“When is the best time to fertilize Rhododendrons?” Question from Carin of Fall Creek, Wisconsin
Answer: When it comes to questions about Rhododendrons and Azaleas, even experts like me turn to the American Rhododendron Society. Their goal is to teach gardeners how to make the most of these beautiful flowering shrubs. Their advice follows that of professional growers: if the plants look happy, perform well, and have fertile, well-drained soil that is slightly acid, then there is no need to feed them. Excess fertilizer can actually damage their roots. But, if your soil is sandy and poor, then I recommend amending it with Black Gold Peat Moss and Garden Compost Blend to increase water- and nutrient-holding ability. From there fertilize in the early spring with a food formulated for acid-loving plants, like rhododendrons. (Click here to read more.)
“I have many azalea bushes in my yard, and this year, I had three suddenly die off. I couldn’t detect any pests or that type of issue. They were around a tree, and all four lost their leaves very quickly. One has sprouted green. One seems quite dead, and the other two are still bendable and not dead, but have no leaves. Any thoughts on what caused this? Also, do you feel the others that are bendable may come back?” Question from Mary of Longwood, Florida
Answer: There are several fungal diseases that can cause stem dieback and/or sudden death in azaleas. All become more pronounced when there is excess moisture, humidity, and the soil is not sharply drained. Here are the top three possibilities.
Azaleas Diseases that Cause Sudden Death
Phytophthora Root Rot (Phytophthora cinnamomi) is a common, fast-acting, deadly disease of azaleas, and excess soil moisture and warmth encourage its growth and spread. Some infected plants will wilt and die very quickly. Others will grow slowly and may have poor-looking living branches, but infected plants typically succumb to death pretty quickly. To identify this disease, look for discolored, reddish-brown roots that are dead or dying. Badly infected plants will show the same discoloration on the lower stems. Remove all infected shrubs and dispose of them away from your garden. Sadly, this disease remains in the soil, so consider raising the soil in your beds to encourage better drainage, and plant something different in the spots. (Click here for good information about the best Florida landscape plants.)
Phytophthora Dieback (Phytophthora cactorum) is the most common azalea disease that causes dieback. It is also a disease caused by poor soil drainage. The first symptom is wilting with leaves that curve inward. One difference from root rot is that the roots look blackened and pull up easily. The stem will often show brown discoloration at the base near the soil surface. Treat as you would for Phytophthora root rot.
Rhizoctonia Root Rot (Rhizoctonia solani) is a deadly disease that behaves like the others, but the plants exhibit severe brown and black spots on the leaves, so I don’t think that this is the disease that took your azaleas.
When removing any diseased plant material, rake away and remove any dead leaf or stem material that may be contaminated with disease-causing spores. When pruning your surviving azaleas, avoid cross-contamination by cleaning your pruners in a 10% bleach solution when making cuts from one plant to another. Adding additional topsoil and amending beds and new planting areas with fertile organics, like Black Gold Canadian Sphagnum Peat Moss, will help any future azaleas that you plant.
Azaleas properly planted in well-drained soil need regular water. One other less likely option is that your shrubs dried up due to lack of water. If this could be the cause, I suggest laying drip hose around the remaining azaleas, applying mulch, and irrigating the shrubs once or twice weekly in the absence of drenching rain.
“I am looking for possibilities for flowering accent shrubs (other than roses) for the front of house landscaping. I’d prefer something that blooms throughout the summer if it exists. My Zone is 6a.” Question from Diana of Fort Wayne, Indiana
Answer: There are several flowering shrubs with a long season of bloom that will grow beautifully in your USDA Hardiness Zone 6 climate. Here are four recommendations that are easy and attractive.
Flowering Shrubs for Foundations
1. Smooth Hydrangea varieties (Hydrangea arborescens): Tolerant of sun and shade, smooth hydrangeas are very hardy and native to your region. Some of the new varieties bloom for a long time in summer, and then their blooms remain on the plants and continue to look pretty into fall and winter. I love the many varieties sold by Proven Winners, such as their Invincibelles, among others. (Click here to view them.)
2. Abelia (Abelia hybrids): Abelias bloom and bloom through summer with small flowers of pink or white. Many also have colorful foliage and some are semi-evergreen. Ruby Anniversary is a wonderful compact selection with loads of tiny pink and rose flowers that I have growing in my front yard. Kaleidoscope abelia is another beauty with multicolored leaves and pretty little blooms.
3. Reblooming Yellow Potentilla (Potentilla fruticosaHappy Face®): These mounding 3-foot shrubs bloom all summer with golden yellow flowers. The foliage is very fine and plants are sun-loving.
4. Reblooming Azaleas (Rhododendron spp.): Encore® and Bloom-A-Thon® Azaleas will rebloom and some are even evergreen. I recommend them if you have slightly acid to acid soils with good drainage.
All of these flowering shrubs are tidy and look smart when interplanted with evergreens and perennials. All will become established more quickly with soil amended with Black Gold Garden Compost Blend. I hope that you like these suggestions.
When is an azalea a rhododendron? Always! The American Rhododendron Society website explains: “Rhododendrons and azaleas belong to the genus Rhododendron in the heath family (Ericaceae). Other members of this ornamental-rich family include heaths [Erica spp.] and heathers [Calluna spp.], blueberries [Vaccinium spp.], mountain laurels [Kalmia spp.] and many other important ornamental [and edible] plant genera.