Black Walnut

Size, growth and what to expect

Young black walnuts on the best ground put on three to four feet of height a year. Our growth estimator models the tree at nearly three feet a year, its rate for a fast grower. In a yard expect 70 to 100 feet, while forest trees on the best sites reach 100 to 120 feet with trunks 30 to 40 inches through. The crown spreads 30 to 50 feet. Trees typically live 150 years, and the oldest known has been ring-counted to 260.

An open-grown tree may drop a few nuts at 4 to 6 years old, but large crops wait until 20 to 30 years. The best bearing starts around 30 and continues for another 100 years, with a good crop perhaps twice in 5 years. Each nut sits in a round green husk up to 2 inches across. Nigra means black, for the dark bark and the stain the nuts leave.

It grows wild as scattered trees from Vermont and Massachusetts west to southern Ontario, Minnesota and Nebraska, and south to Oklahoma and central Texas.

How to grow Black Walnut

Black walnut wants full sun and deep, average soil that drains, ground that grows good corn. At full size it needs 50 feet from the house and the vegetable garden. Set trees 30 to 60 feet apart.

Plant while dormant, between leaf fall and bud swell. Saplings ship bare-root or in tall pots that keep the taproot straight. Dig wide but no deeper than the roots, hold the root flare at grade, and backfill with what you dug. Sow nuts in fall, husks off, two inches deep under pinned hardware cloth, or squirrels take them all.

Water weekly through the first summer when rain is short, and mulch a wide ring off the bark. Voles girdle young walnuts under snow, so sleeve the stem until the bark roughens, and cage against deer. Prune in late summer, because spring cuts bleed.

A lone black walnut can set nuts from its own pollen, but its catkins usually shed when its own flowers are not ready. A second walnut nearby improves the crop. The taproot goes down fast, so plant small trees and leave them be. Roots, husks and leaves release juglone, which kills tomatoes, potatoes, apples and blueberries nearby. Anthracnose drops leaves early in wet summers. Thousand cankers disease has reached the East; watch for a crown thinning from the top. Seedlings usually bear their first real crop at around ten years.