If you are interested in adding a new tree or shrub to your landscape, fall is a great time for planting. Our weather during the fall season often creates ideal conditions with temperatures cooling off and roots requiring less moisture. In addition, we typically get a good amount of fall rain to help ensure adequate soil moisture going into winter.
Although woody plants will experience dormancy in winter, root growth can still occur when soil temperatures are warm enough. This little bit of growth over winter, along with the fact that the soil has settled nicely, sets the tree up to hit the ground running when spring occurs.
When we plant in spring, soil moisture is typically high, and plentiful rainfall can be expected, but shortly thereafter, summer hits. Summer is a time of high temperatures and relatively low soil moisture. It’s a time when stresses on trees from drought, pest pressure or plant disease are serious, making the spring season less ideal for planting.
Some of the reason I favor fall for tree and shrub planting lies in my preference of plant material. Over the years, I have experienced the best luck with containerized plants in 3-5 gallon pots, as opposed to larger, balled and burlapped (B&B) trees. These container plants are typically about 2-4 feet tall and have a larger amount of root mass compared to above-ground growth. In contrast, B&B trees typically have less root mass to support the above-ground plant parts, often leading to greater opportunity for longer transplant stress.
After planting, all trees and shrubs experience transplant shock. This typically lasts for two to three years following transplant, or even longer.
To overcome transplant shock, trees and shrubs need to expand their root system beyond the planting hole. A mature tree will typically have a root system two to three times wider than the spread of its limbs. When you think about that ratio and how it would measure on a newly planted tree, it takes considerable time for a transplant to develop enough roots to support its continued canopy growth.
We can really help a tree overcome transplant shock by digging a shallow and very wide planting hole. The wide hole of well-loosened soil provides a nice medium for expanding root growth.
Your planting hole doesn’t need to be deep for a few reasons. First off, the majority of tree roots are concentrated in the upper 12-18 inches of soil. So there is no need to dig a hole much deeper. Secondly, and most importantly, it is critical that your tree is planted at the proper depth, which is typically much more shallow than expected.
To determine the proper planting depth, start by identifying the root flare, or trunk flare, on your new tree. This is the portion of the trunk at the bottom of a tree that begins to flare out, or taper out, as trunk tissue transitions into root tissue. Your tree needs to be planted so the trunk flare is at the soil surface.
If you’re not seeing a root flare, take the time to carefully dig down a bit into the pot or burlap to find it, and be sure that the hole you dig is not deeper than the root flare. For more information on proper tree planting, please see Illinois Extension’s Tree Planting Info Sheet at go.illinios.edu/treeplantingguide.
The East Central Illinois Master Naturalists are again hosting their Annual Native Tree and Shrub Sale this fall. Ordering is open now until Oct. 1. They offer a variety of native trees and shrubs for sale online with pick-up in Urbana on Oct. 17 and 18. This year’s sale also includes some native grasses and forbs. Don’t miss out! More information and ordering available at go.illinois.edu/nativesale.
Ryan Pankau is horticulture extension educator with University of Illinois Extension serving Champaign, Ford, Iroquois and Vermilion counties.
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