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Saturday, December 29, 2018

Plant of the Month (December) : California Scrub Oak – Quercus berberidifolia

California scrub oak (Quercus berberidifolia): Mother Nature's Garden of Health,
Gardena, California

Limited gardening space requires thoughtful plant choices.  Good plants for smaller gardens combine beauty, usefulness and habitat value; what we like to think of as ‘value added’ plants.  Some of the best evergreen habitat plants are the native live oaks. They are also attractive and provide food (for those willing to process the acorns). And fortunately, several local live oaks are small enough to be considered for suburban gardens.  One of our favorites is Quercus berberidifolia.  The scientific name is pronounced: KWER-kus   ber-ber-id-i-FO-lee-uh.
California is blessed with twenty-one species of native oaks.  Of these, sixteen are native to Los Angeles County – a remarkable amount of oak biodiversity.  The Southern California oaks are mostly evergreen (thirteen of sixteen species).  And of the evergreens, only five (Quercus agrifolia; Q. chrysolepis; Q. engelmannii; Q. tomentella; Q. wislizeni) are large trees.   The rest are large shrubs or small trees, of a size suitable for smaller landscapes. 

California scrub oak (Quercus berberidifolia) vs. Nattall's scrub oak Quercus dumosa)

Among the smaller S. California live oaks, Quercus berberidifolia and Quercus dumosa (Nuttall’s scrub oak) are most widely available in the nursery trade. Like most oaks, the scrub oaks of California are prone to hybridization, producing a number of hybrid forms.  It’s likely that some plants available for purchase are actually hybrids.  And there’s still considerable debate about the range and characteristic morphology of these two species.  The interested reader is directed to references 1-6, below, for more on this evolving topic.  

Quercus berberidifolia is known by several common names: Inland Scrub Oak; California scrub oak; Scrub oak.  It belongs to the Family Fagaceae (the Beech Family) and is a member of the White Oak section of the genus Quercus. Its range extends from the Northern California coastal foothills to Baja California, Mexico. In Los Angeles County, it can be found in the Santa Monica and Verdugo Mountains and the foothills of the San Gabriel Range, below about 5000 ft. elevation.  It is most commonly associated with the chaparral plant community.

California scrub oak (Quercus berberidifolia):
 3 years in ground

California scrub oak (Quercus berberidifolia):
 4 years in ground

The California scrub oak is a small, evergreen or semi-evergreen shrubby oak.  When young, it has a somewhat scraggly appearance (above). With age, it develops its characteristic mounded form.  It typically grows no taller than about 9-10 ft. (to 3 meters), but may grow 15+ ft. in prime locations.  It often is slightly wider than tall: usually 15-20+ ft. wide.  It has light green-gray to gray, smooth bark.  The foliage is dense, making this a good screening shrub.  The reader is directed to references 7-9, below, for more photos.

Quercus berberidifolia is a slow growing plant, adding 1-2 ft. of new growth each year.  It’s also long-lived in the wilds – likely several hundred years.  It’s often difficult to tell the precise age of oaks that grow in fire-prone areas.  Like many local oaks, Quercus berberidifolia re-sprouts after a fire. So the age of individual stems may be significantly less than the actual age of the plant.  For more on the fire-relations of this species, see reference 10.

California scrub oak (Quercus berberidifolia): foliage

Quercus berberidifolia has small, often holly-like leaves – hence the scientific name.  The leaves are thick, stiff and shiny to dull above.  The undersides of the leaves have sparse hairs (trichomes).  The shape of leaves can vary tremendously, even on a single plant (see references 9 and 11 for examples).

Like all oaks, Quercus berberidifolia is wind pollinated.  The separate male and female flowers occur on the same tree.  Plants bloom in winter or early spring – usually February or March at lower elevations.  The male flowers, with their yellow pollen, grow on dangling, one-inch catkins. The pollen is not usually a problem for human allergy sufferers. The female flowers are often hidden by leaves.   The acorns, which develop from the female flowers, are broad and chunky.  They look distinctively different from the longer, tapered acorns of the Coast live oak (Quercus agrifolia) and Quercus dumosa. Acorns ripen 6-8 months after pollination.  New seedlings can be started quite easily from fresh acorns in the fall.

California scrub oak (Quercus berberidifolia): sunny site

California scrub oak likes a site with full sun to part-shade.  It grows in most well-drained local soils except those with high salinity (no recycled water).  It can succeed in clays and clay-loams, as long as summer water is kept to a minimum.  In soils with reasonable drainage, it can be deeply watered every 4-6 weeks during the dry season.  The first 4-5 years, when plants are establishing, they require monthly water in most locales. Then plants are quite drought tolerant.  This species has deep roots that require a few years to develop. 

It’s best to let oak trees self-mulch, and Quercus berberidifolia is no exception. Oak leaves help with soil moisture retention.  They also contain plant chemicals that likely provide protection from pests and diseases. The leaves also repel slugs, snails and grubs.  So, leave the leaves in place when they fall.

California scrub oak is generally easy to grow. It is susceptible to several oak pests, including several types of borers, and to soil and other fungal diseases.  For an excellent guide to the pests and diseases of California oaks see reference 12.

Scrub jays and others love acorns!

The California scrub oak is an excellent habitat plant.  The dense foliage provides cover and nesting sites for birds. The shade and cover are utilized by smaller, ground dwelling animals from rabbits to lizards and doves.  The acorns are a favorite food of Jays, woodpeckers, squirrels and other animals.  In the wilds, young foliage is sometimes browsed by larger animals (deer, sheep, bears).

Oaks in general provide important habitat for a wide range of beneficial insects. These, in turn, attract the insect-eating birds.  Butterflies for which this oak provides larval food include the California Sister, Propertius Duskywing, Mournful Duskywing, Golden Hairstreak, and Gold-Hunter's Hairstreak.

California scrub oak (Quercus berberidifolia): habitat
 for Duskywing butterflies

The acorns of Quercus berberidifolia are edible, though not as tasty as those of other native oaks, particularly the Black oaks.  Acorns must be leached of their bitter tannins – an involved process – before being useful as acorn meal.  The galls that grow on oak trees are strongly astringent and were traditionally used in the treatment of bleeding and chronic diarrhea. 

California scrub oak (Quercus berberidifolia)

In summary, native scrub oaks can be useful evergreen shrubs or small trees in suburban landscapes.  They can be used as background shrubs, for large hedges/hedgerows or pruned up as small shade trees.  They grow well on slopes, with a minimum of care once established.   They can be planted in dry parking strips and can even be used as bonsai or container plants.  They can be shaped or left to develop their own natural form.  They are resilient and water-wise.

Oaks also have much to recommend them as representatives of our California heritage. They bring many types of wildlife to the garden and even provide a source of human food. They recall a time when oaks were key to human survival.  They are among our most important native plants and their habitat is disappearing in some areas.  That’s why Los Angeles County oaks are protected by The Los Angeles County Oak Tree Ordinance.  And these are just a few reasons to plant Quercus berberidifolia in your own garden.

California scrub oak (Quercus berberidifolia): part of mixed hedgerow,
 Mother Nature's Garden of Health

For plant information sheets on other native plants see: http://nativeplantscsudh.blogspot.com/p/gallery-of-native-plants_17.html


  1. http://tchester.org/plants/analysis/quercus/scrub_oaks.html
  2. https://www.researchgate.net/figure/Distribution-of-nine-White-Oak-species-in-California-a-Quercus-berberidifolia-b_fig1_308632217
  3. https://www2.palomar.edu/users/warmstrong/hybrids2.htm
  4. http://sandiego.sierraclub.org/rareplants/203.html
  5. http://danr.ucop.edu/ihrmp/proceed/nixon.pdf
  6. http://www.biosbcc.net/b100plant/htm/qberberidifolia.htm
  7. http://plantid.net/Gallery.aspx?Taxon=Quercus%20berberidifolia
  8. https://calphotos.berkeley.edu/cgi/img_query?where-genre=Plant&where-taxon=Quercus+berberidifolia
  9. http://nathistoc.bio.uci.edu/plants/Fagaceae/Quercus%20berberidifolia.htm
  10. https://www.fs.fed.us/database/feis/plants/shrub/quespp2/all.html
  11. https://www.smmflowers.org/mobile/species/Quercus_berberidifolia.htm
  12. http://www.suddenoakdeath.org/pdf/psw_gtr197.pdf

We welcome your comments (below).  You can also send your questions to: mothernaturesbackyard10@gmail.com


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