Hydrangea leaves suddenly turning purple is a sign of change in the plant’s environment or it signals a fungal disease that’s slowly overtaking your hydrangea shrub.
Regardless of the cause, there are solutions to the problem. There are usually three main causes of purple leaves in hydrangeas and I’m going to cover each. I’ll also offer solutions and preventative tips to prevent future problems.
Causes of Purple Leaves on Hydrangeas
Hydrangea leaves turn purple when there’s a sudden and extreme change in temperature, when there’s a fungal disease, or when the plant is lacking certain nutrients.
Here’s an overview of each:
– Frost Damage
A late frost in spring can cause a purple discoloration of hydrangea leaves. But it doesn’t have to be freezing outside, even cool weather in the fall can cause leaves to turn purple.
This change in temperature can trigger the plan’s dormancy period earlier. Plus, the changes in light condition can inhibit the production of chlorophyll, causing discoloration of the leaves.
You can prevent frost damage by offering your hydrangeas winter protection, although unpredictable weather can still play tricks on your efforts.
Unfortunately, frost can damage newly formed buds as well, so it can interfere with a successful blooming season.
Leaves can also turn black from frost damage and may also fall off as a result.
Of all the reasons why hydrangea leaves can turn purple, frost damage can be difficult to prevent, unless you have a protective cover you can use, or you’ve already been using as a winterization method.
– Fungal Disease
Fungal diseases are relatively common with hydrangea leaves. Purple spots are usually an indication of a fungal disease called cercospora leaf spot.
Because the disease spreads via spores, it’s difficult to keep an ongoing infection under control, so doing all you can to minimize the chances of this disease is you best bet against it.
Cercospora leaf spot starts out usually at the base of the plant, spreading upward the plant if water droplets spread the spores of the fungus to other parts of the plant.
But they can just as easily be spread by winds or by pruning your hydrangeas with pruning shears that haven’t been sterilized correctly.
Apart from the aesthetical downside of cercospora leaf spot, this fungal disease can also have the following effects on hydrangeas:
- Leaves with purple spots can fall off prematurely
- Reduces viable buds
- It can weaken the plant’s natural defenses
Luckily, there are quite a few things you can do to reduce the spread of the disease and even prevent it altogether:
- Always water hydrangeas at the base to prevent splashing the leaves with water
- Clean up debris and fallen leaves that may harbor spores and cause them to spread once water droplets or rain touches them
- Increase air circulation around and in the shrub by pruning tightly packed bushes. Good air circulation will inhibit the germination of spores.
- Treat a severe and widespread cercospora leaf spot disease by spraying the plant with fungicides (try fungicides that contain chlorothalonil, azoxystrobin, mancozeb, thiophanate-methyl or myclobutanil) at 14-day intervals
- Remove affected sections of the plant to stop the spread to other stems or other shrubs
Because fungal diseases can develop resistance to chemical insecticides, it’s best to use preventative methods and even spray hydrangea leaves with organic fungicides such as neem oil at the very first signs of the disease, or even just as a simple precaution.
– Nutrient Deficiency
If none of the above problems apply — that is there was no frost or there are no signs of fungal spot diseases — the fact that leaves on a hydrangea plant turn purple may signal a nutritional deficiency.
Most commonly, it’s a phosphorus deficiency that can cause a purple coloration of the leaves. Phosphorus deficiency can appear as a result of a soil pH disbalance.
A soil pH disbalance is often caused by gardeners wanting to change the color of hydrangea blooms into blue.
To turn hydrangea blooms blue, you need to acidify the soil. There are several soil acidifiers out there, which gardeners can use for this purpose.
However, overdoing the acidification can cause the chemical compounds to bind phosphorus, preventing the plant from absorbing it.
Therefore, if you want to have your hydrangea produce blue bloom, you only need slightly acidic soil, and not an extremely acidic soil environment.
A pH meter can help you make sure you’re not overdoing the acidification and cause your hydrangea leaves to turn purple as a result.
A highly acidic soil can be amended so that the pH balance is restored, but it will take several weeks for the change to show up in your hydrangeas.
You’ll also need to fertilize your hydrangea with a fertilizer high in phosphorus. Make sure to follow dosage recommendations accordingly, so that you don’t end up overfertilizing the plant.
What to Do with Purple Leaves?
Any discoloration of leaves is irreversible. Whether it’s a discoloration caused by sunburn or a lack of nutrients, those leaves will remain discolored until they fall off and new leaves grow in their place.
Regardless of the cause of the event that triggered hydrangea leaves to turn purple, it’s usually best to remove purple leaves, just to prevent any potential fungal leaf problems from spreading.
Removed leaves will eventually grow back into healthy leaves again. If hydrangea leaves keep coming back purple, it means that the problem that triggered it hasn’t been fixed yet (e.g., the soil pH disbalance still persists).
It’s not normal for your hydrangea to have purple leaves. Thankfully, it’s relatively easy to identify the cause of the problem and to take measures to either treat the problem or prevent it in the future.
You can remove hydrangea leaves that are already purple since their color will not change back to green.
Plus, by removing them, you’re also preventing the spread of potential fungal diseases, if those are the cause of the discoloration.
While you can’t do much to prevent frost damage, you can, however, prevent cercospora leaf spot and pH disbalance of the soil.