CORVALLIS, Ore. — Rhododendrons and azaleas are Oregon garden icons, bursting into color each spring and brightening landscapes across the state. Spring is also the best time to give these shrubs the care they need to stay healthy, vigorous and beautiful for years to come.
There are several steps gardeners can take now to support long-lived, healthy plants, according to experts with the Oregon State University Extension Service.
Start with a plant health check
Begin with a close look at your plants. Symptoms of nutrient deficiencies often show up in leaf color and size:
- Pale green or dwarfed leaves may signal a nitrogen deficiency.
- Yellow mottling along leaf margins may indicate excess potassium.
- Small, dark green leaves with dead tips can suggest low phosphorus.
- Yellow or yellow-white (chlorotic) leaves can result from too much calcium, often leached from concrete sidewalks or foundations.
Rhododendrons and azaleas prefer acidic soil — ideally with a pH between 4.5 and 6.0 — and when soil becomes too alkaline, nutrients can become unavailable to the plant.
Interpreting leaf damage
Environmental factors can mimic nutrient deficiencies. Leaves may become discolored from sun scorch during hot weather or from frost injury in winter. It’s also normal for interior leaves to yellow and drop off as they’re shaded by new growth — a process called senescence.
Deadhead spent blooms
When flowers fade, remove the spent clusters, or “deadhead,” to help the plant conserve energy and discourage overwintering insects. Snap off the flower heads carefully to avoid damaging new leaf shoots.
If you miss a few, don’t worry — the plants will still thrive.
Pruning and rejuvenation
Rhododendrons and azaleas generally require minimal pruning, but removing dead, diseased or damaged branches keeps plants healthy. For older, leggy shrubs, rejuvenation pruning can restore shape and encourage new growth.
The best time to prune is immediately after flowering, before the plants set buds for the following year. Heavy pruning later in the season may reduce blooms the next spring.
Feeding and soil care
Both rhododendrons and azaleas thrive in slightly acidic, well-drained soils rich in organic matter. Fertilize soon after flowering, using products formulated for acid-loving plants such as rhododendrons, camellias and azaleas.
Organic fertilizers, though costlier, release nutrients slowly and reduce the risk of root burn. Avoid lime and alkaline fertilizers, and do not fertilize after mid-July, as late feeding can stimulate new growth that may not harden off before winter.
Watering and mulching
With their shallow, fibrous root systems, rhododendrons and azaleas require consistent moisture, especially in summer. Water deeply to encourage root growth and ensure plants under eaves or sheltered spots receive water year-round.
Avoid deep hoeing or raking near the base of plants, which can damage roots. Instead, apply a 2- to 3-inch mulch layer of bark dust, sawdust, straw or other organic material to help regulate soil temperature, retain moisture and suppress weeds.
By combining good soil management, timely pruning and regular watering, gardeners can keep rhododendrons and azaleas vibrant year after year — ensuring a spectacular spring show across Oregon landscapes.
Previously titled Give rhododendrons and azaleas an annual check-up each spring
