Q: I had to take out a dying flowering crab apple, thanks to a neighbor's walnut tree, which has poisoned the ground under its drip line. Is there a midsize tree that will survive under a walnut in Zone 5? — Sharon Nightingale, Bloomfield Hills, MI
A: It's the walnut's roots that produce most of the chemical that stunts the growth of other plants, and its roots extend considerably beyond the reach of its branches (the ''drip line''). Apples are notoriously sensitive, as you've learned. Fortunately, there are several beautiful small to medium-sized trees that are immune to walnut damage. Other walnut family members (Juglandaceae) include hickory (Carya) and wingnut (Pteracarya). For something that flowers in spring like your former crab, I suggest dogwood (any kind), eastern redbud (Cercis canadensis) or Carolina silverbell (Halesia carolina). All have beautiful flowers and are superb hardy small trees unfazed by nearby walnut roots. Other trees include fruiting cherries, red cedar, black locust, pawpaw and persimmon. Equally walnut-proof are Japanese maples, which form wonderful branch patterns and have a range of foliage colors and textures. 'Heritage' river birch (Betula nigra), which has buff-colored, peeling bark, will also be fine. Duraheat river birch is a good selection for Southern gardens. If you'd like to try an evergreen, consider either arborvitae (Thuja) or American holly (Ilex opaca).