black walnut

Photo: Unknown — Public domain · source

Survives zone 4 through 9

Harvest calendar

Best planted in early spring after your last frost, or in fall before the ground freezes, depending on your climate.

Black walnut is the classic North American nut-and-timber walnut, prized for its rich, bold, distinctly stronger-flavored oily kernel and dark cabinet-grade wood, but it is also the textbook case of juglone allelopathy — its roots, hulls and fallen leaves poison nearby tomatoes, apples and pines — and it is the species most severely threatened by thousand cankers disease.

Hardiness

Zone 4–9

Habit

Tree

Edible part

Nut

Ripens

Sept–Oct

Mature size

Large tree 22–35 m — not containerable

Light

Full sun

Soil pH

6.0–7.5 (near-neutral; lime-tolerant)

Environment

Temperate

Native range

Native to eastern North America, from Massachusetts south to Florida and west to Texas and Minnesota, growing in rich, fertile woods, hillsides and valleys on deep, well-drained soils.

Status

Both wild and cultivated

Years to fruit

5–10 yrs

Growth speed

Fast while young — commonly 60–90 cm per year — slowing to roughly 30–60 cm per year as the tree matures; trees generally reach fruiting maturity in about 10–15 years.

Spacing

900 cm (354 in) apart — about 81 m² (872 sq ft) per plant

Leaf shape

Alternate, pinnately compound leaves 30–60 cm long with 13–23 (occasionally up to 24) oblong-lanceolate leaflets with finely serrate margins, glabrous above and hairy beneath; the terminal leaflet is often reduced or missing. Bruised foliage gives off a strong, sweet, resinous smell distinctive to the species.

Root system

Develops a deep taproot — described as running straight down like a carrot — giving strong drought resistance once established, but making mature trees difficult to transplant.

Fruit description

A round nut 3–4 cm in diameter (around 17 g in wild trees, 20–30 g in cultivars), enclosed in a thick, indehiscent, pungent green husk that stains dark on contact. The shell itself is tough, thick and deeply, finely ridged — genuinely a hard nut to crack — protecting a rich, oily kernel (about 65% fat) with a bold, earthy flavor distinctly stronger than English walnut, though the pressed oil turns rancid quickly.

Propagation

Grown from seed sown as soon as ripe, one per deep pot in a cold frame, germinating in late winter or spring; seed can also be kept cool and moist over winter (e.g. in a refrigerator) and cold-stratified before an early-spring sowing. The deep taproot means seedlings should be planted into permanent positions while still young. Named cultivars are propagated by grafting or budding onto black walnut seedling rootstock.

Pollination

Monoecious but HETERODICHOGAMOUS — a 2nd cultivar of the opposite type greatly improves set

The edible parts listed above are a starting point, not a field guide. Identify a plant with certainty — ideally against a local authority — before eating any part of it, and read the full disclaimer. Spotted something wrong? Report it.