How to spot black walnut
- Long compound leaves with 15–23 leaflets
- Round green husks (walnuts) that drop and stain everything in fall
- Dark, deeply furrowed bark on a tall, straight trunk
- Often the tree nothing will grow under
Black walnut is one of the most common large trees across the Philadelphia area, and a bit of a love-hate tree. The wood is valuable, but the nuts are a slippery, staining mess in fall, and the roots release juglone — a natural compound that stunts or kills tomatoes, azaleas, and a lot of other plants growing nearby.
Because they get big and heavy, our walnut calls are usually about limb reduction over the house, cleanup, or removing one that's outlived its welcome in a small yard.
Common problems we see on black walnut
This is general guidance from three decades of tree work across the Philadelphia area — not a formal diagnosis. When it matters, we'll come look at the actual tree and give you a straight answer, free.
Brennan Tree Service has cared for trees across the Philadelphia area since 1994.
Frequently asked questions
Why won't anything grow under my walnut tree?
Black walnut roots release juglone, a natural chemical that's toxic to many plants — tomatoes and azaleas especially. It's not your gardening; it's the tree. We can help if you're deciding whether the tree's worth keeping.