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Over the years, I have been asked many times about rhododendrons where the leaves have turned brown and sometimes the leaves also appear to be drooping which is covered in a separate guide. Most of the time, having brown leaves on your rhododendron is usually the result of something known as leaf scorch and sometimes even powdery mildew.
Leaf scorch is usually caused by very cold weather, especially wet weather where the soil is saturated but also by the complete opposite, heat stress. I would say, most of the time it’s simply the weather which I why it usually happens in winter but it’s usually not noticed until spring when people tend to get out into their gardens.
You can do something about each of these issues to help your plant so read on to learn more about the causes and possible ways to help your rhododendron recover.
If your rhododendron’s leaves look like they are scorched or burned, leaf scorch is most likely the issue. This is especially so if the leaves themselves are crisp and drooping downwards. The good news is that this isn’t a disease but a result of stress caused by environmental factors. And it’s usually something that you can easily put right. In fact, usually, it will actually sort itself out and recover in spring as new leaves spear.
Cold freezing temperatures
Rhododendrons caused by leaf scorch caused by cold winter weather will likely recover on their own. Rhododendrons grown in pots can be brought into a sheltered position or a cold greenhouse to give them a little more protection over winter. You can also wrap them in fleece when very cold weather is forcasted.
Water – too much or too little
Water may be causing the stress– either by an excess of watering or by drought. Check to see if the soil around the rhododendron is water-logged and pooling water, or if it’s very dry due to a lack of rain or watering by you. During periods of drought, water regularly to keep them hydrated and remember rhododendrons grown on pots need watering much more regularly than those grown in the ground.
The rhododendron may be suffering transplant shock, caused by being moved to a new location. This particularly affects the roots and the stems, but the leaves may also become brown. Give your plant time to recover from the stress of being moved and make sure that it’s in the correct conditions for its best health – partial shade, well-drained nutrient-rich soil and protected from the wind. Also, remember to water newly planted rhododendrons often until they have developed well rooted and established roots again.
If your rhododendron is in a position that gets many hours of direct sunlight, especially in the afternoon, it may be getting too hot. In this case, the burned appearance of the brown rhododendron leaves could be caused by too much sun. Remember, rhododendrons usually grow under trees in shady positions. Rig up a structure that shades your plants during the hottest parts of the day. Even a temporary awning could be enough but it’s best to plant them in a semi shaded position.
What to do in cases of leaf scorch
As well as fixing the specific problem that’s causing the leaf scorch, you can choose to remove the affected leaves from the rhododendron. Give the leaves a chance to bounce back to full health first. If that doesn’t happen, or buds don’t develop, trim the affected leave and branches off the plant. New growth should appear in other parts of the plant from spring onwards.
Powdery mildew is a fungal disease that shows up as a white powder on the flowers, leaves and stems of the rhododendron. In some cases, it can discolour the leaves, turning them yellow, red or brown. Powdery mildew is not often fatal to plants.
What to do
If you have found just a light coating of fine white powder on a few leaves, now is your sign to treat with a fungicide before it spreads.
Overview of pests and diseases
Leaf scorch is not usually caused by any pest but diseases can potentially lead to leaf scorch although its not very common.
Check out my article titled Rhododendron pests and diseases for information about other problems that can arise with your rhododendron.