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Tree roots in your lawn

What to do with bumpy roots

By: Sandy Feather©2010
Penn State Extension

Q. I have a sweet gum tree in my front yard that has such severe surface roots that it is difficult to mow the grass. Is it okay to cover them with soil and replant the grass?
  A. Those surface roots are technically a tree’s lateral roots, and they often grow near the soil surface. They function in the transport of water and nutrients, and are important to anchor the tree to the ground. Sinker roots - roots that grow straight down into the ground - grow off of lateral roots. Although certain species of trees seem to cause more of a problem with surface roots than others, most large, older trees will produce some surface roots.
It is a common misconception that tree roots grow very deep in the soil. Most tree roots are found in the top six to eighteen inches of soil. As the tree grows in height and diameter, so do the roots, which eventually brings them to the surface.

Surface roots in a lawn from a Silver Maple tree
Silver Maple is one of the most notorious
trees for bumpy lawn surface roots

Some of the tree species that are notorious for producing surface roots are those that grow quickly. These include: Norway maple (Acer platanoides); red maple (Acer rubrum); silver maple (Acer saccharinum); tree-of-heaven (Ailanthus altissima); alder (Alnus spp.); river birch (Betula nigra); hackberry (Celtis spp.); American beech (Fagus grandifolia), thornless honeylocust (Gleditsia triacanthos var. inermis); European larch (Larix decidua); sweetgum (Liquidambar styraciflua); dawn redwood (Metasequoia glyptostroboides); mulberry (Morus spp.); Colorado spruce (Picea pungens); sycamore or London plane tree (Platanus spp.); poplar (Populus spp.); pin oak (Quercus palustris); black locust (Robinia pseudoacacia); willow (Salix spp.); elm (Ulmus spp.) bald cypress (Taxodium distichum); and linden (Tilia spp.). Many of these are trees that tolerate adverse growing conditions. Their propensity for producing surface roots aids in their survival in such situations.

Under the right conditions, any species of tree can produce surface root systems. Environmental factors play an important role in the growth of surface roots. It is easier for roots to grow close to the surface when a tree is grown in hard, compacted clay soil or in areas where the soil is saturated with water frequently. Roots tend to grow where they find the most favorable conditions: adequate water, air and nutrients. In poor growing conditions, the most favorable place is often close to the soil surface. Also, erosion can expose a tree's lateral roots.

What about covering roots with soil?

Even if you cover them with soil and reseed the area, those roots will just grow back up to the soil surface as they continue to grow in diameter. It is not a good practice to place additional soil over the root system of any tree, because roots need oxygen. If they are buried too deeply, they literally suffocate, and the tree will decline and die over time.

Sometimes people ask if it is okay to cut those roots – the short answer is “no.” Removing those roots can injure and weaken a tree, making it more susceptible to insect and disease problems. More importantly, it creates a hazardous situation since those roots support the tree, making it more likely to come down in a storm or under a load of snow.

Finally, continually running over those surface roots with a lawn mower is not a good idea. The mower wounds them, creating an entrance into the tree for insect problems and/or disease-causing organisms. Besides, it's hard on the lawn mower and you!

Groundcover around a tree
Pachysandra groundcover around the base of a Pin Oak

The simplest solution is to replace the grass with mulch or a ground cover such as goldenstar (Chrysogonum virginianum), barrenwort (Epimedium), creeping lily-turf (Liriope spicata), Allegheny spurge (Pachysandra procumbens), Japanese spurge (Pachysandra terminalis), creeping myrtle (Vinca minor), or barren strawberry (Waldsteinia ternata).


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