Juglans californica aka California Black Walnut

Juglans californica is the California walnut, also called southern California walnut. It belongs to the walnut family, Juglandaceae. Its native range lies in southwest California, from Santa Barbara to San Diego. This deciduous tree grows in oak woods and along rivers. It also lives on bottomlands with moist or dry gravelly soil. It can form the canopy of a woodland garden and attracts wildlife.

Sources give heights from about 20 to 40 feet [6–12 metres]. Some trees look like shrubs where trunks divide near the ground. A short trunk supports a rounded crown. Several trunks can give the tree a broad V-shaped form. Gray or brown bark has shallow cracks and scaly ridges. Stout green twigs turn reddish brown as they age. The tree develops a deep taproot and dislikes root disturbance. Plants For A Future reports lifespans of about 125–150 years.

The leaves grow in an alternate pattern along the stems. Each pinnate leaf has nine to fifteen narrow leaflets. Their edges have fine teeth, and their tips taper. The upper face shines green, while the lower face looks paler. Leaves turn yellow or brown before they fall. Flowers appear with new leaves in spring, from April to May. Each tree bears both male and female flowers. Male flowers hang in yellow-green catkins on older twigs. Tiny female flowers grow near the tips of new shoots. Wind carries the pollen, and the tree is self-fertile.

Round nuts ripen in autumn within thin husks. These husks start green, then turn brown. The small, sweet seeds have thick shells. People eat them raw or cooked and add them to baked foods. The seeds also yield edible oil, which can spoil quickly. Plants For A Future lists no known hazards. It records a traditional use of leaf tea as a blood tonic. The tree also serves as rootstock for English walnut. Its branching trunk limits the use of its wood.

Grow this walnut in full sun, sheltered from strong winds. Deep, well-drained loam suits it, though it accepts other soil textures. Plants For A Future prefers moist soil; Oregon State says irrigation is unnecessary. Sources place hardiness within USDA zones 7–10; Oregon State specifies zone 8. Young plants need cold protection. Rain can wash growth-inhibiting chemicals from leaves into soil below. This can reduce the growth of nearby plants.