What’s causing black crust on azaleas? Let’s solve that mystery

Credit: Allen Sheneman

Credit: Allen Sheneman

Q: I have no idea what is affecting my azaleas. The stems are covered by a black lumpy crust, and all the leaves except the ones at the ends of the stems are black. Allen Sheneman, email

A: When lower leaves on a shrub all turn black, I immediately think of sucking insects that might cause this, like thrips, spider mites, mealy bugs, aphids, scale and whiteflies. The first two are tiny and can’t do what you’ve described. But the other four can. Based on my experience, the black stems and leaves are caused by a bad infestation of whiteflies and scale insects. Both creatures are famous for sucking more sap from a plant than they can digest. They excrete the excess as a sticky liquid called honeydew. The honeydew coats everything, and a sooty mold grows on it to make things black. Check my website for tips on how to control the insects.

Q: We continue to have the same problem with our Limelight hydrangeas. During bloom, we always get the flowers hanging down to the ground. Anything we can do to prevent this? Freddie Lovett, email

A: Even a good thing can be improved. The Limelight hydrangea was patented in 2002 and was a sensation in the garden world. The big flowers are a pretty pale green in midsummer, fading to shades of pink and purple by fall. There’s nothing like it in the landscape. But one of the weaknesses of Limelight is that it flops: Stems are sometimes too thin to hold the flowers up high, as you have found. Careful winter pruning can fix the problem, but it’s a pain to do it every year. So Limelight Prime was introduced in 2021. Not only do the green flowers fade to prettier colors, but the stems are thicker, leading to a plant whose flowers don’t flop. So you have two choices: replace your Limelights with Limelight Prime, or learn how to prune them correctly. I have notes on how to do so at bit.ly/GAlimeprune.

Q: My wife and I planted coneflowers in pots to encircle our pool for a wedding. I have always planted perennials in the ground to ensure their winter protection. Can I expect coneflowers to survive over the winter in pots? Pete Dawkins, Dunwoody

A: My bet is on the coneflowers. They’re tough and winter-hardy down to minus 30 degrees after dying back to the roots in the fall. Of course, the pots will be ugly then, so once you remove those brown stems, plant some annuals like ornamental cabbage, chard and pansies to make spots of color around your pool.

Email Walter at georgiagardener@yahoo.com. Listen to his occasional garden comments on “Green and Growing with Ashley Frasca” Saturday mornings on 95.5 WSB. Visit his website, www.walterreeves.com, or join his Facebook page at bit.ly/georgiagardener for his latest tips.