Common Name: Californian White Oak

General Information

Quercus lobata is a deciduous tree with a very broad, much-branched crown when grown in the open; it usually grows from 10 - 25 metres tall but sometimes reaches up to 35 metres. The bole is typically 50 - 70cm in diameter, but diameters up to 280cm have been recorded[, ].
The seeds are harvested from the wild for local use as a food, and were a staple food for various N. American native tribes. The plant is also harvested for local use as a medicine and source of materials, and is harvested on a commercial basis for its wood. It is sometimes grown as an ornamental.

Known Hazards

All parts of the plant contain tannins. Whilst tannins are found in many foods, and have a range of medicinal uses. They are usually only present in low concentrations. In some foods made from oaks (particularly the seeds), the tannin content can be quite high unless the food is treated to reduce tannin content.
Tannins are only of low toxicity and, because of their bitter taste and astringency, are unlikely to be eaten in large quantities. However, if they are taken in excess, they can cause stomach pains; constipation followed by bloody diarrhoea: excessive thirst; and excessive urination[].

Botanical References

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Range

South-western N. America - California

Habitat

Fertile lowlands in deep rich soils of valleys[, ]. Valley floors and moderate slopes, open grasslands, savannah and oak woodlands, riparian areas in chaparral; at elevations up to 1,700 metres[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Deciduous Tree
Height	20.00 m
Growth Rate	Slow
Pollinators	Wind
Cultivation Status	Wild

Cultivation Details

Quercus lobata is a moderately cold-hardy tree, tolerating temperatures down to around -15°c when dormant. It grows best in areas with hot summers. In areas with cooler summers, such as the maritime regions of the temperate zone, it often grows poorly, failing to properly ripen its wood and suffering frost damage over the winter[, ].
Prefers a sunny position but can tolerate some shade[] - young plants tolerate reasonable levels of side shade[]. Prefers a good deep fertile loam which can be on the stiff side[, ]. Tolerates moderate exposure, surviving well but being somewhat stunted[]. Tolerant of seasonal inundation of the soil[]. Established plants are drought tolerant[].
A fairly long-lived tree in the wild, with specimens 300 - 400 years old recorded[]. It is very slow growing in Britain, but there is a specimen at Kew that was 27 metres tall in 1988[]. The tree flowers on new growth produced in spring, the seed ripening in its first year[, ]. Good crops are produced in the wild every 2 - 3 years[].
Mature trees have a thick bark and can survive most forest fires. Younger plants will often resprout from the base if top-killed by fire[].
Seedlings soon develop a taproot and become intolerant of root disturbance, they should be planted into their permanent positions whilst young[].
Hybridizes freely with other members of the genus[].
Plants in this genus are notably resistant to honey fungus[].

Edible Uses

Seed - cooked[]. A staple food for several native North American Indian tribes[]. The light brown, oblong or fusiform seed can be 30 - 60mm long and 12 - 25mm wide[]. The seed of this species is sweet and low in tannin and needs little if any leeching[, ]. The seed can be roasted and then eaten, its taste is something like a cross between sunflower seeds and popcorn[]. The seed can also be ground into a powder and used in making bread etc[].
In some species, especially many of those classified as 'white oaks', the seeds are low in tannins and have a more or less sweet and agreeable flavour. The seed of most species, however, have a very bitter flavour, due especially to the presence of tannins. In these species there are various processes that can remove or at least reduce the amount of these bitter substances (although other water-soluble substances, including some minerals, will also be removed).
Tannins are water-soluble and therefore the easiest way to remove or reduce tannin levels is by soaking in water. A few different methods are listed:-
A traditional method of preparing the seed was to bury it in boggy ground overwinter and allow the wet soil to gradually leach the tannins. The germinating seed was dug up in the spring when it would have lost most of its astringency and bitterness.
Another method was to wrap the seeds in a cloth bag and place them in a stream for several weeks.
Drying the seed and grinding it to a powder before soaking speeds up the process. The fastest method is to use hot water, by cooking the powder and changing the water several times until the cooking water is no longer bitter. Alternatively, you can use cold water (which is reported to produce the best quality flour). In this case, you soak the powdered seed in cold water for 12 - 24 hours then discard the water. Repeat this process for a number of times until the soak water is no longer bitter.

The roasted seed of many Quercus species has been used as a coffee substitute.

Medicinal

Quercus (oak) species are used in the traditional medicine of many cultures, being valued especially for their tannins. Various parts of the plant can be used, most frequently it is the leaves, bark, seeds, seed cups or the galls that are produced as a result of insect damage. A decoction or infusion is astringent, antibacterial, antifungal, antiseptic, styptic and haemostatic. It is taken internally to treat conditions such as acute diarrhea, dysentery and haemorrhages. Externally, it is used as a mouthwash to treat toothache or gum problems and is applied topically as a wash on cuts, burns, various skin problems, haemorrhoids and oral, genital and anal mucosa inflammation[]. Extracts of the plant can be added to ointments and used for the healing of cuts[, ].

A poultice of the ground galls and salt has been used as a treatment for burns, sores and cuts[].

A decoction of the bark has been used as a cough medicine and a treatment for diarrhoea[]. The pulverized bark has been used as a dusting powder to dry up running sores, it is particularly useful for babies with sore umbilicus[].

Other Uses

The leaves of most species in this genus are more or less rich in tannins. A mulch of the partially decayed leaves can be placed around vulnerable plants in order to repel slugs, snails, grubs etc, and these will in time break down to add humus and nutrients to the soil. Fresh leaves should be used with caution, however, since as these decay they utilize some of the nitrogen in the soil and thus can inhibit plant growth[, ].

Oak galls are excrescences that are sometimes produced in great numbers on the tree and are caused by the activity of the larvae of different insects. The insects live inside these galls, obtaining their nutrient therein. When the insect pupates and leaves, the gall can be used as a rich source of tannin, that can also be used as a dyestuff and is also used by many cultures to make ink[, ].
The bark of oak trees is also usually rich in tannins and can be used as a dyestuff and for waterproofing rope[, ].

The acorn meal has been used to mend cracks in clay pots[].

The wood is hard and fine grained but can be brittle and weak. It has a propensity to crack and warp while drying, and is often stained by fungus. These problems, however, can be overcome, and there is a small commercial market for the wood, which is used in cabinet making and to make wine barrels[]. It has also been used in ship building and keel blocks[].
The wood is a favoured fuel - burning well and giving off a lot of heat. It makes a good charcoal[, , , ].

Propagation

Seed - it quickly loses viability if it is allowed to dry out. It can be stored moist and cool overwinter but is best sown as soon as it is ripe in an outdoor seed bed, though it must be protected from mice, squirrels etc. Small quantities of seed can be sown in deep pots in a cold frame. Plants produce a deep taproot and need to be planted out into their permanent positions as soon as possible, in fact seed sown in situ will produce the best trees[]. Trees should not be left in a nursery bed for more than 2 growing seasons without being moved or they will transplant very badly.