Working with and around tree roots

Published 11:18 am Tuesday, April 5, 2022

By Felder Rushing

Question comes up nearly every week: Can I cover up the exposed roots of my tree? The mower keeps stalling out on them, the mailman trips on them, kids can’t play there, grass died and I’ve tried everything but it won’t grow back…”

The short answer is “Yes” – just don’t kill your tree in the process.

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In spite of popular myths, trees aren’t naturally deep- or shallow-rooted; depending on soil type and the availability of both water and air, trees we think of as shallow-rooted can have roots many feet deep, and allegedly deep-rooted trees often have roots right on the surface. You’ve seen them blown over, with roots only a foot or two deep.

This is because though roots generally grow downward, they require oxygen to process stuff; if the soil is heavy clay or poorly drained and stays wet for weeks on end, roots can’t get the oxygen they need and they either don’t grow deep or those that do rot.

Bottom line is, if a tree has roots on top of the ground, it’s usually because they can’t grow any deeper, so covering them up more than just a couple of inches or so with dirt can suffocate them. Not always but believe me I see I happen all the time.

So, what to do? There are three good options (four, really, if not noticing them at all counts). You can celebrate them by clearing away leaves and let them be prominent; you can cover them with a mulch of leaves, bark, pine straw, gravel, chipped slate, spaced-out flagstone, or other porous material that still lets air and water get to the roots; or you can plant shade loving groundcovers or small shrubs. All three work and are done commonly in botanic gardens.

I like the first one, in which a distinct line is cut into the ground outside the exposed roots so the area has a distinct shape, allowing gnarly roots to rise from bare dirt or moss as an important, ancient, even showy part of the tree. The line can be a shallow trench, metal edging, bricks, or monkey grass, doesn’t matter as long as it looks purposeful. When leaves fall, just blow them back underneath the tree to replenish the soil. 

Planting beneath mature trees can be a challenge, aside from the difficulty of digging organic matter into soft spots between tree-size roots. There’s not much opportunity to provide a good start to whole new plants in need of their own elbow room, and you only get one shot at it, so do the best you can (hint: it’s easier a day after a good soaking rain).

As for plants, there aren’t a lot that can tolerate the heavy shade and competition for root room and moisture; some aren’t fashionable or can be invasive without a border.

The most commonly planted and attractive low-growing groundcovers I see thriving under mature trees in older neighborhoods include English ivy, Vinca major, Liriope, mondo grass, Asiatic jasmine, moss, and Ajuga. There are others, but these reign the roost.

Trouble is, the plant approach takes time; the old horticultural adage is “first year they sleep, second year they creep, third year they leap.” Meanwhile, add a few clumps of taller shade plants like ferns, aspidistra, hosta, daffodils, and azaleas or other small shrubs, plus a bench, chairs, urn, birdbath, driftwood, or other “hard” feature to provide instant appeal. 

Whatever you do, please remember that those bark-covered behemoths are the shoulders of far-reaching arms and are important to the tree. Important enough protect and celebrate, rather than hide.