For releasing toxins that frequently kill off other plants, I never would have suspected such. I noticed many of these trees during lengthy runs
around forest preserves, which at least appear to peacefully coexist among several other deciduous trees and shrubs. Although the husks
were sometimes bothersome on runs, the pinnately compounded leaves offer a great deal of shade in the summer months.
Juglans nigra (Black Walnut, Eastern Black Walnut, American Walnut)
Hardiness Zones: 4-9
Height: 22-30-meters (75-100 feet) (sometimes up to 40 meters (130 feet)) at maturity)
Diameter: 22-30 meters (75-100 feet) at maturity
Growth Rate: Maximum growth rate is 90-120 centimeters (36-48) inches per year. Early growth is rapid.
Age: These typically live for 60-100 years, although some have survived up to 300 years under optimal conditions.
Root System: deep taproot and a large fibrous network of roots
Tolerates: drought, rabbits, flooding (moderately)
Problems (major): Because Juglans nigra produces juglones, these kill many plants nearby. These toxic compounds are found, at least to a lesser degree, in the bark and leaves as well. Walnut caterpillars and fall webworms can cause serious damage.
Problems (minor): Root rot, canker, leaf spot, dieback, bacterial blight, anthracnose, and aphids. The falling fruits’ husks may be troublesome in autumn. Intolerant of shade. Black walnut chips may prove harmful towards horses.
Poisonous: Juglans nigra produces a substance called juglone, which is highly toxic to a large number of plants and extends anywhere from 50 to 80 feet away from the main taproot. Juglones can poison tomatos, potatos, blackberries, blueberries, azaleas, laurels, rhododendrons, multiple species of pine, columbines, peonies, asparagi, Hydrangeas, lilies, Silver Maples, White Birches, Norway Spruces, Basswood, yews, lilacs, cabbage, peppers, eggplant, Petunias, apples, and more.
Soil requirements: moist, well-drained soils preferred (can withstand occasional droughts), grows on sandy, loam, clay, or sandy soils (sandy soils allows for greatest root development)
Air Requirements:not sufficiently researched (not specified, not particularly a city/street tree due to its roots and juglone production)
Watering requirement: medium
Sun requirement: full sun required
Cones (male): none
Cones (female): none
Leaves: Lanceolate and pinnately compounded, the leaves range 12-24 inches with 19-23 leaflets (but no terminal leaflet usually).
Flowers: Flowers from May until June. The female flowers appear in terminal spikes, whereas the male flowers are 3-5 inch long catkins.
Fruits: Begins significant production of fruits (nuts) around 20 years old, although reports have shown some to begin seed production as early as 4 years old.
Seeds require stratification: yes
Monoecious or Dioecious: monoecious
Other than producing the toxic juglone substance, the Black Walnut has several neat features. The large, green to black walnut husks contain (usually) 2 edible white seeds. Unlike most other members of the Juglans genus, the Black Walnut typically lacks a terminal leaflet. Both the bark/wood and the nuts are darker colors, hence the name “Black Walnut”. The wood is considered highly valuable and is used for cabinets and furniture. Unfortunately, this has led to excessive logging, severely reducing Black Walnut populations.
Frequently logged for its wood, which is highly valued.
Details of fruits, leaves, and leaflets
Opening fruits (nuts) among fallen foliage (one has split open, revealing where the seeds once lay) (Image © 2004 Susan Sweeney)
Showing the trunk, branching patterns, and foliage (photo by Jami Dwyer, uploaded 25 June 2006)
I do not own the rights of these images; all credit goes to its original creator(s).