Tree Roots Lifting Block Patio
Q: "What can we do about tree roots pushing up through our patio blocks?"
We have a block patio next to our house, and we also have a honey locust tree that gives us filtered light in the summer. The roots seem to be pushing up the patio blocks. What can we do to repair it? And what kind of tree could we get to replace the honey locust that would shade the house and give us the same filtered summer light, but with less upkeep?
Michael; Coloma, MI
Roger Cook replies: The lifting of the patio blocks indicates that there's probably loam or sand underneath, and the roots are finding it. One option would be to take out the patio blocks, dig out 8 to 10 inches of the material, and install pack material under them instead. Pack material is a combination of stone and stone dust, and it discourages roots. You can find it in quarries and stoneyards.
The other option is to install a barrier to the roots. Barriers are often used when planting trees in sidewalks, or to rein in bamboo, and you can find several types on the Web. Installing one would involve digging a trench around the patio, cutting the roots, and installing the barrier. Before you backfill the trench, use a small pruning saw to cut off the roots cleanly so they'll heal quickly. Before I cut any roots, though, I would consult a certified arborist to see if it would compromise the tree's stability.
Another possibility is replacing your block patio with a wooden deck at ground level, supported by posts buried deep in the ground. The posts would be unaffected by the roots.
Removing the tree is the final option, but what to replace it with? The locust is a great tree for areas near people — it leafs out late, allowing early spring sun to warm the patio below. Its canopy is light, creating dappled shade in the summer. Its leaves simply disappear in autumn when they fall. It's long-lived, disease-free, and has an interesting shape and color in winter. What more could you ask of a tree? I'd explore all my other options before I removed that tree, because there are no suitable replacements.