What happened to my azaleas?

Published 4:21 pm Friday, April 14, 2023

Getting your Trinity Audio player ready...

I get these calls from time to time and there are several answers to the question, “What happened to my azaleas.” This is one that takes a few more questions to get to the bottom of the problem.

First, I ask, “What are they doing?” The first caller has one azalea out of several that has bloomed but turned brown. There are a few things that can cause this, the first of which is frost. Some azaleas put on new growth before they bloom. This new growth is not going to be hardened off to the cold at all. When it got cold a few weeks ago, this bush was probably further along than the others or maybe not in a protected area. I have seen this happen in my landscape this season. Another possibility can be the azalea lace bug. I have done past articles on this pest. The leaves begin to have a dull, stippled look on the upper surface and black spots on the underside. These are symptoms of the azalea lace bug. Lastly, there could be a root-rot issue that has killed the plant but there was enough energy left for one last hoorah. In this case, we can dig it up and check the roots. Often, they will be rotten and emit a rotten odor. There are tests that can confirm the root rot but even if confirmed, there isn’t a treatment available that will bring the plant back to life.

While it isn’t possible to prevent these things from happening, maintaining a healthy azalea is the best way to minimize damage from pests, disease, and even environmental issues such as frost. Azaleas like a lower pH so make sure to have the soil tested every two to three years. Use acidic fertilizer such as ammonium sulfate (21-0-0) for your nitrogen needs if recommended on the soil test. Fertilize azaleas after the spring bloom and not before the last frost. This can minimize damage to shrub from frost. Make sure not to fertilize after August, this could delay dormancy and cause brown leaves to be there all winter.

The second question is, “Why have my azaleas bloomed at the bottom and not the top of the plant?” This is a great question and opens us up to either operator error or environmental conditions. Any plant that blooms before Memorial Day is most likely blooming on last year’s wood. This means that those flower buds take an entire season to develop. If a plant is blooming after Memorial Day, then it is most likely new wood. This means that the blooms form on this season’s new growth. This is important because when you prune may have quite a bit to do with whether or not you have blooms this season. In the case of azaleas, they are mostly spring bloomers on old wood, so they should be pruned for shaping and air-flow right after the blooms drop. If pruned in the fall or winter, you probably pruned this season’s blooms right off. Some azaleas are season long bloomers. In this case it is still best to prune prior to June 1st or right after the spring bloom is finished. Shaping can be done throughout the summer but this only removes the longer new growth, not the entire outer edge of the shrub.

The second issue here could be that cold snap and frost we got in early March. Being a warm January and February, most lants were ahead of schedule. Many of our azaleas were just before blooming when that frost occurred. I have probably close to 25 azaleas around my house and I watched to see when the blooms were going to come out. I have several, that are in direct sun all day, which were days from blooming when that cold snap came. Being in an exposed location, these bushes were really ahead of schedule and had the same issue with the tops not blooming but the bottoms did. I had others that were also close to blooming but located under trees which bloomed just fine. The bloom is staggered with some early bloomers and some later. The later bloomers still had tight buds when the frost occurred, they turned out just fine. So, this has to do with location and cultivar or variety as well.

Where plants are located has so much to do with their health and bloom.  Southern exposure allows the plants to receive the most sun all day but also makes them vulnerable to the first rays of sun on cold mornings. This is when the most damage can occur. If there is frost on the plant the cells are frozen too. As the sun warms the tissue, the cells will burst if warmed too quickly. This can happen this time of year on young fruit trees or any young smooth-barked tree. I have camellias on the eastern side of my home and directly beside the house on the southern side. I lose the blooms on the eastern side to frost much quicker because they are more protected from the sun until the frost is able to melt. Of course, we always want to go back to the Right Plant, in the Right Place.

If you are having trouble with growing in your home landscape, call the Extension office at (252)946-0111 or email me at gene_fox@ncsu.edu. Happy Gardening!