Time to Bust this Myth: “Do NOT Amend Soil when Planting Trees”

By Don Engebretson, the Renegade Gardener

Well gee, um, OK, I won’t, even though it goes against every shred of instinct I’ve developed over my years and years of gardening. But if you say so…

WHO says so? Why, just about every member of this year’s new crop of TV gardening experts, tired old garden writers and gullible radio gardening experts, that’s who. They have forwarded this myth along to the point it’s now considered the “in” fact to know about tree planting — except it’s wrong. Here’s the whole story:

Researchers at the University of Minnesota discovered that the best way to plant a tree was to plant it in as big a hole as possible. Instead of digging a hole twice the diameter of the pot or root ball, you should dig and rototill and break up the soil around the new tree as wide as possible. Otherwise, the roots of the tree start circling in the hole, where the soil is loose, instead of breaking through and heading out to establish a broad, long root structure.

The U also found that if the soil was amended in a too-small hole, this encouraged the tree’s roots to circle, and never leave the safe confines of amended soil. In these situations, the trees suffer and are prone to disease and drought problems because their roots never get very far from home.

They did not say to never amend the soil, and two months ago the top tree expert at the U’s School of Horticulture confirmed this to me in person.

If you dig a hole for a tree and the soil is junk, just crappy, inert, lifeless junk, the stuff you often find in a yard underneath the ribbon of black topsoil, it’s ridiculous to miss this opportunity to add some organic matter to the soil that you use to fill in the hole after planting. The tree needs organic microbes and fungi in the soil to survive. But don’t dig a small hole — dig as wide a hole as possible.