It’s difficult to plant anything under my maple tree because of the abundance of roots right at the surface. Can I add 6 inches of soil on top of the roots and plant in that?
Most trees have limited tolerance for changes in the soil grade over their roots. Either adding or removing soil in the root zone can weaken or kill a tree. Six inches is enough to smother many trees; I don’t recommend it. Even if the tree survives the added soil, it will immediately send its roots upward into the new soil layer and you’ll be back where you started.
Shallow-rooted trees like maples are a special challenge for gardeners. One landscaping solution is to choose a drought-tolerant, shade-tolerant perennial groundcover to blanket the ground under the tree. Tolerance of dry soil is necessary because of root competition from the mature tree. Plant smaller specimens that can be tucked among the tree roots without damaging them. You can top the area with up to 2 inches of compost, or a mixture of compost and coarser mulch, to help the groundcover plants get established. Don’t forget to water regularly; even a drought-tolerant groundcover will need some help initially to complete with aggressive tree roots.
Another option: Spread organic mulch, like shredded bark, 2 inches deep under the tree, and then add a few containers for floral color. By giving the tree and the potted flowers separate root zones, you’ll ensure they don’t compete with each other. —Doug Hall