northern California black walnut

Photo: John Rusk from Berkeley, CA, United States of America — CC BY 2.0 · source

Survives zone 6 through 9

Harvest calendar

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

Northern California black walnut is grown less for its own small, thick-shelled nuts than as the classic rootstock underpinning the California walnut industry — it, and its Luther Burbank-bred hybrid with English walnut, 'Paradox,' support most commercial English walnut orchards worldwide thanks to their drought and nematode tolerance.

Hardiness

Zone 6–9

Habit

Tree

Edible part

Nut

Ripens

Sept–Oct

Mature size

Tree 10–23 m — not containerable

Light

Full sun

Soil pH

6.0–7.5 (near-neutral; lime-tolerant)

Environment

Temperate

Native range

Native to Northern California's Central Valley (Sacramento and San Joaquin Valleys), the inner northern Coast Ranges, and the San Francisco Bay Area, typically along streams and disturbed slopes at low elevations (0–300 m); some recent assessments extend its natural or naturalized range from southern Oregon to Southern California.

Status

Both wild and cultivated

Years to fruit

5–10 yrs

Growth speed

Documented mainly through its use as parent stock for the 'Paradox' rootstock, which Luther Burbank specifically selected for exceptionally fast growth, reflecting the vigor of the J. hindsii parent; precise annual height figures for the pure species are not well documented.

Spacing

1200 cm (472 in) apart — about 144 m² (1550 sq ft) per plant

Leaf shape

Pinnately compound leaves 22–45 cm long with 13–21 narrowly triangular to lanceolate leaflets, 5–12.5 cm long, with dentate margins and tufts of hair in the vein axils on the underside — a feature distinguishing it from the closely related J. californica.

Root system

Deep taproot present from an early age, which is why nursery and orchard stock is planted or grafted young and rarely transplanted once established.

Fruit description

A globose nut up to 3–5 cm across (kernel 2.4–3.2 cm) with a smooth, thick brown shell and a small, sweet kernel.

Propagation

Grown from seed, but because of its vigorous, disease- and drought-tolerant rootstock it is far more often propagated as seedling rootstock for grafting cultivated English walnut (J. regia) than for its own nuts. Seedlings develop a large taproot early and transplant poorly once established, so grafting or planting out is done while trees are young.

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.