Pacific Northwest Native Plant Profile: Oregon grape (Mahonia species)

Mahonia aquifolium (landscape)

Oregon grape plants are colorful western shrubs with year round appeal and chances are there’s a species that will fit into your Pacific Northwest landscape. Named after Bernard McMahon, an Irish-born American nurseryman, the genus Mahonia is a member of the barberry family (Berberidaceae). But you may also see Oregon grape classified as Berberis, indicative of the extensive debate among botanists on how to classify this species. Although included in the large genus Berberis (an alteration of the Medieval Latin barberis, or barberry, from Arabic barbārīs), Oregon grape is still known as Mahonia in most commercial horticulture, so either is correct (at least as far as I’m concerned!). 

Wildlife value
Like all native plants grown where they evolved, Oregon grape plants are extremely beneficial and attractive to wildlife. Flowers provide for pollinators like bees, moths, butterflies, and hummingbirds, while the fruits, which may remain on the plant into winter, are favorites among birds such as towhees, robins, and waxwings, as well as mammals. Some butterfly and moth species rely on Oregon grape plants to host their larvae, including the brown elfin butterfly. Year round cover may support arthropods, birds, reptiles, amphibians and small mammals.

Cedar waxwings feed on Cascade Oregon grape (M. nervosa). ©Eileen M Stark


Three species
You can’t go wrong with tall Oregon grape (Mahonia aquifolium) for an evergreen, erosion-controlling, woody-stemmed, slightly prickly screen, barrier or woodland border, as part of an unpruned hedgerow, or as an accent plant (pictured top). Aquifolium means “water leaf,” likely named after the lustrous, wet-looking surface of the plant’s leathery leaves that Lewis and Clark first noticed near the Columbia River. Introduced to Britain in the 1820s as an expensive ornamental, its holly-like, pinnately compound leaves begin a bronzy coppery color, then mature to a deep green, with orange, red, or purple highlights in very sunny or cold conditions. Dense clusters of showy golden-yellow, lightly fragrant flowers appear in early to late spring. Ripening in late summer, the dusty-blue, round to oblong berries are slightly reminiscent of grapes, hence the name. Although they are tart and have large seeds, they are suitable for jams and jellies (with beaucoup sweetener) and have traditional medicinal properties, as do the roots. 

Tall Oregon grape’s range includes most of western Washington and Oregon, parts of Idaho and much of California, as well as northeastern Washington and southern B.C. It can handle nearly full sun to shade, but being a woodland species often found growing in somewhat open forests, it prefers some shade (although very deep shade will result in fewer flowers and fruit). Though it does best in slightly moist, acidic, well-drained soil, it’s an undemanding plant that can handle many soil types and drought when established. However, it is intolerant of poorly drained soils and high water tables. Since it will gradually spread into a thicket via tough rhizomes, place it away from pathways and allow it to eventually spread into a wildlife protective clump. If you don’t plan for its growth or it somehow gets out of hand, roots may be occasionally pruned and stems may be cut (as seldom as possible) nearly to the base for renewal. Arching stems typically reach four to eight feet in height, sometimes on the lower end in garden situations.

Try growing it with trees and shrubs such as Douglas-fir, western hemlock, ponderosa pine, vine maple, Indian plum, oceanspray, serviceberry, salal, and smaller companions like sword fern, western columbine, fleabane, delphinium, and others.    

Cascade (or long leaved) Oregon grape (Mahonia nervosa) is another handsome plant, but this one grows only up to about three feet tall,Mahonia nervosa often lacks shiny leaves, and very slowly spreads into a lovely, evergreen, soil-stabilizing ground cover over many years. Nervosa means “having distinct veins or nerves” and refers to the leaf venation. Showy, fragrant, erect, pale to bright yellow flowering stalks, which put on their show in early to mid spring, are trailed by the familiar deep blue berries in late summer to fall. 

This species naturally occurs in moist to dry forests, at low to mid elevations mainly west of the Cascades including Vancouver Island, often with oceanspray, osoberry, vine maple, sword fern, salal, and oxalis, but it’s also an associate of the drier Oregon white oak and madrone habitats. It prefers shade to part shade in moist, acidic soil, but can handle drought in cool areas when established. It’s a nice substitute for invasive English ivy.

Low (or creeping) Oregon grape (Mahonia repens) is an evergreen ground cover that grows one to two feet tall and four to six feet wide. It has a large range in the west; in Washington and Oregon it is mainly found east of the Cascades growing in conifer forests, so it does well in dry, shady conditions but can take some sun. Its leaves (pictured below) may be glossy or dull, tend to be rounder and—though toothed—feel less prickly than tall Oregon grape. In nature, where its range sometimes overlaps with tall Oregon grape (and in garden situations where we often place plants that Mahonia repensdon’t belong together), it may hybridize with its cousin and produce plants that are a bit taller than the true species. 

 

 

 

 

 

 

Propagation 
All Oregon grape species are best grown from seed (without drying them), with at least three months of cold stratification outdoors (wet, pre-chilled seed may also be planted in spring). Seed germination is reportedly erratic and unpredictable. If you have established plants you may find their progeny beneath them or elsewhere, as seeds are dispersed by birds and mammals; anything but very small transplants may not survive. Cuttings may also be tried in late fall. 

As always, buy plants propagated from source material that originated as close as possible to your site. Using such “local genotypes” helps ensure that you get plants that are well adapted to your area and that genetic diversity—which helps plants (and animals) adapt to changing conditions—is preserved. Ask growers and nurseries about their sources if you’re unsure.

Do you have Oregon grape but aren’t sure which species you have? This page has a handy leaf comparison (see photo on lower right column).
 
 
© 2019 Eileen M. Stark

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Best Early Spring-Flowering Shrubs for Pacific Northwest Pollinators

Ribes sanguineum

Plan ahead for hungry native pollinators who need early-flowering plants like red-flowering currant to survive.

 

April showers may bring May flowers, but what about providing forage for hungry pollinators that need food earlier in the year? To provide large amounts of nectar and pollen in late winter and early spring for emerging bees as well as hummingbirds and other pollinators, to help you endure the gray winter skies and store carbon, and to get the most bang from your buck, add early-flowering native shrubs to your garden. Get new shrubs in the ground preferably in autumn—so the plants benefit from winter rains, and to ensure that you have the early part of a continuous succession of flowers covered.

Here are five early-flowering shrubs (plus one shrubby tree that’s pollinated by wind), listed in order of size from largest to smallest, that naturally occur in large areas of the Pacific Northwest region west of the Cascades. They grow in sun to partial shade, are fairly easy to find at native plant nurseries (as well as nurseries that don’t focus on natives), and are quite easy to grow, provided they are kept adequately moist until they are established (2 to 5 years). All would do well planted in wide, unpruned hedgerows. When choosing any shrub, note its eventual width to be sure you have enough space for it to stretch its limbs and attain its natural form at maturity—and to eliminate future hack jobs by a pruner. 

Buy plants that are responsibly propagated from source material that originated as close as possible to your site. Using such “local genotypes” helps ensure that you get plants that are well adapted to your area and that genetic diversity—which helps plants (and animals) adapt to changing conditions—is preserved. Ask growers and nurseries about their sources.

Salix scoulerianaScouler’s willow (Salix scouleriana): A fast-growing deciduous shrub or small tree. Flowers are soft catkins, larger than horticultural “pussy willows,” and appear in early to mid-spring. Male and female flowers are on different plants, so grow both for seeds. Scouler willow is a larval host plant for several butterfly species. Does not tolerate full shade. Prefers moist soil. 20-30 feet tall by 10-15 feet wide at maturity. 

 

Oemleria cerasiformis

 

Osoberry (Oemleria cerasiformis): A large, arching deciduous shrub or small tree that blooms prolifically in late winter as leaves emerge. Tolerates clay soil well, but does best with some shade (nature places it in the dappled shade of tall trees). Plants are either male or female, so plant several to produce the fruit that birds need. 12-18 feet by 10-14 feet at maturity.

Amelanchier alnifolia

 

 

Serviceberry (Amelanchier alnifolia): A versatile, multibranched shrub with lovely white, fragrant flowers in mid to late spring. Bluish-green leaves turn gold to reddish in autumn. Larval host plant for several butterfly species. Needs well-drained soil with adequate organic matter. Tolerates full sun in cool areas. Doesn’t like competition, so plant other shrubs and perennials at least several feet away. 8-18 feet tall by 6-10 feet wide at maturity.


Red-flowering currant (Ribes sanguineum)
: An upright, deciduous shrub with nearly year-round appeal. Gorgeous, pendulous, lightly fragrant flower clusters (pictured, top) that bloom in early spring are followed by powder-blue berries. Leaves turn golden in late autumn. Larval host plant for butterfly larvae. Controls erosion. Can’t handle excessively wet soils, so be sure soil drains well and plant it away from rain gardens and other drainage areas.  7-10 feet tall by 6-9 feet wide at maturity. More info in this post


Mahonia aquifoliumTall Oregon grape (Mahonia aquifolium)
: A handsome, multitalented evergreen shrub with an upright growth habit. Bursts into flower brilliantly in early to mid-spring, for a long period. Tolerates acidic soils. Has somewhat prickly evergreen leaves, so site it where it won’t be brushed against frequently. 5-9 feet tall by 3-6 feet wide. Will spread slowly. More info in this post.

 

The earliest winter bloomer is the handsome beaked hazelnut (Corylus cornuta var. californica), a beautifully textured, large multistemmed woodland shrub or small tree that grows to 10-20 feet tall by 10-20 feet wide. It is pollinated by wind, not animals. More info here.

After planting
Add a few inches of organic matter as mulch around the shrub (but keep away from trunk) to insulate, keep weeds down, and add nutrients. Fallen leaves work well, as does weed-free compost. If you use wood chips, make sure they aren’t finely ground and/or fresh, and don’t dig them into soil—under-composted chips and bark can deplete soil of nitrogen during breakdown. Later on, simply allow fallen leaves to remain on soil to provide habitat and nutrients.

All of these shrubs are drought tolerant when established (although Scouler willow does best with supplemental summer water), but they will appreciate some irrigation in very hot situations. They should need little to no pruning if they’ve been sited to allow room for their growth.

If you already grow any of these shrubs, I’d love to hear what wild species you’ve seen attracted to them. Or how much they brighten your garden on drab winter days?


© 2015 Eileen M. Stark

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