Content Detail

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.  

This species is native to the Chicago region according to Swink and Wilhelm’s Plants of the Chicago Region, with updates made according to current research.

  • Family (English) Walnut
  • Family (botanic) Juglandaceae
  • Planting site City parkway, Residential and parks, Wide median
  • Tree or plant type Tree
  • Foliage Deciduous (seasonally loses leaves)
  • Native locale Chicago area, Illinois, North America
  • Size range Large tree (more than 40 feet)
  • Mature height 50-75 feet
  • Mature width 30-50 feet
  • Light exposure Full sun (6 hrs direct light daily)
  • Hardiness zones Zone 4, Zone 5 (Chicago), Zone 6, Zone 7, Zone 8, Zone 9
  • Soil preference Alkaline soil, Moist, well-drained soil
  • Tolerances Alkaline soil, Clay soil, Occasional drought, Road salt
  • Season of interest early fall
  • Flower color and fragrance Inconspicuous
  • Shape or form Round
  • Growth rate Moderate
  • Transplants well Yes
  • Planting considerations May be difficult to find in nurseries, Messy fruit/plant parts
  • Wildlife Cavity-nesting birds, Game mammals, Songbirds
  • Has cultivars Yes

Native geographic location and habitat:

Black walnut is native to much of the Eastern United States.C-Value: 5

Bark color and texture:

The 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. A leaf is one to two feet long. The leaflets are toothed and aromatic when crushed. Leaf color is green in summer, changing to yellow in fall.

Flower arrangement, shape, and size:

The flowers are Inconspicuous. The male flowers will be in drooping clusters and the female flowers in terminal spikes.

Fruit, cone, nut, and seed descriptions:

The fruit is a yellow-green, rounded husk, up to two inches in diameter and contains an edible nut.

Plant care:

Black walnut falling fruit is a potential safety hazard and can cause yard litter as well as staining on sidewalks. Produces a chemical, juglone, which is toxic to many plants. They are difficult to transplant due to a deep taproot. 

Do not prune in spring as black walnut is a ‘bleeder’ (sap will run from wounds). Black walnut should be pruned in the dormant season.

List of pests and diseases:

Black walnut is targeted by walnut and yellow leaf caterpillars. It is susceptible to anthracnose, which may lead to late summer defoliation. Thousand canker disease is a serious problem occurring in some states (not yet reported in Illinois). It is tolerant of high pH soil and shows some tolerance of salt.

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