Will Grinding Down Tree Roots Improve a Lawn?

Q. Sarah in Pennington, NJ writes: "I watch your weekly television show for advice, especially concerning grass, trees and shrubs. I live in a condominium and the landscaper hired by the condo association has been grinding down the roots of maple (and other) trees that show at the surface. The association's contracted landscaper believes that this will help turf grow better under these trees. Do you have any advice concerning this practice that I could pass along to them?

A. Boy do I have advice for them! I got a bucketful of advice! A Lincoln Town Car full of advice; advice that could take days in the blasting out of! But mine is (hopefully) a family show and I don't want to force any children watching or listening out there to have to explain what some of the words mean to their parents.

But most of the advice would start with the classic: "What the...?"

Above ground tree roots are the sign of a healthy tree. Those above-ground roots are proof that the tree isn't planted too deeply or smothered in cheap toxic wood mulch. Above-ground roots are also--in my opinion--one of the handsomest parts of a tree; sinew and muscle that remind us of how quietly powerful these silent giants are, especially in winter, when the only thing you got to look at on a deciduous tree is roots and bark. And, as Sarah seems to suspect, the torture of grinding those roots down will weaken the tree, perhaps unto death.

Which brings us to the subject of trees and lawns, which is generally a horticultural affectation as opposed to an imitation of nature. In the real world, turfgrass thrives in the absence of trees; free from the shade cast by the trees in the summer and the tree-mendous struggle to take up enough of the water and nutrients that the trees would rather take for their own.

And deciduous trees in nature have evolved to add a third level of competition--the annual dropping of their leaves in fall smothers most of the smaller plants on the forest floor, which is why the grassy weeds that bedevil gardeners just aren't seen in the deep woods.

Yes, you often do see a lawn and a tree make nice, with grass growing right up to the trunk. These are always "specimen trees" that stand alone, where the lawn can receive sun from all sides. Once you get a lot of trees, you get less lawn. The best way for trees and turf to play nicely together is to note the natural range of the grass around the tree. Let's say it starts thinning out about five feet away from the trunk. That's where you stop trying to grow grass and instead make a natural-looking divider of mulch: compost, arborist wood chips or pine straw--which is becoming more and more available in the mid-Atlantic states.

Whichever mulch you choose, spread it one to two inches deep beginning about six inches away from the trunk and out into a nice circle that ends where the grass begins to look good. Now the roots are covered. And for this kind of issue I strongly recommend you seek out pine straw as it will suppress the grass but allow those above-ground roots to breathe. It looks nice too--the visual effect will be pleasing, and the landscaper can't complain about difficulty mowing or weed whacking.

Now--what if there's a situation where a tree is displayed out in the open, grass seems to do well under it, and it has above ground roots? Now the mulch has to be compost--or, in this case, it could also be composted manure--as both the tree and the turf would love the nitrogen that composted manure provides. (Just make sure that the manure is COMPLETELY composted, as unfinished horse manure will give you more weeds than you had in your first garden.)

But instead of one to two inches, begin with half an inch. Allow the grass to grow up into the compost and/or manure, then add another half inch. Keep adding small amounts until the roots are completely covered--being careful not to allow any compost and/or manure to touch the trunk of the tree.

Yes, now we have 'the mowing problem'--how to keep the grass looking nice without big mowing machines constantly banging into the tree like bumper cars on drugs or whipping it apart with a weed whacker. The answer? SLOW DOWN!

I see landscapers and their helpers who think that their zero radius turn mowers are competitors in the Indy 500. If there were more than one mower working in a small area, I'm certain one of them would try and bump-pass the other mower into the wall. I know that time is money for landscaping crews, but the speed at which some of these people are operating is patently ridiculous.

If you want to sculpt the perfect union of grass and tree, you need to take your time. If you don't want to take your time, create the protective ring of mulch. But for the sake of common sense, do not grind down the roots of a tree--or Groot will come and get you!