and Deciduous Forest Trees
of Southern Ontario

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 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.

Habitat: Black Walnut grows on well-drained, rich soil.

Landscape Use: Black Walnut is a medium sized tree, but has wide spreading branches and needs 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, and a chemical in the soil around it that inhibits growth of some plants.

Black Walnuts in flower, Port Rowan

Leaves: Black walnuts have compound leaves, with 15 to 23 leaflets.


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.

Fruit: The fruit is an edible, round, hard nut with a green husk. Fruit appears in the summer and falls in October. Nuts are produced most years after 15 years of growth.

Black Walnut nuts

TREE FACT: Walnuts sold in stores come from a different species of walnut that is not native to Canada.

Bark: The bark is light brown with crossing ridges.

TREE FACT: "Juglone", a substance found in the leaves, bark, nut husks, and roots, is toxic to some species of plants.

Size: Black Walnut is a medium sized tree that grows to 30 metres with wide spreading branches.

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. So many Black Walnut trees were cut down for wood that today large trees are scarce.
Specific gravity: 0.55
Janka Hardness: 1010 lb
Wood Comparison Chart

Large Black Walnuts, Norfolk County