Black Walnut

Site & soil

Plant black walnut in full sun, with six or more hours of direct light. It tolerates partial shade but grows and bears best in full sun. It does best in deep, well-drained, medium-textured soil and tolerates a wide pH range, roughly 4.6 to 8.2. Water needs are moderate once the tree is established, but young trees need watering during dry spells. It requires 1,400 or more chill hours, which West Virginia winters provide.

Companion planting

Plants that struggle under a walnut are often responding to dry soil and low light, which occur under any large canopy (Iowa State Extension). Juglone does affect a short list of sensitive plants, which are best kept out of the root zone:

• Tomatoes and related plants, including peppers, potatoes, and eggplant
• Apple and crabapple
• Blueberries

Many trees and shrubs tolerate juglone. Penn State Extension lists pawpaw, persimmon, oak, black cherry, eastern redbud, serviceberry, hickory, hazelnut, elderberry, black raspberry, and currant, which together cover much of a food-forest understory.

Spacing

Mature trees reach up to 100 ft tall with a 50 to 70 ft spread. Space trees 30 to 60 ft apart, and keep them well away from buildings, septic lines, and areas where heavy shade would be a problem in the future.

Pollination

Black walnut is wind-pollinated. A single tree can pollinate itself, but its male and female flowers usually open at different times (dichogamy), so a lone tree produces unreliable crops. Plant two or more trees for consistent nut production.

Planting

Black walnut develops a deep taproot early and is difficult to transplant once established, so plant it in its permanent location.

• Dig deep enough that the taproot points straight down without curling or bending.
• Set the tree at the depth it was growing, with the root collar level with the soil surface.
• Backfill with native soil and water thoroughly to settle the roots.

Clear a circle a few feet across around the trunk of grass and weeds, and mulch it, keeping mulch off the bark. Grass competition slows the growth of young walnuts significantly.

First-year care

• Water deeply and regularly through the first growing season, and during dry periods in the second.
• Keep the mulched circle free of grass and weeds all season.
• Protect the trunk from deer rubbing and vole damage with a tree guard or wire cage.
• Avoid heavy fertilizing in the first year so the tree puts its energy into root growth.
• Expect modest top growth in the first year while the taproot establishes.

Pruning

Prune in late winter, while the tree is dormant and the branch structure is easy to see. Train young trees to a single central leader: keep the strongest upright shoot and shorten or remove competing leaders. Remove dead, damaged, and crossing limbs, and raise the lowest branches gradually over several years rather than all at once. Keep cuts few and small on young trees.

Harvest

Trees typically produce their first nuts at 4 to 6 years, with full crops closer to 20 years. Nuts drop in fall.

Nuts are ready when the hull softens, turns from green to yellowish, and dents under thumb pressure. Gather them from the ground promptly and remove the hulls right away, because hull juice discolors the kernel and gives it a strong flavor. Wash the hulled nuts in a bucket of water and discard any that float, since floating nuts are usually unfilled.

Dry the nuts for two to three weeks before cracking, spread on a screen no more than three nuts deep in a cool, dry, well-ventilated place. Shelled kernels can be bagged and frozen for long-term storage.

Wildlife

Squirrels harvest a share of the nuts. Black walnut is also a larval host for the regal moth (whose caterpillar is the hickory horned devil), the luna moth, and the banded hairstreak butterfly.