Q: I received some small bare root trees and wonder how to plant them properly. How deep should the hole be?
A: I cannot tell you exactly how deep to dig the hole for your bare root trees because it depends on the root mass of each individual tree. Generally you need a wide, shallow hole because a tree’s root system will spread wider rather than deeper.
A common misconception is that a tree’s root system mirrors its top growth. However, many years of research demonstrates that is not the case. A tree’s root system is comprised of the larger anchor roots that primarily function to stabilize the tree in the ground and hold it upright, as well as a large network of fine feeder roots that are responsible for absorbing water and nutrients from the soil.
These typically spread out one to two times the height of tree and are found in the top six to eighteen inches of soil. Roots need oxygen and adequate moisture, which are usually found in the same part of the soil profile. One the most common reasons that trees fail to establish and thrive is that they are planted too deeply, which deprives them of the necessary oxygen.
A good rule of thumb is to plant trees so that the root collar is right at ground level. The root collar, also known as the trunk flare, is the swelling of the trunk where it meets the roots. While this is easy to see in a mature tree, it is also visible in your small seedlings.
When planting bare root trees, dig the hole deep enough and wide enough so that you can build a cone of soil in the bottom of the planting hole. Spread the sapling’s roots evenly over the cone and into the hole so that they are not bent or curled in any way.
Jamming tree roots into a hole that is not wide enough often results in circling roots that can become girdling roots as the tree grows and matures. These are roots that grow against and into the trunk. As both root and trunk grow in diameter, the impingement can cut off the flow of water and nutrients to that side of the tree. In severe cases, a girdling root can completely encircle the trunk, and tree winds up choking itself to death. Girdling roots can also make a tree more susceptible to wind throw. Make sure the root collar sits atop the cone so that it winds up just at the soil surface.
You can create a shallow berm around the edge of the planting hole so that it catches and holds water. Water the saplings after planting to settle the soil and force out any air pockets. Do not place any fertilizer in the planting holes as it can burn the tender roots when they start to grow. Hold off until next spring, and fertilize based on soil test results.