Let's Grow: Growing azaleas can be tricky

Azaleas and Rhododendrons are among the most coveted landscape plants. Despite their popularity, few people understand that azaleas belong to the larger Rhododendron family. The Rhododendron family includes almost 1000 different species, including both rhododendrons and azaleas. Most are evergreen but some are not. They are well known for their showy spring flowers and attractive foliage. Generally, azaleas have smaller leaves and flowers than rhododendrons, but they take similar care and growing conditions.

Evergreen azaleas develop as multi-stemmed plants from the ground and usually grow 3-5 feet tall. Because they keep their leaves all year, they aren’t as winter hardy as deciduous azaleas. Cold winters can freeze their flower buds, and foliage may be killed by winter burn. Azalea bloom colors range from white to pink, red, lavender and purple.

Azaleas are highly toxic; their leaves and nectar contain andromedotoxin, a poison chemically similar to turpentine. It is a cardiac poison, first stimulating and then paralyzing the nerve that controls heart function; it also paralyzes the muscular nerve ends. In some parts of Turkey, bees are deliberately fed on Azalea/Rhododendron nectar, producing a mind-altering, potentially medicinal, and occasionally lethal honey known as "mad honey". Azaleas and rhododendrons were once so infamous for their toxicity that to receive a bouquet of their flowers in a black vase was a well-known death threat.

Azaleas and Rhododendrons do well in acidic, organically rich, humusy, moist (not wet) well-drained soils. This means soils that allow excess water to soak in or drain away, but still stay moist. The ideal soil for azaleas is similar that on the forest floor; peat, rotted leaves, pine needles and pine bark. Azaleas planted in clay soil typically dry out and wither away in a few years, because their roots never penetrate into the surrounding soil. Once the food and moisture in the original container mix is depleted, they either starve or dry out, or both. This is just as likely in winter as in summer.

Azaleas are happiest in dappled sun or under the protective shade of trees. Morning sun with afternoon shade can also work. Protection from strong winds helps keep azaleas from drying out or winter burn. Walnut, butternut, pecan and hickory trees secrete juglone, which is poisonous to azaleas, so planting under these trees won’t work. Azaleas and Rhododendrons have shallow, fibrous root systems, so they dry out easily in hot, dry summer weather. Just one dryness event can stunt their growth permanently. Mulching, particularly with pine bark or pine needles, helps.

By now you can probably see why there are so few healthy Azaleas and Rhododendrons in your neighborhood. Creating the specific micro-climate that they need takes a lot of work, and it’s difficult to maintain in areas with heavy clay soils.

We’ve all seen spectacular azalea plantings. There’s nothing quite as impressive when they are in full bloom, but these gardens are rare in southern Ohio. With the possible exception of hybrid tea roses, azaleas have the highest failure rate of any shrub in home landscapes. This is why, unless our customers insist, we try to avoid planting Azaleas or Rhododendrons in our landscape projects.

Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are on the “Garden Advice” page at www.goodseedfarm.com. For more information is available at www.goodseedfarm.com or call GoodSeed Farm Landscapes at (937) 587-7021.

This article originally appeared on Chillicothe Gazette: Let's Grow: Growing azaleas can be tricky