Rhododendron’s are known for their showy blooms and overall aesthetic appearance that compliments most gardens quite well.
So seeing your Rhododendron’s leaves turning black can be quite the cause for concern as this certainly means your plant requires your immediate attention.
There are many causes for black leaves to appear on the plant, so it’s my job to help you find the root cause so you can get your plant back on track to looking it’s best and staying healthy.
So if you have just arrived from google and have this issue, let’s solve it together!
Below are some causes and what you can do about it today.
Overwatering
As you may already know, Rhododendron’s love to be planted in moist, well draining soil, but they don’t like to be sitting in water for too long.
Overwatering is a major cause for Rhododendron leaves turning black and overall root rot.
By overwatering, you end up starving the roots of oxygen and then the plant will struggle to function, producing yellow leaves that eventually turn brown before turning black.
In general it’s always best to stay on the safe side of things and lean more towards underwatering as if that ever causes issues, it’s much easier to fix an underwatered plant than an overwatered one with rot.
Solution
First off to prevent overwatering, you should only water your Rhododendron when the top inch or two of the soil has fully dried up.
Now if you have yellow, brown or black leaves already, you should check the roots for rot.
If they are dark and or mushy then you have root rot and will need to prune away the affected roots and damaged parts of the plant before replanting in fresh soil.
Pests And Sooty Mold
Pests are another annoyance that can affect Rhododendron’s unfortunately.
Pests you may encounter include scales, thrips, aphids and spider mites to name a few.
These bugs will feed on the sap of your plant, causing things like yellow leaves, white leaves, drooping, curling, holes and other issues.
These pests also leave behind a honeydew substance which eventually turns into sooty mold which will turn the area of the leaves black.
Solution
Pests and sooty mold can be dealt with in a variety of ways.
For pests themselves, you may be able to get away with just water and pressure in some cases.
But since you likely have some mold as well, it’s best to use an effective fungicide to take care of this problem correctly.
For this situation, I would use neem oil spray as it’s not only an excellent fungicide but it works great for pests as well.
For the most in depth guide on how to deal with Rhododendron pests, you should check out the article I wrote on how to get rid of bugs on Rhododendrons.
Low Humidity
Another cause for black leaves on a Rhododendron can be attributed to low humidity levels whether grown indoors or outdoors.
Although Rhododendrons are not the type of plants that need high humidity, not having even a small amount can cause the leaves to curl up before turning black and falling off.
Having your Rhododendron grow somewhere between 40% and 50% humidity would be ideal.
Solution
Now of course you can’t control the humidity when growing outdoors, you will just have to live in a suitable area for this to work.
But if you’re growing your Rhododendron indoors, then there are a few things you can do to increase the humidity levels, even just a little bit.
Some of those things include the following.
- Grow near water sources such as kitchens, laundry room, bathrooms, etc.
- Use a water pebble tray underneath or nearby the plant
- Group other plants nearby to share local humidity
- Use a humidifier if you have one on hand
Sun Scorch
Rhododendrons do not tolerate full sun(more than a few hours a day), or intense heat(85 degrees plus) for very long and can get sun scorched leaves as a result.
When your Rhododendron starts to get damaged you may see the leaves turn brown before turning crispy black and then falling off.
You may even see your Rhododendron leaves turning red by the way.
This of course can happen when growing outdoors, but it can also happen indoors if the plant is too close to any given window as the suns rays can get to the plant directly.
Solution
If you’re growing outside, you want to find a spot that gets lot’s of bright indirect light as in plenty of shade.
This can be done under trees, balconies or really anywhere you can find that gets good shade to protect the plant from the hot midday and afternoon sun.
For indoors, you want to find a window that gets lot’s of light, while keeping your plant at least a foot away from any given window to protect it as well.
Low Light
Although intense light or heat can damage the leaves and turn them black, so can really low light conditions.
If your Rhododendron doesn’t receive enough light, you can expect the leaves to curl, turn white before turning brown and then black and eventually fall off.
This usually only happens if you grow the plant in near complete darkness though often when seriously neglecting or forgetting about the plant.
Hopefully this isn’t the case for you.
Solution
As mentioned above, there are a few things you can do to correct a lighting issue.
- Grow under shade to protect the plant
- Grow near windows
- Use an indoor grow light if all else fails
FAQ’s For Black Leaves
Below you will find some FAQ’s on the topic of black leaves on Rhododendron’s.
What Does An Overwatered Rhododendron Look Like?
A few signs that you have overwatered your Rhododendron include droopy or mushy leaves, yellow or brown leaves, black leaves, stunted growth and foul smelling roots. The plant may also look dehydrated if the roots haven’t been able to work properly for some time.
How Do You Treat Black Spots On Rhododendrons?
In the case of black spots on a Rhododendron caused by sooty mold or other fungal issues, you can try using some form of fungicides such as neem oil, copper hydroxide or copper based fungicides in general. Just be sure to keep the Rhododendron in shade until they dry.
Should I Cut Off Black Rhododendron Leaves?
In most cases you should cut off or at least prune back black Rhododendron leaves as they will not likely recover, unless it was just sooty mold causing the discoloration. This makes way for fresh new growth as the plant resources will be better allocated.
How Do You Fix A Rhododendron Leaf Scorch?
Unfortunately, once a Rhododendron leaves have been badly sun scorched or heavily discolored, they won’t be able to return to normal or be fixed. You should instead cut away the damaged leaves so your plant can use more energy towards new growth instead of wasting it on unrecoverable leaves.
Will Rhododendron Leaves Grow Back?
Rhododendron leaves will in fact grow back after some time has passed, assuming there is enough room for new growth and not too many damaged leaves hogging the plants energy. You can expect fresh new leaves around the springtime if everything is right.