It’s normal for some older leaves on Azalea plants to turn red, particularly in the fall. However, if the new growth or all the leaves on your plant are red, it’s a sign that the plant is stressed and struggling, and you should take action to remedy the problem.
Environmental stress is the reason for azalea leaves turning red. This could be down to several factors, most commonly over-exposure to sunlight or overwatering. Azalea can also produce a red pigment called anthocyanin to protect itself from stress factors.
In this article, I’ll take you through some possible reasons why your Azalea might be stressed and give you some pointers on how you can improve the situation.
Causes of Azalea Leaves Turning Red
When a plant gets stressed for any reason, it will often produce anthocyanins in response. Anthocyanins are red or purple pigments that play various roles in protecting the plant from damage. The exact mechanisms of how anthocyanins protect plants are complex and are still being researched. (Source: DePauw University)
Anthocyanins have been shown to protect plants from UV rays in sunlight and increase the effectiveness of photosynthesis in low light levels.
Anthocyanins also play a role in protecting plants from cold temperatures, predators, and highly acidic or alkaline soils.
Try to avoid stressing your plant. Keep it in a stable environment with a temperature that does not regularly exceed 85°F (29°C), away from strong drafts and heat sources.
Ensure that your plant receives plenty of bright, indirect light but limited direct sunlight and keep it in acidic, moist, well-draining soil.
Leaf Spot Diseases
Several fungal and bacterial diseases might cause red, yellow, or brown spots to develop on your plant’s leaves. The spots might combine all these colors, often brown in the center with yellow and red around the edges.
While the organisms that cause these problems are varied, the cause is often bad watering techniques or heavy rain exposure.
When water infected with spores or bacteria splashes onto the leaves of a plant, for example, during heavy rain or when the plant is watered carelessly from above, the organisms can take hold and quickly cause problems for your plant.
The severity of these diseases depends on the organism involved. Red pigmentation is always a sign that your plant is fighting something. If you see brown or yellow spots too, it’s probably a fungal or bacterial leaf spot disease.
Some fungal leaf spot diseases can be treated with fungicides, but others, as well as bacterial leaf spots, are almost impossible to treat once they’ve taken hold. It is always better to prevent these diseases than try to cure them.
The best way to avoid disease in your Azaleas is to remove fallen leaves and debris from your plant’s pot, as spores and bacteria live here – waiting for the chance to splash onto your plant.
Always be careful not to get water onto the plant’s leaves and stem. Protect it during heavy rain and, ideally, water the plant from below. This not only minimizes the risk of infection but increases the strength of the plant’s roots.
Azaleas are not heavy feeders, but they do need a range of nutrients, including phosphorous, nitrogen, magnesium, and iron, to be healthy.
If levels of these nutrients are too low, the plant will display various symptoms such as slow or stunted growth that may be pale, yellow, red, or very dark green.
An important thing to remember when growing Azaleas is that they need acidic soil to absorb nutrients effectively.
If the leaves on your Azalea are turning red around the edges or in blotches, the problem could be one of the following nutrient deficiencies:
|Nitrogen||Pale, stunted new growth with red edges and/or blotches on older leaves.|
|Phosphorus||Unusually dark green leaves, developing into dark red blotches or stripes along the midrib.|
|Iron||Yellowing of young leaves between veins, with veins themselves remaining green. Leaves may turn red at the edges or in splotches. Older leaves are the last to be affected.|
|Magnesium||Leaves turn yellow from the tips, including the veins. Reddish-purple blotches may develop on the upper surfaces of leaves.|
|Manganese||Similar symptoms to iron deficiency, though less severe.|
Most nutrient deficiencies are easy to solve by giving the plant more of the relevant nutrient. It can be difficult to determine which nutrient your plant is missing, though. One option is to get your soil lab-tested, which will give you a breakdown of the nutrients in the soil.
If you choose this route, it’s important to remember that Azaleas need acidic soil to access the nutrients – the soil could be full of nutrition, but if it’s too alkaline, the plant won’t be able to absorb it properly.
As Azaleas like acidic soil between pH 4.5 – 5.5, it’s best to use a potting mix specially developed for acid-loving plants.
This will ensure that your plant can absorb the nutrients that it needs, and you shouldn’t need to do much other than giving it a feed once a year in spring, again with a fertilizer developed for acid-lovers.
Always follow the instructions, and don’t be tempted to over-feed your plant, as this can burn the plant’s roots and cause more problems.
If your plant is potted in general-purpose compost or alkaline soil, you’ll probably need to acidify it. You can use a light application of ferrous sulfate to lower the pH. Never use aluminum sulfate as it is toxic to Azaleas.
Too Much Sun
Azaleas are happiest in a position with dappled light and shade, where they don’t get too much direct sunlight on their leaves.
When too much strong sunlight falls on a plant’s leaves, it impairs the function of the leaf, and the cells begin to collapse, causing the leaves to curl and eventually drop off the plant.
If the sun damage isn’t too bad, for example, if the plant is getting burned for an hour a day over a long period of time, you might get some warning that there’s a problem – the leaves will turn dark red before drying out and becoming brown.
The plant produces anthocyanins which protect the leaves from the harmful UV rays in sunlight – giving them a red appearance.
However, if the sun damage is very acute, for example, several days of the hot, direct summer sun, the plant might not survive – it doesn’t have time to produce its natural anthocyanin sunscreen, and its leaves will quickly scorch – become dry and brown before falling from the plant.
Keep your Azalea in a position that receives plenty of bright but indirect light, with at most a couple of hours a day of direct sunlight on the leaves.
Never keep your plant on a windowsill or very close to a window, as it will be prone to sun scorch – the glass of a window intensifies the sun’s rays meaning they will very quickly burn your plant.
If you keep your plant in a position where it gets some direct sunlight, make sure that it is several feet from the window.
Lack of Light
Although they enjoy a fairly shady position, Azaleas don’t do well in deep shade. When they don’t receive enough light, they produce Anthocyanins which help the plant increase the effectiveness of photosynthesis. You might notice leaves which turn deep red and lean towards the nearest light source.
Make sure that your Azalea gets at least 8-10 hours a day of bright, indirect light. If you notice your plant leaning towards the light or its leaves becoming darker green to red, move it to a position with more light.
Under or overwatering
Azaleas like consistently moist, well-draining soil. If the soil is too wet or too dry, the plant will become stressed, and the leaves will redden due to the production of anthocyanins.
In either case, the plant will display symptoms of dehydration – limp, curling leaves which gradually die off. If you notice these signs, don’t automatically water your plant – if it’s already waterlogged, you’ll make the problem worse!
A waterlogged plant can become dehydrated because when its roots are surrounded by water, it can’t absorb anything – including water.
Water your Azalea when the top couple of inches of compost are completely dry. Always check first using your finger or a moisture meter, and never give your plant water if it doesn’t need it. Never water to a schedule as a plant’s requirements vary depending on the season and situation.
Should You Worry About Azalea Turning Red?
In short, it depends. If a few of your plant’s older leaves turn red before dropping off the plant, this is perfectly normal. However, if your plant’s new growth is red, or all the leaves on the plant are turning red, it’s a sign that something needs to change in your plant’s environment or the way you are caring for it.