Monday, March 02, 2009
Strategies for landscaping around maples
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
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5102 Greenfield St. SW
Roanoke, Va. 24018
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Q: We have mature maple trees that we planted throughout the landscape of our home several years ago and need your suggestions regarding two major problems the maples are causing. We have a bluegrass and fescue lawn, and it is getting thinner close to the maple trunks. What can we do to thicken up the grass there? The other problem is that there are roots of the maples growing on the ground surface. I have been thinking that I would put some topsoil over those surface roots and grow some shade-loving flowers like impatiens or hostas under the maples this spring. What’s your opinion about doing this?
A: Thickening up the grass under a mature maple close to its trunk is a real challenge, and I make no guarantees.
Thin turf close to a mature maple trunk is the result of competition from the maple’s shallow root system, which is a natural characteristic of maples, plus the result from shade cast by the tree that limits photosynthesis or food production in turf plants.
Try limbing up the trees to let more direct sunshine to reach the grass. Winter or early spring before leaf buds emerge is a good time to take lower limbs back to their branch collar connection with the trunk. If the lower limbs are already big, which means greater than 3 to 4 inches in diameter at that location of connection, you or a tree cutting professional should leave the big growth alone. But side branches smaller than 3 inches in diameter from each lower limb can be pruned. You can cut all lower branches that are within 10 feet from the ground.
Nothing can be done about the shallow root system. Maple roots will out-compete turf roots for moisture and nutrients. You can try overseeding and watering the area close to each maple’s trunk with a fine fescue, which is the grass species that is adapted to dry shade. If you want grass in those areas, you will likely need to overseed close to each trunk at the appropriate seeding time at least every other year.
The easiest solution will be to place a shallow bowl or saucer-shaped ring of mulch around each maple trunk and extending out as far under the branches as you think your landscape’s appearance will allow. Kill any living grass or weeds in the area to be mulched by carefully spraying them with Roundup or a similar chemical. Wait seven days after spraying before mulching at a thickness of about 1/2 inch close to the trunks and 2- 1/2 inches farther away.
Don't waste your time spreading a thin layer of topsoil over the roots. Maple roots will probably surface again. And if you place a deeper topsoil layer -- say, 5 inches' worth -- you'll rot those roots.
Planting annual flowers close to each maple trunk is not recommended because annuals in that area will dry out quickly and require frequent irrigation, which could possibly cause rotting to the maple trunk.
Hostas, however, in scattered locations in the existing soil under each maple and away from their trunks, will add landscape interest to the area.
