Blooming in spring through mid-summer, Rhododendron offers delightful blooms in vibrant colors or soft pastels for gardens in zones 4-9. This woody shrub, a relative of the Azalea, pushes out trusses of bell-shaped flowers with visible stamens that brighten partially shaded areas of the garden. This shrub is an evergreen perennial that offers year-round interest even long after the blooms fade. 

A Staple Perennial to Build the Garden Around

Rhododendron prefers a moist, cool climate which makes it an excellent choice for Pacific Northwest gardens. With a shallow root system, this perennial is best planted in the spring in cooler climates and planted in the fall in warmer climates. This allows the plant plenty of time to establish without the shock of severe heat or cold. With over 1,000 varieties, Rhododendron can grow anywhere from 2-8’ tall, so pay attention to growth habits and not just color when choosing your new plants.

Planting and Care

When planting Rhododendron, choose a location that is partial to full shade so the plant isn’t scorched by the sun. Water the shrub thoroughly prior to planting. Dig a hole slightly wider than the nursery pot, loosen the roots of the plant, and insert it into the hole ensuring that the root ball is several inches above the soil. Pack in the soil to help the plant sit upright. If adding mulch, make sure that it is several inches away from the main stem or trunk of the plant.  

The shallow root system of this plant means that it will show physical signs of wilt and distress when it is lacking water. Consistent watering is key to helping Rhododendrons thrive. Pay extra attention during times of drought.

Rhododendrons bloom on old wood. So prune immediately after they finish blooming, taking care not to prune off next year’s growth. If spent blooms are not removed, the plant will produce fewer blooms the following year. The plant can be pruned into a tree or shapely shrub after the bloom time has ended. If heavy pruning is needed, this should be done in late fall to help shape an overgrown shrub. Note that a heavy pruning will result in little to no blooms for the next 2-3 years, but is well worth it for the health of the plant.

Fertilizing Rhododendrons in the fall is helpful to amend soil. Water the area thoroughly and use a fertilizer specific for acid-loving plants. Water the fertilizer into the soil and keep it moist to avoid burning the roots.

Five favorites for us this season are:  Hotei, Mrs. Betty Robertson, P.J.M., Tortoiseshell Wonder, and Yaku Prince.