Secrets Of Rhododendron Success

This is the first of 10 stories on least-toxic pest-control strategies to be published before this year's Green Garden tour.

For many gardeners, Northwest landscaping means a swath of lawn and a couple of rhododendrons plopped next to the house foundation. The glories of rhododendrons are spring blooms and strong evergreen leaves, adding a handsome accent to the landscape year-round. But when they are mistreated in gardens, as they often are, rhododendrons become inglorious, lanky messes with ugly problems and little bloom.

To succeed with rhododendrons, first recite the gardener's mantra, "Right plant, right place." Many of the rhododendron growers' common problems are best handled by selecting the right plant, giving it a location it can love, and proper care rather than reaching for some kind of spray. Because so many of you have established rhodies, we'll start with location and care.

Where to plant

The "right place" for rhododendrons is in well-drained soil loaded with organic matter. Think of the springy soil under long-established forest trees. Even big old plants have fine, fibrous roots right at the surface of the soil. Organic matter helps the soil retain water, which rhododendrons like in abundance.

For a new planting of rhododendrons, spade over the entire area and add commercial compost such as Cedar Grove, a commercial sludge such as Groco, or composted steer manure. Amend the entire area, not just the individual planting hole. Rhododendrons like the naturally acid soils of the maritime Pacific Northwest and will appreciate an acid-based fertilizer before bloom. Settle the plant at soil level, no deeper than it was in the nursery container. One "fails to thrive" tip is recognizing "oops; planted too deep."

Sun or shade? Only a few rhododendrons, such as the sturdy PJM, an early-blooming lavender, can take full sun without damage. Many others want filtered light or dappled shade. Too much shade will reduce bloom. And rhodies may not get enough water if they are planted next to big, greedy tree roots. Check with your nursery on exposure needs.

How to water

Wherever rhodies are planted, have soaker hoses handy to give the plants good deep soakings around the entire root area during dry summers. Rhododendrons originated in areas with higher summer rainfall than we get. Be sure to wet all the roots fully; container soils sometimes dry out before the surrounding soil, and your rhodies can suffer from drought even if the area around them seems damp.

A 3-inch mulch of bark, sawdust or compost over the planting bed will also help retain water. (Keep mulch away from the crowns of the plants.) An efficient way to water is to use the "leaky pipe" hoses made of recycled tires. Lay the hoses about 18 inches apart throughout the planting beds.

When new, these hoses like to recoil and bounce up into their own springy shapes. You can control this frustrating tendency by pinning them to the soil surface with the cut-off ends of metal coat hangers. Lay the mulch over the hose. You'll be able to water deeply with little water waste. If your rhododendrons do not get sufficient water in summer, when they are setting next year's flower buds, you'll have a bloomless spring as well as a stressed and unattractive landscape plant. If you do not plan to water, don't fertilize.

Pest resistance

The "right plant" part of the green gardener's mantra means selecting plants with natural pest resistance. You can reduce pesticide use by planting a rhododendron resistant to root weevils, those nocturnal beasties that chew notches in the edges of the leaves. Many lovely species and cultivars have excellent resistance.

Tall-growing resistant varieties include "Point Defiance," a zingy pink and white combination; "Crest," a clear yellow; "Virginia Richards," a salmon-pink and cream vision; and the lavender "PJM." Or you can choose "Oceanlake," a deep blue, or "Dora Amateis," cloud white; these grow low and spreading. Check with your nursery for these and others.

More information

For more information, call 296-3425 and ask for Tape No. 1631, "Growing Azaleas and Rhododendrons." Residents of Seattle, King County and suburban cities in King County can call 547-7561 to get a free map for the July 9-10 garden tour or to receive free educational brochures about least-toxic pest management. To schedule a free speaker and slide show on green gardening for your group or business, call 632-1545.

The Green Gardening Program is presented by Washington State University Cooperative Extension, Seattle Tilth and the Washington Toxics Coalition. It is sponsored by the Seattle Solid Waste Utility and funded by the Local Hazardous Waste Management Plan.

The goals are to create healthier yards and communities, encourage beneficial insects and a balanced ecosystem, protect lakes and streams by minimizing potential chemical runoff and reduce pesticide-disposal costs.

Gardening is published Friday in Scene and Sunday in Home/Real Estate.