Rhododendrons offer the gardener year-round green foliage, bursts of springtime bloom and a range of heights to suit any landscape. The growing region for these exotic-looking shrubbery was once limited to climates with low air humidity (but moist soil), and with cool (yet not brutal) winters. These days, however, much hardier versions exist to enable most gardeners to find a "rhodie" suitable to their climate.
Choose a location that protects the shrubs from high winds and exposes them to a few hours of sunlight a day. Although partial sun is necessary for the rhododendrons to blossom, they also appreciate some shade, especially in warm climates. The shrubs do well against house foundations or under taller trees like dogwood, oak, pine and sweet gum, but not under shallow-rooted or heavily-foliage trees such as ash, elm, beech, birch, maple or poplar.
Rhododendrons thrive in slightly acidic soil. A soil test conducted by your local extension service or through a simple soil test kit will tell you the pH level of the garden area in which you plan to establish your bushes. A pH level of 7.0 is neutral, but rhododendrons prefer a range of 5.0 to 5.5. To lower the pH level, dig in plenty of naturally acidic materials like peat moss, rotted oak leaves or pine needles and let them decompose for several months before planting. Alternatively, add garden sulfur or iron sulfate, following package directions for how much to use per planting hole or square foot.
Soil Texture and Drainage
Rhododendrons crave the rich, moist soil of their native woodland. Add organic material to your soil to improve both sandy, dry soil and clay soil that drains poorly. To improve all problem soil, add 3 to 4 inches of compost, rotted manure or peat moss to the soil and till in to a depth of 8 to 12 inches.
Plant young rhododendrons about two inches higher than they were growing in their pots. Set the plants at least 4 feet apart; it's important to consult the nursery or planting directions to determine the ultimate height and spread of your chosen rhododendron variety. Firm the soil down around the plant roots and water the area deeply.
Maintaining Moist Soil
Once you've planted the rhododendrons, keep their soil consistently moist. In some parts of the country, rainfall during the heaviest growing season---spring and summer---may be enough to meet the shrubs' needs. Check the top inch or two of soil. If it feels dry, give the area around the rhododendron a thorough watering until the soil is damp to a depth of 1 to 2 inches. Train your rhodies' roots to seek moisture by giving them long soaks at infrequent intervals rather than frequent, shallow soaks. To conserve moisture, mulch the shrubs with wood chips, pine needles or shredded leaves. Mulch to a level of 1 to 2 inches for dwarf rhododendrons and up to 6 inches for large varieties.
Feed your rhodies in early spring, when flower buds first emerge, and again in mid or late summer, when the blooms fade and new leaf growth begins. Scratch in several tablespoons (about 1 tablespoon for every foot of height) of 10-8-6 around the outside edge of the bush. Organic alternatives include a shovelful of a mixture of aged manure and the minerals rock phosphate and green-sand.