Grow For It! Rhododendrons in the Gold Country?

By From page B3 | June 25, 2014

“You grow rhododendrons here?”

I smile because, yes, you can grow rhododendrons in Zone 7 Mediterranean climate — with some research on varieties, preparation of a planting space, some nurturing and patience.

Like some “gentler clime” gardeners, I came to the Georgetown Divide (rocky, sun-drenched clay at 2,200 foot elevation) determined to create a cottage garden.

Twenty-six years later, that dream has morphed into a lush rhododendron garden outside my house’s eastern “L.”

While having the cottage garden feel, mine features less-thirsty, clustered perennials in a shady habitat, providing visual beauty and respite from the summer heat, with rhododendrons as the backdrop.

First do research: rhododendron varieties now span climates from moist fog in the Mendocino Botanical Gardens (Ft. Bragg) to the dry neighborhoods, so first ask your nurseryman for a Zone 7 variety.

The Botanical Gardens’ grower distributes drought-tolerant varieties to local nurseries. I have 2-year-old drought-tolerant types (the jury is still out on those as they won’t bloom until age 5) but, conversely, my happiest success came as a grocery-store gift rhododendron 20 years ago, variety unknown, set too close to the house for its now 6-foot by 4-foot size, but happily thriving.

The rhododendron family (Ericaceae) which includes azaleas, is large. “The Sunset Western Garden Book” (SWGB) notes 800 species and 10,000 named varieties, both evergreen and deciduous shrubs.

My focus has been the evergreen rhododendrons: the large, glossy-leafed shrubs with beautiful January or February blooming “trusses” (the clusters of striking flowers).

After research and purchase, hedge your bets by selecting and preparing a perfect planting ground.

Ideally, rhododendrons like filtered sun beneath tall trees (think “dogwoods” for the right micro-climate). An east- or north-facing, sheltered garden is next-best. Shaded between our house and a red maple slow to leaf out, I’ve provided a supplemental umbrella until June.

Rhododendrons exposed to direct sun will burn badly, with yellow-centered, black-edged leaves — a concern because pruning the burned leaves out has to wait until January/February bloom (that’s a long period of ugly).

The sun’s impact can also change with the season, creating sudden “spotlights” of overhead exposure.

Consider frost exposure also; exposed rhododendrons can be fenced with burlap as a windbreak and mulched heavily. The planting ground should be rich in organic matter, drain well and allow placement of the rhododendron root ball slightly above ground level. In heavy clay soil, consider planting in a raised bed, one to two feet above the original soil level, as suggested in the SWGB.

When I realized my first rhododendron was planted too deeply, it was already giant-sized. I was advised to forklift it out, adding fast draining peat or sand to the soil before replanting — please see caution on root disturbance below.

My compromise was to lower the ground level outside and well beyond the rhododendron’s dripline (the outermost roots), leaving the rhododendron on a large and shallow plateau.

It’s strongly recommended never to cultivate under a rhododendron, otherwise disturb its roots or tamp down the soil because of potential harm to the shallow, spreading roots. Mulch and nurture a rhododendron with pine needles, oak leaves or wood chips to retain moisture. Fertilize before bloom with an acid-plant fertilizer and again throughout the growing season.

I leave a dripping hose on under the plant’s outside edges, one hour a month but I also check the soil often with a moisture meter, the quick, cheap, non-disruptive way to know root-level moisture. The SWGB mentions that rhododendrons “require a constant supply of moisture” — this tool will help you find the balance between over- and under-watering.

Prior to and during bloom, tip-prune young plants to prevent a lanky, sparsely-leaved shape. After established plants have bloomed, cut back to the leaf whorl, which is a cluster of latent buds or a side branch. The bare branch length will sprout new growth to fill in a too-open plant.

Consult American Horticultural Society’s Plant Propagation for ideas of how turn rhododendron prunings into free plants by “semi-ripe nodal cuttings,” simple recycling for those too tender-hearted to throw live growth into compost.

So, you can successfully grow rhododendrons: research less-thirsty varieties, prepare shaded ground, feed, water and mulch patiently, prune bravely. And try not to smile when asked “You grow rhododendrons here?”

There is no public education Master Gardener class Saturday, June 28. UCCE Master Gardeners of El Dorado County are available to answer home gardening questions at local farmers markets and at the office Tuesday through Friday from 9 a.m.-noon by calling 530-21-5512.

Walk-ins are welcome at the office, located at 311 Fair Lane in Placerville.

For more information about the public education classes and activities go to the Master Gardener Website at Sign up to receive the online notices and e-newsletter at You can also find Master Gardener on Facebook.

Susan Corey-Mcalpine

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