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Saturday, October 1, 2022
Letter: Research offers different take on planting trees and shrubs

Dear editor:

I have nothing but respect and admiration for Lake Report gardening columnist Joanne Young and the work she does in and for our community.

However, based on peer-reviewed research, I would like to offer a much different approach on how to plant trees and shrubs as we move into planting season.

In order to develop a strong and healthy tree that is not dependent on you for regular watering and feeding, you want to encourage a newly planted tree to flourish in your native soil – the soil in your garden right now.

If you have compacted soil, you might need to loosen it so the roots can penetrate downward.

If you follow the science, best practices involve choosing trees and shrubs well-suited to the site, remove the growing medium as much as possible, correct any root circling to prevent girdling and plant in your unamended native soil. Mulch and water.

Any potting mix should be removed if you are able and placed on the top of the root zone after backfilling with the soil that came out of the hole.

Amending the soil prior to planting trees and shrubs is not supported by any published peer-reviewed research I can find. I

In fact, this can create a textural barrier between soil types, which will slow water movement and can lead to a perched water table. If you amend soil around the root ball you increase the risk of girdling long term.

When the roots reach the edge of the improved soil they curl back. Roots can be lazy. Why plow into native soil if you can just keep circling in the easy-to-traverse amended soil?

Adding phosphorus, potassium or other minerals to your soil should only be done if a soil test (the University of Guelph provides an excellent service) or a home test kit (not always as reliable) shows your soil is deficient in one of these minerals.

When Joanne says, “If you feed your soil, your soil will feed your plants,” she is correct. The best way to feed your soil is to top your garden with an inch or so of compost annually and top dress with a couple of inches of mulch.

Mulch around your tree a few feet out from the trunk (at least to the drip line) and never let mulch touch the trunk of the tree or any garden plant.

Repeated studies have shown that arborist mulch is the most beneficial for your soil. Any organic compost should be added to the top of your soil, not mixed into it.

If in doubt, mimic Mother Nature. Stay away from commercial fertilizers if you can.

When placing your tree in the hole, be sure to keep the root flare above the soil line. Do not assume that planting your new purchase at the same depth as it was in the container is correct.

The root flare must be above the soil for your tree or shrub to flourish. Be vigilant for roots that are growing in a circular pattern.

These become girdling roots and will eventually strangle your tree.

I have included a photo of two eastern redbuds removed on Victoria Street last week. You can see how the roots encircled the trunk and killed the tree.

Only stake your tree if it needs support, needs anchorage (if subjected to constant strong north winds) or needs protection from injury.

For a step by step, easy to read, science based, peer reviewed explanation on tree planting, check out these links: or

For an excellent step-by-step guide, Google “Purdue Extension Tree Installation: Process and Practices (FNR-433-W)”

There are many conflicting and confusing gardening practices out there. If you Google “ext” at the end of your search, you will get better hits. Extension sites from horticultural departments at universities are your best sources.

Brian Capon's “Botany for Gardeners” (third edition) and Robert Pavlis' Soil “Science for Gardeners” are good reads.

Happy gardening.

Betty Knight

Master gardener