Yellow leaves on azaleas and other evergreens are no cause for panic

During the past month, I’ve run into many property owners worried that they’re going to lose their azaleas because of recent flushes of yellow leaves.

Some were expecting that the recent warm spell would produce nothing but green leaves, especially on azaleas showing their soon-to-be blooms. But, when one morning they see an inordinate number of yellow leaves, they panic a bit and wonder if they’re going to lose the plants to the big compost bin in the sky.

Let me try to calm some nerves. Remember that the leaves on evergreen plants like azaleas and camellias don’t live forever. Generally, evergreen leaves only last two or three growing seasons. Then, they die and drop.

While some diseases can cause yellowing and mottling of azaleas leaves, I usually point out to my consulting business clients and GardenLine callers that 10-15% of leaves yellowing is perfectly normal. (ABOVE) Plants need energy for new leaves and blooms to come, so it’s just Mother Nature doing her thing.

Consider the two main functions of leaves or needles: to turn sunlight into food, and to store that food. Young, fresh leaves do this quite efficiently. However, older leaves aren’t so good at it anymore. Plus, wind burn, extremely cold temperatures, drought, pests and so on can also cause yellowing leaves here and there. So, the plant decides they're more trouble than they're worth, lets them die, and replaces them with new leaves. Usually, the yellow leaves are on the inside of branches - new leaves at the tips look perfectly healthy.

However, there are two other situations when azaleas can show a higher percentage of yellowing leaves. If they’re yellow with dark green veins, that’s usually a chlorosis problem. (LEFT BELOW) It can be fixed with a feeding or a combination treatment of iron and soil acidifier. Here’s an article that can take you through those steps.

If there are a lot of yellow leaves embedded with “burn spots” and blotching, that could be a disease known as azalea dieback. (RIGHT ABOVE) It can be treated with terrachlor-based fungicides or systemic PPZ- or Banner-based fungicides.

But in the consultations I’ve been doing over the past couple of weeks, 90% of the yellowing leaves I’ve seen are simply the plant doing what it’s supposed to do at this time of year. So, don’t panic. Look to see if the yellowing leaves are limited to 10-15% or less. You also don’t need to worry much about chlorosis because that’s always repairable. And as disturbing as dieback fungal diseases may seem, they’re treatable, too – early on. Don’t wait too long, though, or they’ll be goners.

PHOTOS: Normal Yellowing – The Lawn Forum; Chlorosis – Glendoick Farms; Azalea Dieback – University of Minnesota Extension