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Survives zone 7 through 9
Harvest calendar
Best planted in early spring after your last frost, or in fall before the ground freezes, depending on your climate.
A shrubby to small tree endemic to a handful of southern California foothill ranges, it is unusual among walnuts for resprouting from the root crown after fire or cutting, often forming multiple trunks. Its riparian and oak-woodland habitat has been so reduced by urban development around Los Angeles that the species is assessed as Near Threatened.
- Hardiness
- Zone 7–9
- Habit
- Tree
- Edible part
- Nut
- Ripens
- Sept–Oct
- Mature size
- Small tree 6–10 m, often multi-stemmed
- Light
- Full sun
- Soil pH
- 6.0–7.5 (near-neutral; lime-tolerant)
- Environment
- Temperate
- Native range
- Endemic to California, historically distributed through the Coast Ranges and interior valleys from the San Francisco Bay Area south through the Simi Hills, Santa Susana and Santa Monica Mountains to the San Jose, Puente, and Chino hills; surviving stands are fragmented, concentrated around the Santa Clarita River drainage and nearby foothill ranges, at elevations of roughly 50–900 m.
- Status
- Wild
- Years to fruit
- 5–10 yrs
- Growth speed
- Fairly fast while young — capable of reaching about 3.6 m (12 ft) within its first 10 years under favorable conditions, though growth slows with age; typical lifespan is around 100 years.
- Spacing
- 600 cm (236 in) apart — about 36 m² (388 sq ft) per plant
- Leaf shape
- Pinnately compound leaves 3.5–7.5 cm long overall — noticeably smaller than most walnuts — with numerous narrow, pointed leaflets.
- Root system
- Extensive root system, often including a deep taproot, suited to drawing on groundwater in canyon bottoms and streambank settings.
- Fruit description
- A globose nut up to about 1.5 cm across, enclosed in an indehiscent (non-splitting) husk, with a thick shell and a sweet-flavored kernel; nuts ripen in late autumn.
- Propagation
- Seed has no dormancy and germinates within about four weeks of falling naturally; nursery sources recommend sowing fresh seed immediately in deep pots in a cold frame protected from rodents, or cold-stratifying stored seed over winter for spring sowing. Trees begin bearing seed at 5–8 years of age, and western gray squirrels are a documented natural seed disperser.
- 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.
Growing guide
Fertilizing. Prefers a deep, well-drained loam, ideally slightly acid to neutral (pH 6–7), and does best on deep, clay-rich alluvial soils with good water-holding capacity such as canyon bottoms and alluvial terraces. No specific fertilizer program is documented — as a California native adapted to lean foothill soils it is not typically fed.
How it spreads. Unlike most walnuts, it resprouts vigorously from the root crown and trunk after cutting or fire, and in open savanna it often develops multiple trunks in a spreading 'V' form rather than a single stem; in denser stands it grows as a single-stemmed tree.
Growing tips. A chaparral and oak-woodland species that tolerates heat, smog, and drought once established but does best on mesic, north-facing slopes and streambanks; it is assessed as Near Threatened (IUCN) because its riparian and foothill woodland habitat has been lost to development around the greater Los Angeles and Ventura County area. Highly susceptible to crown rot caused by Phytophthora species, and heart rot commonly sets in from about 20–30 years of age, inviting termites and wood-boring beetles. It shows only intermediate to slight susceptibility to thousand cankers disease compared with the much more vulnerable J. nigra. It produces juglone, which suppresses germination of many nearby species, though tolerant native plants such as elderberry, wild rose, and sedges persist beneath its canopy.
Companion planting. Like other walnuts, likely produces some juglone (a root-zone compound toxic to sensitive plants like apples and blueberries), though this species hasn't been specifically studied for it — black walnut's spacing precautions are a reasonable default.
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