Black Walnut
Juglans nigra

Location in Ontario

Black Walnut is a Carolinian Tree that grows throughout the Carolinian Zone of the Deciduous Forest Region, but is frequently planted beyond its natural range. Black Walnut grows on well-drained, rich soil.


Black Walnut on Long Point, Norfolk County
 

Genus Juglans
Walnuts as a genus have compound, alternate leaves with 11 to 23 leaflets. They are monoecious with male (pollen) flowers and female (seed) flowers on the same tree. Large, edible nuts are produced. The wood is treasured for the colour and grain. In Ontario, Black Walnut and Butternut (White Walnut) can be found.

How Can You Tell Walnuts apart??
Black Walnut bark has dark furrows, Butternut is lighter with flat-topped ridges. Black Walnut leaves have smaller bottom leaflets, and the top leaflet is often missing. Butternut leaflets get narrower along the leaf. Walnuts are round, Butternuts are oblong and pointed.

In the Landscape
Black Walnut is a medium sized tree that grows to 30 metres with wide spreading branches. They can live to be over 200 years old. Black Walnut requires a lot of space. As a shade tree, it has a relatively open crown and leaves that tend to drop early. Black Walnut also produces abundant large nuts that will require clean-up.

TREE FACT: "Juglone", a chemical found in the leaves, bark, nut husks, and roots, and in the soil around Black Walnut trees, is toxic to some species of plants.


Black Walnuts in flower, Port Rowan

Leaves
Black walnuts have compound leaves, with 15 to 23 leaflets. Leaves turn yellow in the fall.
Bark
The bark is light brown with crossing ridges.
Flowers
Black Walnut is monoecious with male (pollen) flowers and female (seed) flowers on the same tree.  Pollen flowers are small and green, and found in long catkins. Seed flowers are in clusters at the end of a new shoot. Flowers appear in May with the leaves and are pollinated by wind.
Fruit
The fruit is an edible, round, hard nut with a green husk. Store-bought walnuts come from a different species of Walnut not native to Canada. Fruit appears in the summer and falls in October. Nuts are produced most years after 15 years of growth.

Wood
Black Walnut wood is medium hard, and is used to make cupboards, flooring and boats. It is prized for its beautiful dark colour and grain.
Specific gravity: 0.55
Janka Hardness: 1010 lb
Wood Comparison Chart


Large Black Walnuts, Norfolk County

Link to United States Forest Service Silvics Manual for Black Walnut.

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