Q: I would love to get some ideas on how to correct our uneven brick patio. The locust tree whose roots are causing the bricks to lift is not one we would want to lose, as it is our main source of shade from the hot southern sun. The tripping hazard is a concern as we are getting on in years, and someone told us it would not pass inspection when we go to sell. What should we do?
A: Brick paving generally fares better around trees than concrete because roots can break concrete and ruin it while bricks that lift can be taken out and redone. But the pictures you sent show a large area of brick paving that extends out from the tree in all directions. A few areas at the perimeter appear to still be flat, but the rest is an expanse of hills and valleys, thanks to the tree roots pushing up from underneath. Edges of bricks are sticking up and creating tripping hazards no matter which way you walk.
You don’t say what kind of locust tree you have, but the picture you sent shows roundish leaflets, a feature that distinguishes black locusts from honey locusts.
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Both types have compound leaves, with little leaflets extending from a central stem. Black locust leaflets, besides being rounder, have an uneven number on each stem, with a single one at the tip. Honey locust leaflets are all in pairs.
The Nebraska Forest Service describes black locusts as “one of the most adaptable and easy-to-grow trees for the urban landscape,” but warns against planting these in a typical yard. The roots are shallow and invasive, and the trees send out root suckers, meaning new trees can pop up where you don’t want them. In nonurban areas, trees and shrubs that spread via root suckers can be useful because thick stands stabilize steep banks. And locusts are especially helpful in these situations because they are legumes — pea-family relatives, which can move nitrogen from the air into nodules on their roots, enabling them and other plants to grow in poor soil.
Honey locusts also fix nitrogen from the air and thrive even in poor soil, but they don’t sprout from suckers. The Nebraska Forest Service says they usually do well where their root zone is restricted, making them useful in parking lot islands and along sidewalks. Honey locusts can have wicked thorns — up to eight inches long — and gummy seed pods that make a mess. But thornless, seedless cultivars have been developed. These are what nurseries sell for planting in urban areas.
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Of course, at this point, you don’t have a way of choosing which kind of tree to plant. You need to deal with the one you have. You might want to begin by having an arborist assess the tree, to make sure it is healthy and the roots aren’t damaging the foundation of your house. Keeping summer shade is a priority, but if the tree has problems that would make you need to remove it in a few years, it might be better to get started now on growing a replacement that’s more suitable for your yard.
Assuming the tree is a keeper, you need a solution that accommodates the root growth. Cutting the roots to create a level patio simply won’t work. You’d need to cut too many. And if the tree didn’t die, it would send out new roots, causing the problem to recur quickly.
Ruth Williams, a board-certified master arborist in Portland, Ore., said the issue is that the roots are growing bigger while soil under the pavers is shrinking. “Organic material in it is decomposing, but no new organic material is going in,” she said. The problem is especially acute close to the tree, where the roots flare out. She recommends pulling up the bricks there and expanding the planting area around the tree. For the rest of the patio, she suggests pulling up the bricks, adding sand, tamping that down to create a level surface, then replacing the bricks. “You might need to redo it every 10 years,” she said, but it would be the least expensive option and should protect the tree.
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The pictures you sent show that you have brick steps leading down to the patio, but the bottom step is not as high as the steps above. It looks like the steps were built first and then the brick patio was added, without taking into account how that would change the height of the bottom step. You may be used to that unevenness, but visitors are likely to trip. One solution would be to make the new patio height match the height of the bottom step, eliminating that tripping hazard. Even though a brick patio on a bed of sand allows water to drain through, it’s still a good idea to have the patio slope so heavy downpours drain where you want the water to go: away from the house, not toward it.
If you want a more long-lasting solution, you could consider replacing the patio with a low deck — really more of a platform than what you might think of as a deck — with an easy, non-trip way to get to it. If you make the deck height match the height of the second-to-last step as you descend, you could link the steps and the deck with a boardwalk.
You probably wouldn’t want a deck to be nearly as big as the patio is now. You could leave the bricks in areas where the paving is flat or remove all of them and replace them with gravel or mulch, or a combination. It’s important to let air still reach the tree’s roots, so avoid soil, which compacts too tightly to let air through.
However you redo the paving, don’t fret too much if a root or two gets damaged. “Locust trees are tolerant to construction damage,” Williams said. “They are tough as nails.”
Have a problem in your home? Send questions to localliving@washpost.com. Put “How To” in the subject line, tell us where you live and try to include a photo.
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