Quercus

( KWER - kuss )

At-A-Glance Information

This genus is commonly known as Oak, and has a native range that is widely distributed across the Northern Hemisphere. Foliage is typically various shades of green and can be lobed or have spines or toothed margins. There are both deciduous and evergreen species in the genus, and they serve as keystone species in many different environments around the world. These slow-growing landscape trees and shrubs produce both male and female flowers in the same individual and acorns that follow take between 6 and 18 months to mature. Use oaks as landscaping trees in large gardens, or as shade trees. They can also be used as screens or windbreaks, and have very high wildlife value. Take care when planting Oak trees in the landscape, as plant parts are toxic to humans, pets and livestock if ingested.

Quercus Species and Varietals

The genus Quercus is a member of the plant family Fagaceae and includes 500 species. The trees in this genus are closely relatd to those in Castanea (Chestnut), Lithocarpus (Stone Oak), and Fagus (Beech). The genus name is derived from the Latin word kwerkwu, meaning 'oak'. The best growing zones for these classic landscape trees vary depending on the species grown. For more information, see the descriptions below. To find your zone, click here: Zone Map.

Quercus alba (White Oak, Eastern White Oak)
This deciduous species is native to eastern and central North America, and typically reaches about 80-100 feet tall when mature. Canopies can become quite massive. At higher altitudes, these plants tend to grow as large shrubs. Bark is ash-grey (very uncommonly white) and it peels somewhat when mature. These trees can live for 200-300 years and are suited for USDA hardiness zones 3-9.

Quercus aliena (Galcham Oak, Oriental White Oak, Hǔ Lì, 槲栎, Hú Lì, 槲櫟, Dà Hú Shù, 大槲樹, Naragashiwa, ナラガシワ, 奈良柏, Huli, 槲栎)
This deciduous species reaches 100 feet tall and has fissured greyish-brown bark. Leaves are hairy and grey-white on undersides. The wood is used in this tree's native range (Korea, Japan, China and Taiwan) for building boats and as flooring for houses. These trees can grow in partial shade to full sun, form deep taproots, and tolerates strong winds but not soggy soils.

Quercus arizonica (Arizona White Oak, Arizona Oak, Encino Blanco, Encino Azul, Encinillo, Mapaco, Rojaca-Sacamé)
This species is native to Arizona, New Mexico, Texas, and Mexico in the states of Sonora, Chihuahua, Coahuila, Sinaloa, and Durango. This is one of the largest southwestern Oaks and can reach up to 60 feet tall at maturity. These evergreen to semi-evergreen Oaks grow well in USDA hardiness zones 6-10.

Quercus austrina (Bastard White Oak, Bluff Oak)
This deciduous species of Oak is endemic to the southeastern United States and can reach between 45 and 60 feet tall when mature. Leaves are narrow, and these trees are tolerant to clay, sand, loam, acidic, and well-draining soils. They also have a high drought tolerance. Bastard White Oak grows well in USDA hardiness zones 8a-9b.

Quercus x bebbiana (Bebb's Oak, Bebb's Hybrid Oak)
This deciduous species is a naturally occurring species of Oak that is a cross between White Oak (Quercus alba) and Burr Oak (Quercus macrocarpa). These trees reach up to 50 feet tall when mature, and the acorns they produce are sweet enough to be palatable to humans. Bebb's Oak is suited to grow in USDA hardiness zones 3-8.

Quercus berberidifolia (California Scrub Oak, Scrub Oak, Barberry-Leaved Scrub Oak)
These plants form small evergreen to semi-evergreen shrubs and are native to California. They commonly reach between 3.5 and 6.5 feet tall (exceptionally to 13 feet in certain growing conditions). The specific epithet berberidifolia refers to the leaves, which are superficially similar to those of Barberry (Berberis) shrubs. California Scrub Oak is suited for USDA hardiness zones 7-9.

Quercus bicolor (Swamp White Oak, Bicolor Oak)
These deciduous trees are native to North America, where it grows rapidly to between 60 and 80 feet tall and just as wide at maturity. Foliage is green, and the bark is greyish-brown. It is an important species in lumber production, and is also widely grown as an ornamental tree. Swamp White Oak is suited for growing in USDA hardiness zones 3-8.

Quercus x bimundorum (Two Worlds Oak, Bimundor's Oak)
This deciduous hybrid is a cross between Quercus alba and Quercus robur. Trees typically reach about 40 feet in height and are widely used as garden ornamentals. They are suited for growing in USDA hardiness zones 4-8. Cultivars include 'Crimson Spire' (aka 'Crimschmidt' with a columnar growth form), 'Midwest' (aka 'Prairie Stature', with a pyramidal growth form), and 'Streetspire' (45 feet tall and 14-18 feet wide with a storm-resistant branching structure).

Quercus boyntonii (Boynton Sand Post Oak, Boynton Oak, Alabama Sandstone Oak)
This rare species forms a shrub or small tree. Plants are deciduous to semi-evergreen, and reach a maximum height of 20 feet. Leaves are green with large lobes. The species is considered critically endangered and is suited for USDA hardiness zones 7 and 8.

Quercus canariensis (Algerian Oak, Mirbeck's Oak, Zean Oak, Carvalho-de-Monchique, Carvalho-Argelino, Chêne Zéen, Zen, بلدياً الزان, Oued Zen, Tash’t Oak)
These Oaks are native to Portugal, Spain, Tunisia, Algeria, and Morocco. They are named for the Canary Islands, which they were once seen growing on, though they have since been extirpated. These are medium-sized deciduous to semi-evergreen trees that reach between 66 and 98 feet tall when mature and are suited for USDA hardiness zones 7-10.

Quercus chihuahuensis (Chihuahua Oak, Chihuahuan Oak, Felt Oak, Encino Miscalme, Encino Roble, Encino Blanco)
These deciduous to semi-evergreen Oaks are native to Texas and northern Mexico, and reaches about 33 feet tall. Leaves are entire to toothed and are green on top and yellow-grey and velvety underneath. Chihuahua Oaks are suited for USDA hardiness zones 8-10.

Quercus dentata (Japanese Emperor Oak, Daimyo Oak, Sweet Oak)
These deciduous trees are native to Japan, Korea and China and produce flowers in May, with acorns maturing from September to October. The species is suited for USDA hardiness zones 4-8. Trees reach between 66 and 82 feet tall at maturity, and have larger leaves than most other species in the genus. Cultivars include 'Pinnatifida' (pictured; with fernlike foliage) and 'Carl Ferris Miller' (to 26 feet tall).

Quercus depressipes (Depressed Oak, Davis Mountain Oak, Mexican Dwarf Oak, Encino Enano)
This species of live oak forms a shrubby evergreen bush that reaches up to just 1 to 3 feet tall when mature. These plants are found on grassy slopes along mountain ranges and are native to Mexico and the United States (Texas). Depressed Oak shrubs are suited for USDA hardiness zones 8 and 9.

Quercus douglasii (Blue Oak, Mountain Oak, Iron Oak)
Endemic to California, this species is the state's most drought-tolerant deciduous oak. These medium-sized trees have sparse foliage, and typically are single-trunked but can have multiple trunks, as well. Trees grow slowly, about a foot per year, and bark is light gray. Foliage is bluish-green and pollen is severely allergenic.

Quercus durata (Leather Oak, )
Endemic to California, this species of Oak produces leathery leaves, and forms a low-spreading evergreen shrub with rigid branches and deep green foliage. Great for hillside plantings in need of erosion control.

Quercus fabrei (Faber's Oak)
This species of Oak is deciduous, and is native to southern China. They can take the form of a large shrub or a tree that reaches up to 65 feet tall. Elongated leaves are serrated with small teeth, and are wider at the tip than the base.

Quercus frainetto (Hungarian Oak)
These deciduous trees can reach up to 125 feet tall and 66 feet wide, with a trunk girth of almost 7 feet. Bark is light grey and twigs are typically stout. Foliage is green and leaves are quite large (between 6-10 inches long). These are cultivated in larger parks and gardens due to their size, and the cultivar 'Hungarian Crown' is a choice variety with a handsome canopy.

Quercus gambelii (Gambel Oak, Scrub Oak, Oak Brush, White Oak)
This deciduous species is named for American naturalist William Gambel, and reach an average of 10-30 feet tall (exceptionally up to 60 feet). Branches are irregular and crooked, flexible enough to bend without breaking under heavy snow. Leaves are glossy and dark green, with pale velvety undersides. After fire, these Oaks quickly re-establish from root sprouts. Drought-tolerant.

Quercus garryana (Garry Oak, Oregon White Oak, Oregon Oak)
This deciduous species of Oak trees is native from California north through British Colombia. It is named for Nicholas Garry, the deputy governor of the Hudson's Bay Company. These plants can grow as trees or large shrubs, and can grow to reach 500 years old. Average tree height is about 80 feet tall (10-15 feet tall for shrubs), foliage is green and glossy,

Quercus germana (Mexican Royal Oak)
This semi-evergreen species is native to mountainous cloud forests in eastern Mexico, and produces a small to medium-sized tree reaching up to 40 feet tall when mature. It is a type of white oak, and produces green foliage with entire margins (not lobed or toothed).

Caring for Quercus

Take care when planting Oak trees in the landscape, as plant parts are toxic to humans, pets and livestock if ingested. Oak trees should be spaced 30 to 60 feet from each other (depending on their mature canopy size) and from buildings. When growing shrubby species as a hedge or tight windbreak, space plants 12 to 20 feet apart.

aks in the Black Oak Group, (Coast, interior, and Canyon Live Oaks, Shreve Oak and Kellogg’s Black Oak) are best pruned in the warmer, drier portion of the year: after the end of spring rains and before the fall rains begin. Roughly, late May/early June to mid-to- late-October is best. This is to avoid helping the pathogen, Sudden Oak Death, Phytophthora ramora –which seems to infect best in cool wet weather. If you have California Bays close to the above mentioned oaks, you might consider removing the California Bay touching the oak canopies or removing all branches that touch or shade any part of the oak canopies since the wet leaves of the Bays are excellent incubators for the active propagules of one of the reproductive stages of this aggressive organism.

Plant Ranunculus in a space in the landscape that receives full sun; ideally, they appreciate between 6 and 8 hours of sun each day for the best blooms. When these flowers are grown in less light, they will not flower as profusely. Ensure that soil is well-draining, rich in nutrients, and has a pH of between 6.0 and 7.0 (slightly acidic to neutral). If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. Apply a layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and to increase soil moisture retention. Water new plantings regularly as they establish a strong root system in their new home. At maturity, these plants perform well in consistently moist soils.

Fertilize yearly in early springtime with an application of 2 inches of compost around the base of plants. Pull mulch back before applying, work the compost gently into the soil a bit, water it in, and then replace mulch. Pruning is simple; remove any damaged, diseased, or dead foliage at any time during the growing season, and remove spent flower spikes to neaten up the appearance of plants and encourage reblooms.