The black walnut is a Chicago-area native tree that provides excellent shade for large properties. It needs to be sited with care, since the tree produces a chemical that is toxic to some other plants. The fruit is a rounded, yellow-green husk, containing a nut that is a food source for squirrels. The black walnut also attracts the banded hairstreak butterfly, serving as a caterpillar host.
- Deciduous (foliage falls off)
- Chicago area
- North America
- Zone 4
- Zone 5
- Zone 6
- Zone 7
- Zone 8
- Zone 9
- Full sun (6 hrs direct light daily)
- Partial sun (4-6 hrs direct light daily)
- Occasional drought
- Alkaline soil
- Clay soil
- Road salt
- Alkaline soil
- Moist, well-drained soil
- Large tree (more than 40 feet)
- Early fall
Size and Form
50 to 70 feet high and 30 to 50 feet wide; rounded to spreading, irregular form
Tree & Plant Care
Falling fruit is a potential safety hazard and can cause staining on sidewalks and yard litter.
Produces a chemical juglone, which is toxic to many plants.
Difficult to transplant due a deep taproot.
Do not prune in spring as black walnut is a 'bleeder' (sap will run from wounds). Prune in dormant season.
Disease, pests and problems
Targeted by walnut and yellow leaf caterpillars.
Susceptible to anthracnose.
Thousand canker disease is a serious problem occurring in some states (not yet reported in Illinois).
Disease, pest, and problem resistance
Tolerant of high pH soil.
Shows moderate resistance to salt.
Native geographic location and habitat
Native to much of the Eastern United States.
Attracts birds & butterflies
The nut of the black walnut is a food source for squirrels.
Caterpillar host for the banded hairstreak butterfly
Bark color and texture
Bark is medium brown and has thick, interfacing ridges.
Leaf or needle arrangement, size, shape, texture, and color
Alternate, pinnately compound leaves with terminal leaflet often missing; leaf is 1 to 2 feet long; leaflets toothed; aromatic when crushed.
Leaves are green in summer, changing to yellow in fall.
Flower arrangement, shape, and size
Inconspicuous; male flowers in catkins in drooping clusters; female flowers in terminal spikes.
Fruit, cone, nut, and seed descriptions
Fruit is a yellow-green, rounded husk, up to 2 inches in diameter, containing an edible nut.