Source: Rick Durham, horticulture extension professor  

Big shade trees are a gift — until their roots start showing in the lawn. Surface roots make mowing tough, trip people up and can heave sidewalks. They aren’t a sign your tree is failing, though. In most cases, they’re a normal response to how roots grow and how soil behaves. 

Most tree roots spread outward in the top 4–15 inches of soil because that’s where oxygen is available. In heavy, compacted, or poorly drained soil, oxygen is scarce, so roots creep even closer to the surface. Each year those roots thicken, the way a trunk does, and they can push through the turf. Erosion from rain and foot traffic exposes them more. Nearly any mature tree can develop surface roots, though poplars, willows, maples (Norway, red, silver), sycamores, aspens, beeches and some ash and pin oaks are frequent culprits. 

The worst thing you can do is cut or grind off visible roots. That invites decay and insects, removes thousands of feeder roots that absorb water and nutrients, and can weaken the tree’s stability. Piling on lots of soil is risky too; deep fill over the root zone can suffocate roots. 

First, consider adding a mulch layer over exposed roots. A two- to three-inch layer of shredded wood or chips cushions the roots, reduces mowing around the tree and holds moisture. Extend the mulch ring as far as you can — ideally to the dripline — and keep it pulled back a few inches from the trunk. Skip “volcano” mulching—don’t pile mulch around the trunk. If you want plants under the canopy, hand-dig small pockets within the mulched area for shade-loving perennials or groundcovers between roots; avoid rototillers and do not add thick layers of soil first.  Make sure plant roots extend down into the soil and not just into the mulch. 

Growing grass under trees is also an option but has its own challenges.  Even shade-tolerant species may not provide a thick enough cover to be attractive. The grass and tree roots will constantly compete for moisture and nutrients, and you may find yourself watering the grass under the tree more often than in other parts of the yard.  Nevertheless, if you want to try grass, rake away debris of sticks and excess leaves, then add just enough topsoil —a half inch or less — just enough to fill in between roots and smooth the surface. Seed with a shade-tolerant grass and water as needed. When mowing, you may want to set your mower deck a bit higher to avoid damaging any exposed roots. Because roots continue to thicken, expect to repeat this light topdressing every year or two rather than burying everything at once. 

Planning and planting choices help prevent the problem. In compacted or clay soils, select trees with deeper root systems such as black gum, ginkgo, yellowwood, zelkovas and many oaks are good options. You can also choose smaller ornamental trees whose roots are less likely to grow large enough to cause trouble. Plant slightly high (about two inches above grade), give trees room near pavement, and check local rules before planting along streets. Remember that roots extend well beyond property lines and will follow air, water, and space. 

In short, surface roots are mostly an aesthetic and maintenance issue — a response to soil conditions rather than a sign of poor tree health. Treat the soil gently, protect the roots, and manage the area with topdressing or mulch. Your tree will thank you — and your mower will, too. 

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