• Admin

Rhododendron occidentale

Updated: Nov 21, 2021


A native azalea that's deciduous? When we think of rhododendrons, their evergreen boughs with pastel clusters of showy flowers might come to mind. Rarer are the deciduous forms, and our native R. occidentale happens to be one that is also delightfully fragrant. Here again, just as I discussed about other natives such as Acer circinatum replacing Acer palmatum in garden designs, landscape designers have an opportunity to utilize natives in other thematic concepts. Rhododendrons are often used for foundations plantings, woodland gardens, or Japanese gardens, so it stands to reason this Western azalea may be substituted while providing the benefits of natives.


They are quite stunning to come across in their mountainous native habitat. I recall seeing them along a rough road with an adjacent natural spring, above Lake Siskiyou in far Northern California. We may find them locally in the Coast Range as well, and the California Native Plant Society has mapped them east of San Diego, noting their preferred location adjacent to water or within a fog belt. This tells us that they do need regular moisture despite being native to a dry state.


Another benefit is that they should provide some amount of autumn color as the leaves change. Combined with spring bloom and a notable fragrance, R. occidentale provides unique qualities not found with other rhododendrons, or in this case, azaleas. Which leads me to a brief discussion about rhododendrons versus azaleas.


“All azaleas are rhododendrons but not all rhododendrons are azaleas, is frequently referenced from the American Rhododendron Society, but it does not tell us what to look for in their differences. For a best attempt, I turn to Virginia Tech State University Cooperative Extension, Piedmont Master Gardeners for their explanation. They do note that this description is very general, meaning there are always exceptions to the rules.

  • Bloom time — Excluding the repeat-blooming species, azaleas bloom beginning in April whereas rhododendrons usually bloom later in the spring.

  • Flowers — Azaleas have tubular or funnel-shaped flowers. Rhododendron flowers tend to be bell-shaped. Azaleas have one flower per stem but the shrub produces so many stems that the shrub appears covered in blossoms. Rhododendron flowers grow in round clusters at the ends of branches. Both azaleas and rhododendrons have five lobes per flower.

  • Stamens — True rhododendrons have ten or more stamens, which amounts to two per lobe. Azaleas have five stamens, or one per lobe.

  • Color of flowers – Azaleas come in many shades of white, cream, pink, red, lavender, purple, orange and yellow Their color palette is much broader than that of rhododendrons, which tend to be restricted to white, orchid pink, purple, red and occasionally yellow.

  • Foliage – Azalea foliage tends to be elliptical shaped, thin, small and pliable. Most azaleas are deciduous or partly deciduous but many are evergreen, depending on the cultivar and the climate in which the plant is growing. Rhododendron foliage is large, paddle shaped, thick, and evergreen. The underside of the leaves may be scaly and may have small dots.

We have Western azaleas on the West Valley College Campus. At the time when I photographed them in December 2020, they seemed a bit confused; their leaves were still turning but also producing a few blooms. I have not been back since to verify their spring blooms, but I do recall a gentle fragrance. The first two photos below are their campus location adjacent to redwoods, followed by photos from intrepid photographers.


West Valley College Campus Location: Rhododendron occidentale

Library (northeast redwood grove)

Lat: 37°15'52.36"N

Long: 122° 0'27.62"W


Designer's Note: If pink is not your thing, consider another deciduous known as the Exbury hybrids. Their colors are much bolder in yellows, oranges, deep pinks, or white.



From the Jepson Herbarium, this video also introduces two other California native rhododendrons.



 

facts


Botanical Name: Rhododendron occidentale

Rhododendron: Greek, rhodon, for rose, and dendron for tree.

Occidentale: From the West

Common Name: Western azalea

Family Name: Ericaceae


Origin: Native; Coast Range, mountainous and foothill regions into Oregon, the Sierras and east of San Diego, where fog or water is accessible.


design considerations


Positioning: Middle ground, riparian margin, woodland margin

Garden Themes: Native, butterfly, autumn interest, Asian-inspired, shade, riparian, pollinator/butterfly, hummingbird

Uses: Specimen, accent, mass, border, floriculture, informal hedge


identifying characteristics


Type: Deciduous shrub

Form: Upright to round

Texture: Medium

Size: 10' tall and wide (likely smaller in ornamental gardens)


Outstanding Feature(s): Flower, fragrance, autumn color


Stem: Red-brown when young with pubescence becoming gray, smooth and thin bark with age

Leaf:

  • Type: Simple

  • Arrangement: Alternate

  • Shape: Elliptic, ovate to obovate

  • Margin: Entire

  • Color: Light green turning yellow to red in autumn

  • Surface:

Flower: Spring (before leaves emerge). 5-lobed, white with pink and/or yellow blotches (cultivars extend color range). Bell shape

Fruit: Woody capsule


cultural requirements, tolerances & problems


Sunset Zones: 4-7, 14-17, 19-24

USDA Zones: 7-9


Light: Part shade

WUCOLS SF Bay Area Hydro Zone: Moderate

Soil:

  • Texture: Loam with high organic matter

  • Moisture Retention: Persistent moisture

  • pH: Highly acidic to slightly alkaline

Tolerances:

Problems: All parts are toxic; some reports say honey made from rhododendrons can also be toxic.

  • Branch Strength: Not observed at time of posting.

  • Insects: Aphids

  • Disease: Powdery mildew


citations & attributions


Bayton, R. (2019). The Royal Horticultural Society's the Gardener's Botanical: An Encyclopedia of Latin Plant Names. London: Mitchell Beazley.


Calscape. "Western Azalea." California Native Plant Society, Berkeley. Accessed on November 1, 2021, from https://calscape.org/Rhododendron-occidentale-(Western-Azalea)?srchcr=sc57f03eef73109.


Norris Brenzel, K. (Ed.). (2012). The New Sunset Western Garden Book. New York: Time Home Entertainment, Inc.


Pacific Northwest Handbooks. "Azalea (Rhododendron spp.)-Powdery Mildew." Oregon State University, Corvalis. Accessed on November 1, 2021, from https://pnwhandbooks.org/plantdisease/host-disease/azalea-rhododendron-spp-powdery-mildew.


Seiler, J., Jensen, E., Niemiera, A., and Peterson, J. "Western Azalea." Reprinted from Ag. Book 364, Virginia Tech Department of Forest Resources and Environmental Conservation, Blacksberg. Accessed on November 1, 2021, from http://dendro.cnre.vt.edu/DENDROLOGY/syllabus/factsheet.cfm?ID=249.


Water Use Classification of Landscape Species. "WUCOLS IV Plant List." University of California, Division of Agriculture and Natural Resources, Davis. Accessed on October 20, 2021, from https://ucanr.edu/sites/WUCOLS/Download_WUCOLS_IV_List/.


Photos:

9 views0 comments

Recent Posts

See All