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Growing Rhododendron

Growing Rhododendron

Hellikki Rhododendron



Rhododendrons are popular, hardy, early-blooming evergreen shrubs with bell-shaped flowers with 10 stamens. They make good specimen plants, flowering hedges, and massed plantings. Their evergreen leaves also provides winter interest. The varieties we offer are hardy in zones 4 to 7. Rhodendrons require well-drained, acidic to strongly acidic soil conditions, with a pH of 4.5 to 6.0.

Rhododendron can be planted in full sun to part shade locations.

How To Plant

Because rhododendrons require acidic soil, having the soil tested to determine its pH (a measure of how acidic or alkaline a soil is) before planting is recommended. Based on teh soil test, the soil may need to be amended to create a favorable pH range. Soil sulfur is a slow acting, but long lasting option for lowing soil pH. Aluminum sulfate is a fast acting way to lower soil pH. It is applied by thoroughly working a quarter to a half pound into the soil where each rhododendron will be planted.

Plant outdoors in spring after the last frost. After adjusting the soil pH as required, prepare a hole 12 to 18 inches wide and deep, and mix in compost, peat moss, or other organic matter.


To keep soil pH in the optimum range, top dress with 1 cup of soil sulfur and work it into the soil surface every 3 to 4 years. Plants do not tolerate wet soil conditions, so use raised beds and add organic matter in heavy soils to improve drainage. Deadhead faded flowers.

Mulching plants with an inch or two of organic mulch like chopped leaves or straw is beneficial.

Fertilizer Recommendations

Rhododendrons are low to moderate feeders that benefit from regular fertilization. Use low rates of Jack's Classic Acid Special 17-6-6 or another fertilizer formulated for acid-loving plants.

Common Problems

Rhododendrons are usually not troubled by serious problems when grown in a suitable location Aphids, borers, lacebugs, leafhoppers, mealybugs, mites, scale, and whitefly may feed on plants. Diseases including canker, leaf spot, powdery mildew, and rust are occasional problems. Plants are very susceptible to crown and root rot when grown in poorly drained, wet soils.

Treat insect pests with Captain Jack's Deadbug Brew or 70% neem oil. Use Serenade to protect plants from diseases naturally.

Alternative Products

Azalea, hydrangea, and Nanking cherry are other flowering shrubs for acidic soils.

Complimentary Products

Rhododendrons combine well in the landscape with with spring-blooming bulbs and foliage perennials like ferns and hostas.

Product Recommendations

John & Bob's Soil Optimizer can be used as an amendment to improve soil.

Rhododendron Facts

Rhododendron is closely related to azalea. Marjatta hybrid Rhododendrons are cold-hardy, large-flowered varieties bred at the University of Helsinki in Finland.


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