Rhododendrons are a favorite flowering plant in gardens across the United States, particularly in cool and moist environments like the Pacific Northwest. Nearly 1,000 species occur within the genus Rhododendron, including a variety of shrubs and small trees prized for their showy blooms and attractive foliage. Despite the great variety of plants within the genus, most rhododendron species require the same basic cultural and care requirements, including abundant water, humus-rich soil and bright, indirect sunlight.
Locate the plants in a site that offers protection from the wind and afternoon sun. Avoid planting rhododendrons in areas where water pools, since this will negatively impact the roots.
Test the soil acidity before planting rhododendrons. Amend the soil with elemental sulfur if the pH reads 5.6 or higher; rhododendrons require moderately acidic soil to prosper.
Cultivate the rhododendron bed with a rotary tiller until the soil is loose, friable and aerated. Spread an 8-inch-thick layer of composted pine needles and oak leaves over the bed. Apply a 1-inch-thick layer of perlite on top of the compost. Cultivate the soil again with the rotary tiller until the compost and perlite are integrated and no large clumps of dirt remain.
Plant the rhododendron so the top of the root ball is flush with the ground or slightly above. Do not plant it too deeply. Remove any burlap sacking or plastic packing from around the root ball before planting it.
Mulch heavily around the base of the rhododendron plant, creating an inwardly sloping ring of mulch so the water is directed toward the base of the plant.
Apply fertilizer specifically formulated for rhododendrons or azaleas only if signs of nutrient deficiencies, such as yellow leaves or stunted growth, are present, or if the plant was grown in an unimproved garden bed.
Water rhododendrons to a depth of 5 inches once a week with supplemental water during times of drought or extreme heat.