2 into the soil and CO2 out) drops off very rapidly so root growth is hindered and eventually ceases at these depths where the oxygen levels are too low.
Higher moisture deeper in the soil. Not only will water occupy pore spaces and displace oxygen rich air, it can also help the spread of disease organisms. Some fungi like Pythium and Phytophthora require higher levels of soil water for their spores to move. Others diseases are better able to attack plants weakened from water logged roots.
The difference between trunks and roots. Stem and bark tissue, unlike roots, is not designed to withstand soil contact. When soil is packed around stems or trunks, the protective tissue can become saturated and weakened so it loses its defensive properties. Deteriorated bark and stems inhibit the growth of the plant and can allow certain insects or diseases to feed on the vital pipework of the plant just inside the bark layer.
Future problem with girdling roots. If the trunk is below the soil level it is vulnerable to girdling roots. These start as roots that grow near, and often around, the trunk, then as both the tree and roots increase in girth the vascular tissue of the trunk can be constricted. Girdling roots can increase the chance of a storm blow-over, branch dieback and even the death of the tree.
To get the planting depth right, simply make sure that the root flare or the top most roots are planted at the surface. This may require removing some soil from the trunk to find the root flare. If a balled and burlapped tree or shrub is planted so the burlap is level with the soil surface it will often be in too deep. Careful attention to planting depth is an important first step to increase plant vigor and resistance to insects and diseases.
Written by: Brian Eshenaur, NYS IPM, email@example.com