Rhododendron shrubs produce large clusters of bright flowers, and grow best in regions with cool, wet summers. Mature plants can vary greatly from type to type, with some plants growing to be more than 20 feet tall, and others staying less than two feet. Choose your rhododendron carefully to fit within your garden space so you don't accidentally end up with a gigantic plant in a small garden. Your rhododendron will be the most vulnerable the first summer after planting, but after its roots are established your plant will require very little maintenance.
Add a layer of compost and then a layer of mulch around your rhododendron every spring. Spread compost out to the dripline (area below the widest branches) and cover the soil and compost with two inches of mulch to retain moisture. Compost will add valuable nutrients to your soil, and mulch will keep weeds from growing around your plants. Add to your mulch layer as needed throughout the year to maintain the thick barrier.
Water the rhododendron when the soil feels dry to the touch. Allow the dirt to dry fully between each watering. Leave a lightly running hose next to the main stem for about an hour once a week to water the rhododendron the first season after planting. This technique ensures that water is reaching the root ball, which may not absorb water from the surrounding soil for a few months. When the leaves on your plant are drooping in the mornings, the rhododendron needs to be watered (sometimes leaves will droop on hot afternoons regardless of their water needs, but drooping in the morning indicates dehydration).
Prune away dead or diseased branches whenever necessary. Tip prune your rhododendron (remove the tips of the branches) after the shrub blooms in the spring. Always prune stems at an angle using sharp garden shears.
Watch for signs of nutrient deficiency and insect infestation in your rhododendron. Discoloration of the leaves is a common sign of trouble, and could mean your plant is missing a key nutrient or that a pest has moved in. Orange spotting around the edges of leaves indicates a potassium deficiency, while yellowing in the center of leaves could mean your rhododendron needs magnesium. Yellow, dry leaves could indicate a spider mite infestation, and scalloped, eaten edges around leaves often means root weevils are present. If your plant seems sick and the leaves are discolored or dying, bring a few leaves to your local garden store and ask a specialist to help diagnose your problem.
Wrap rhododendron with burlap bags in the late fall to protect the shrubs from severe winters. Avoid adding nitrogen to your plants after July 15th to encourage winter hardiness. Rhododendron does best with gradual temperature drops, so the plant can become dormant before winter weather hits. However, if the temperatures drop suddenly the plant could be damaged. The insulation provided by the burlap bags will help minimize winter damage.