Coast Live Oak is the most common oak and most common tree in our foothills and surrounding valleys. It is an imposing of majestic size, with a dense, wide that often reaches all the way to the ground. It provides food and shelter for a host of different animals. You can recognize it by its silhouette, its long, slim acorns, and its leathery, spiny leaves that are cup-shaped when you turn them upside down. This oak can get quite old, reaching ages of 100, 200, and even 500 years.

Leaves: The leaves are 1 to 2 1/2 inches long, and two-thirds as wide. Young leaves are either light green or reddish-brown, sometimes almost pink when they first emerge. Mature leaves are hard and leathery, and dark green above. The leaf underside is lighter green, and our local (var. agrifolia) has tiny, hairy tufts in the vein . (Some say it has “hairy armpits”.)

The leaf edge is weakly spiny and the leaf curves down at the outer edges. When you turn the leaf over, it looks like a miniature bowl or cup. Leaves least exposed to the sun, growing in the shade of other leaves, are generally larger, thinner, and flatter than those in the outer crown of the tree. Oaks have and on the same tree. The male flowers are borne in that are 1 to 2 1/2 inches long and often develop in bundles. The single, tiny female flowers are only about 1/8 inch long and appear in leaf axils on very short stalks. You will seldom see them, unless you look very closely and know what you are looking for. Flowering is generally from March to May. The fruit is an acorn that consists of a slender, pointed nut in an acorn cup. The nut, 1 to 1 1/4 inches long, is first green, then matures to dark brown. The thin, flat scales on the outside of the acorn cup, and the slender shape of the nut, help distinguish this species from other oaks. After the acorn ripens, the whole acorn (nut and cup) drops off or is taken by animals, and usually no empty cups remain on the tree.

Oak Apple: The big, round mass that resembles an apple is not a fruit, but an insect . A tiny Live Oak Apple Gall Wasp (Callirhytis quercuspomiformis) lays its eggs in a bud of a twig. Secretions from the wasp larvae cause the twig to expand and grow into a mass that protects the developing larvae. This mass has a relatively smooth surface and, when fresh, is green or red, often making it look like an apple. As it ages, it fades to beige. Galls generally do not harm the tree. Several small holes in the gall indicate that the wasps have eaten their way to the surface and flown away as adults. Coast Live Oak grows generally below 3,000 feet, but occasionally up to 5,000 feet on slopes, in valleys, and in oak woodlands. This oak grows in most of California’s and in the and , as well as in . It is also widely planted. Coast Live Oak belongs to the , or Red Oak, group and is closely related to Interior Live Oak (Quercus wislizeni). Other local oaks are Leather Oak (Q. durata) and Engelmann Oak (Q. engelmannii), in the White Oak group, and Canyon Live Oak (Q. chrysolepis), a member of the Golden Oaks. All are shown in this interpretive guide.

California Black Oak (Q. kelloggii) grows at higher elevations in the San Gabriel Mountains, as does Chinquapin (Chrysolepis sempervirens), another member of the Oak family. On the desert side, Tucker’s Oak (Q. john-tuckeri) can be found, while the range of Valley Oak (Q. lobata) extends only to the western edges of the San Gabriels. This mature oak demands space, as it grows wider than tall. It is slow-growing, about 40 feet in the first 20 years, then slower still. A Coast Live Oak offers prime to very many birds, insects, reptiles, and mammals. For a large landscaped area, this is a favorite choice, when considering majestic beauty and environmental benefits. Oaks give shade, are quite fire resistant, provide habitat, and cool their environments.

If you need to prune, we recommend that you engage an oak tree specialist and check local tree ordinances. Pruning should only be done in summer (mid-July to September), and is usually needed only for young trees. Over-watering a Coast Live Oak in summer may kill it by encouraging the growth of Oak Root Fungus, but it can take up to 10 years to see the effects of inappropriate watering. Then it is usually too late to remedy the situation. In years with low rainfall, provide extra water, but only in winter (November through April). Compaction of the soil, from the trunk out to the drip line, can also be detrimental to the tree. Avoid high traffic directly under a tree; a bench, however, is fine and makes a great birding spot.

If you choose to plant other plants under an oak, use plants that don’t require summer water. A number of good choices are available.
Full sun.
No summer water to occasional.
Can tolerate clay soil. Acorns are eaten by Mountain Quail, California Quail, California Towhee, Band-tailed Pigeon, Oak Titmouse, Scrub-Jay, Steller's Jay, Spotted Towhee, Acorn Woodpecker, White-breasted Nuthatch, and California Thrasher. In addition, the catkins are eaten by Oak Titmouse, Acorn Woodpecker, and Lesser Goldfinch. Coast Live Oak is a for California Hairstreak, California Sister, Propertius Duskywing, and Mournful Duskywing. The bark of Coast Live Oak is fire resistant, so the above-ground parts of the tree usually survive fires, even though the leafy crown may be burned. If not too badly burned, the tree will sprout new growth from the trunk and branches, rather than from the roots. New trees may grow from acorns that were buried in the soil by animals, but acorns are sensitive to heat and most do not after a fire. Quercus is the Latin name for oak; agrifolia is a variation of aquifolia, “sharp-leaved”, referring to the sharp spines on the leaves.

The common name Live Oak is used throughout the United States for oaks that are evergreen. Coast in the name refers to the fact that this species grows between the ocean and the western or southern slopes of the coastal mountain ranges.