Everyday Gardener // For healthy trees, dont plant too deeply

This spring, a red oak tree someone planted decades ago on the southern most edge of our yard is coming down. Hollow to the point of being hazardous, city arborists sprayed it with an orange X last fall. Once the snow melts, I imagine it won’t be long before they’re back armed with chainsaws and a bucket truck.

The city is removing the tree because it’s so close to the sidewalk, it falls under their jurisdiction rather than ours as property owners. As happy as we are not to be out the thousands of dollars it was going to cost to have it cut down, it’s sad that the very location that spared our wallets is probably largely to blame for that beautiful tree’s early demise.

Just inches from the sidewalk, the tree has suffered repeated injuries when concrete repairs and street work left its root system badly damaged. Add to that the fact that the tree, which leans way out over the street, must have begun its life in the shade of a much larger tree, forcing it to reach and strain to get some life-sustaining sun, and you’ve got yourself the equivalent of a kid raised by parents who fed him when they felt like it while binding his feet constantly. Poor tree.

Sadly, the premature death of trees, particularly in urban areas where they have to endure things like road salt and hot, dry boulevard strips, is not uncommon. A poor location, lack of water and nutrients, pests, damage from one thing or another, all of these things can injure or kill a tree. You may not know, though, that one of the easiest ways to condemn a tree to a slow but sure death is to plant it too deeply. And, as it turns out, all of us, even the experts have been doing that for a very long time.

Until very recently, it was not uncommon to hear experts say it was a good idea to plant trees deeply to protect them from things like wind damage. Now, thanks to researchers who study trees, including Gary Johnson at the University of Minnesota, we know that this advice was wrong.

Results from a nine-year study by the university, for example, made clear that when a tree is planted too deeply it develops stem-girdling roots that literally choke it to death over time by encircling the trunk as it grows. It sounds like the stuff of horror movies, but these roots are really just trying to help the tree get what it needs to survive.

When a tree is planted at the correct depth, its roots are very close to the soil surface where there is plenty of air, water and nutrients. If roots are too far below ground to do their job, they begin to reach upward. Circling and winding as they go, they constrict the tree’s trunk like a noose around a neck.

You can tell if a tree is planted too deeply if you look at the spot where the trunk goes into the ground and what you see looks a lot like a telephone pole. You may even see some of those girdling roots coming up out of the ground and wrapping around or crossing over the trunk at soil level. (When you start looking, you’ll be amazed at how many telephone-pole trunks you see.) It may take 10 years, maybe more, but trees planted this way will eventually decline and die.

Thankfully, now that we understand what we need to do, it’s easy to plant trees at the right depth. Before you start digging your hole, you need to find the tree’s root flare (or root collar). The root flare is where the main stem transitions to the roots at the base of the trunk, and it looks like a bump or bulge, really. If your tree is in a container of manageable size, gently slide it out onto the ground and using your hands, and probably a trowel, scrape away the top layer of soil until you expose the flare.

Dig your hole and place the tree at the bottom of it so that when you’re finished filling the hole with soil, the flare will be above the ground not below it. As always, once your tree is planted, be sure to water it in well. For the first few weeks, watch to be sure the soil doesn’t settle too much and cause the flare to sink into the ground. If this happens, pat the soil down gently but firmly and reposition the tree as it should be.

Meleah Maynard is a Master Gardener and freelance writer. If you have questions for her contact her at [email protected]