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TREES & Plants

Black walnut

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.

Botanical name: 
Juglans nigra
All Common Names: 
Black walnut, Eastern black walnut
Family (English): 
Walnut
Family (Botanic): 
Juglandaceae
Tree or Plant Type: 
  • Tree
Foliage: 
  • Deciduous (foliage falls off)
Native Locale: 
  • Chicago area
  • Illinois
  • North America
Hardiness Zones: 
  • Zone 4
  • Zone 5
  • Zone 6
  • Zone 7
  • Zone 8
  • Zone 9
Growth Rate: 
  • Medium
Light Exposure: 
  • Full sun (6 hrs direct light daily)
  • Partial sun (4-6 hrs direct light daily)
Tolerances: 
  • Occasional drought
  • Alkaline soil
  • Clay soil
  • Road salt
Soil Preference: 
  • Alkaline soil
  • Moist, well-drained soil
Flower Color & Fragrance: 
  • Inconspicuous
Size Range: 
  • Large tree (more than 40 feet)
Shape or Form: 
  • Rounded
  • Spreading
Landscape Uses: 
  • Specimen
  • Shade
Time of Year: 
  • Early fall
More Information: 

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).

Black walnut (Juglans nigra)
Black walnut (Juglans nigra)
photo: John Hagstrom

Disease, pest, and problem resistance

Tolerant of high pH soil.
Shows moderate resistance to salt.

Native geographic location and habitat

C-Value: 5
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.

Black walnut (Juglans nigra)
Black walnut (Juglans nigra)
photo: John Hagstrom

Fruit, cone, nut, and seed descriptions

Fruit is a yellow-green, rounded husk, up to 2 inches in diameter, containing an edible nut.