California Walnut, Southern California walnut
Juglans californica
Family: Juglandaceae
What it is like
Juglans californica is a deciduous Tree growing to 6 m (19ft 8in) at a medium rate. See above for USDA hardiness. It is hardy to UK zone 8. It is in flower from April to May. The species is monoecious (individual flowers are either male or female, but both sexes can be found on the same plant) and is pollinated by Wind. The plant is self-fertile. Suitable for: light (sandy), medium (loamy) and heavy (clay) soils and prefers well-drained soil. Suitable pH: mildly acid, neutral and basic (mildly alkaline) soils. It cannot grow in the shade. It prefers moist soil.
Height (m): 6
Where it is found
Moist or dry gravelly soils along river courses and bottomlands. Locally common in oak woods below 750 metres.
South-western N. America - California.
Conservation Status:
Countries/locations it is found in
How it is used
Food
Rating: 2
Seed - raw, cooked or used in pies, cakes, biscuits, confections etc. A sweet flavour. The seed is small with a thick shell but it makes good eating and is said to have a better flavour than Juglans nigra. The seed is up to 15mm in diameter. The seed ripens in late autumn and, when stored in its shell in a cool place, will keep for at least 6 months. An edible oil is obtained from the seed, it tends to go rancid quickly.
Oil: Oil
Seed: includes nuts, cereals, peas and beans.
Medicine
Rating: 1
An infusion of the leaves is used to treat thin blood.
Blood tonic: Is this any different to a blood purifier?
Other
Rating:
This species is sometimes used as a rootstock for the common walnut, Juglans regia. Plants produce chemicals which can inhibit the growth of other plants. These chemicals are dissolved out of the leaves when it rains and are washed down to the ground below, reducing the growth of plants under the tree. The roots of many members of this genus produce substances that are toxic to many plant species, especially apples (Malus species), members of the Ericaceae, Potentilla spp and the white pines (certain Pinus spp.). Wood - moderately coarse-grained. An attractive wood, but the frequent branching pattern of the trunk limits the use of this wood commercially
Herbicide: Plants or plant extracts that can inhibit the growth of other plants.
Oil: Vegetable oils have many uses, as lubricants, lighting, soap and paint making, waterproofing etc. This does not include the edible oils unless they are also mentioned as having other uses.
Rootstock: Plants used as the rootstock for grafting scions onto.
Wood: A list of the trees and shrubs that are noted for having useful wood.
How it is grown
Requires a deep well-drained loam and a sunny position sheltered from strong winds. Prefers a slightly alkaline soil. Plants are not very hardy in Britain, tolerating temperatures down to between -5 and -10°c. A fairly fast-growing tree in its native habitat, but quite short-lived, dying after about 125 - 150 years. Plants produce a deep taproot and they are intolerant of root disturbance. Seedlings should be planted out into their permanent positions as soon as possible and given some protection since they are somewhat tender when young. Flower initiation depends upon suitable conditions in the previous summer. The flowers and young growths can be destroyed by even short periods down to -2°c, but fortunately plants are usually late coming into leaf. Any pruning should only be carried out in late summer to early autumn or when the plant is fully dormant otherwise wounds will bleed profusely and this will severely weaken the tree. Trees have a dense canopy which tends to reduce plant growth below them. We have no specific information for this species, but the roots of several members of this genus produce substances that are toxic to many plant species, especially apples (Malus species), members of the Ericaceae, Potentilla spp and the white pines (certain Pinus spp.). The leaves of many species also secrete substances that have an inhibitory affect on plants growing underneath them. All in all this is not a very good companion plant. Closely related to J. hindsii
Propagating it: The seed is best sown as soon as it is ripe in individual deep pots in a cold frame. You need to protect it from mice, birds, squirrels etc. The seed usually germinates in late winter or the spring. Plant out the seedlings into their permanent positions in early summer and give some protection from the cold for their first winter or two. The seed can also be stored in cool moist conditions (such s the salad compartment of a fridge) over the winter and sown in early spring but it may then require a period of cold stratification before it will germinate.
Best place to grow: Woodland Garden Canopy;
Habit: Tree
Hardiness: 7-10
Growth: Medium
Soil: Light (sandy), medium, heavy (clay)
Shade: No shade
Moisture: Moist