ITG tree planting fall

It’s critical that trees are planted at the proper depth, with the root flare at the soil surface. This tree's root flare was identified by finding the first two roots coming out of the trunk.

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Most folks think of spring as the ideal planting time for trees and shrubs. However, fall offers a nice planting window with some added benefits over the spring season, making it my favorite time of year to establish woody plants.

Fall weather can create ideal planting conditions, with temperatures cooling off and roots requiring less moisture. In addition, we typically get a good amount of fall rains 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 time of high temperature and relatively low soil moisture. It’s a time where stresses on trees from drought, pest pressure or plant disease are serious, making the spring season less ideal for planting.

Some of the reasons 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- to 5-gallon pots, as opposed to larger, balled and burlaped (B&B) trees. These container plants are typically about 2 to 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.

Transplant shock is something that all trees and shrubs experience, which 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 adequate roots to overcome transplant shock.

We can really help a tree overcome transplant stress 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 to 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.

Trees that are planted too deep really struggle to get established and often suffer from a lifetime of other issues. It is the most common mistake in tree planting because we often plant our new trees at the depth of the container or root ball. However, the root flare of the tree is typically buried in the pot or the root ball on most nursery stock.

Before digging the planting hole, start by identifying the root flare on your new tree, if it isn’t easily identifiable. Gently dig down into the container or root ball to search for the first root or roots coming out of the trunk. If your plant was potted or balled too deeply, the trunk will have little taper, making the first roots your best indicator of the root flare.

I have been shocked at how deep the root flare is often buried in nursery stock. Earlier this week, I planted a tree with the McLean County Master Gardeners, and I would guess the root flare was 6 to 8 inches down in the pot. Therefore, my planting hole was only about 12 inches deep. I focused my digging effort on making the hole wider as opposed to deeper. After applying a nice layer of mulch and watering the tree in, I was satisfied that we set this tree up for successful growth.

Ryan Pankau is a horticulture educator with the University of Illinois Extension, serving Champaign, Ford, Iroquois and Vermilion counties.