Hydrangeas are shrubs that grow very pretty flowers with great aesthetic value. This sight can be ruined by the presence of black leaves. Let us look at the reasons why Hydrangea Leaves would be Turning Black.
Fungal diseases
The hydrangea leaves are affected by a lot of fungal diseases. Below are the major diseases that can cause the leaves of the hydrangea to turn black the most.
Botrytis Cinerea
Botrytis Cinerea is a fungal disease that causes big black spots on the leaves. If the intensity of this fungus is severe and it spreads rapidly, the leaves can turn almost entirely black.
This fungal disease can cause severe damage to the plant.
Powdery mildew
Powdery mildew is a fungal disease that causes the leaves of the hydrangea to turn black in places. When the leaves are blackened, you will see white dust on top of the leaves.
Cercospora Leaf Spot
If the leaves of your plant get wet from the rain or sprinklers and stay that way for some time, the Cercospora leaf spot can develop.
This disease will not kill your plant, but the leaves of your plant will droop and fall off. Hydrangeas affected by this disease might have lesser flower buds and blooms during the flowering season.
It can begin in the part of the plant and spread to the other parts.
Anthracnose
A hot, humid climate can lead to the development of anthracnose. This disease attacks the leaves and flowers of the hydrangea.
It leaves black spots all over the plant. It doesn’t spread everywhere from one point, rather, it develops all over the plant at the same time.
Solutions
A solution for growing fungus is to make sure that there is good circulation of air around the plants. Fungus grows mostly in humid and moist places, so a good airflow will ensure that the humidity dries up.
Also, clean up any plant debris near the plant. Removing some of the older stems can also help increase the air circulation and dry the plant. Do not remove more than 1/3rd of the stems of the plant.
Spray fungicide on your hydrangeas. Fungicides containing copper or chlorothalonil are effective against fungus.
If the infection is in the early stages, you can remove the infected leaves and dispose of them off properly so that they do not infect any other plant. Do not add any diseased part to your compost.
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Not enough phosphorous
A lack of phosphorous can result in the blackening of leaves in the hydrangea.
Phosphorous is one of the main elements of the soil in every plant. If it is not sufficient, it can cause the leaves to turn black, starting from the tips.
Solution
To know if the problem with your plant is a lack of phosphorous, you can get a soil testing kit or test your soil in a lab.
You should also check the acidity of the soil. If the pH is below 6.0, your soil is acidic. If the soil is acidic, the plant may not be able to absorb the phosphorous.
You will need to balance the acidity of the soil and make it more neutral. You can try to lower the acidity of the soil by using a small amount of garden lime.
If it does not work and the leaves continue to turn black even after more than a month, try using a phosphorous fertilizer. There are many organic, good-quality fertilizers available in the market.
Too much sunlight
Hydrangeas don’t need direct sunlight to grow. They need only partial sunlight and can grow in shade or partial shade. This is true at least for Hydrangea Macrophylla, which cannot thrive with full sunlight.
On the other hand, Panicle hydrangea can stay in direct sunlight for many hours and it is quite rare for the leaves of this species to burn because of sunlight.
If your hydrangea is in a place that receives direct sunlight for the whole day, the leaves of the plant will soon start to turn dark brown or black. The inflorescence can also shrivel and burn.
Damage because of sunlight is not very critical if your hydrangea is planted in the ground. However, if your hydrangea is planted indoors or in a pot and exposed to direct sunlight, it can even die due to sunburn.
Solution
The solution for sun damage is to move your plant away from the sun and into the shade.
If you cannot move your plant, you can use a garden umbrella to provide it with shade. Also, water the soil as soon as it dries up a bit.
If you can move your plant, keep it in a shaded place for the rest of the season. Move it to a place where it gets some indirect sunlight only when spring starts.
Frost damage
The ideal temperature for a hydrangea plant is 65-80 °F (18-26 °C). Temperature changes can affect your plant in negative ways.
If there is a sudden frost or a late frost in late spring, there can be too much moisture in the air. Further droplets from the frost can also collect on the leaves, causing the leaves of the hydrangea to turn black around the edges.
If the hydrangea plant has already grown new leaves in spring, they can especially suffer.
The damage will depend on how hard the frost was. If the frost was light, the tips of the mature leaves will turn black and the younger leaves on the upper part of the plant could die.
But if the frost was hard, the entire leaf blade can turn black. It will first become pale, then blacken, and in the end, start drooping.
Solution
If there is a sudden frost and you did not know about it, the only thing you can do is to remove the damaged leaves and wait for your hydrangea to recover. You can also use some liquid fertilizer while watering your plant.
Keep a lookout for weather forecasts. If the forecast suggests a frost, cover your hydrangea with garden fabric that you can remove once the frost is gone.
Issues with watering
There are three things that can go wrong when it comes to watering hydrangeas.
Overwatering
Hydrangea plants like water, but too much of it can cause problems. Overwatering hydrangeas can cause the leaves of the plant to turn black.
This is because overwatering can cause drainage problems for the soil. The plant will not be able to soak up excess water, which then remains stagnant on the soil.
Keeping the soil wet and waterlogged for a long time will start to damage the roots. It can cause root rot.
The roots will turn mushy and black. This damage slowly travels to the upper parts of the plant and starts to damage the stems and the leaves. This causes black spots, black leaves, discolored leaves, etc.
The excess water is also a cause for fungi to thrive.
Underwatering
Providing inadequate water to your hydrangea plant can also cause the leaves to turn black. If you do not give your plant enough water, the plant will start to dry up.
The leaves will start drooping and turn yellow. A hydrangea plant that has not been watered sufficiently can be a target for powdery mildew. One of the symptoms of powdery mildew is the blackening of leaves.
Improper watering technique
There is a right way to water your hydrangea, and if you do not water your plant properly, it will be affected.
If you water your hydrangeas from the top directly on the leaves, or if you have an automatic watering machine that does that, the water on the leaves may not dry up easily.
If the water stays on the leaves for a long time, it will be a breeding ground for various fungi. This will lead to black spots on your leaves.
Solutions
Here are a few tips that can help.
- Water your hydrangeas only when the soil around them is one inch dry.
- Water around the plant, not directly over the plant.
- Try to avoid overhead sprinklers while watering hydrangeas. Water at the base of the plant using garden hose or a drip system.
- If you have to use sprinklers, use them early in the morning so that the water has time to dry off during the day.
- Install a good drainage system. This will help you remove excess water from the soil.
Overfertilization
Using too much fertilizer can also cause the leaves of your plant to turn black, especially if it has a larger amount of nitrogen.
With too much nitrogen in the soil, the hydrangea plant will grow very quickly. This will not give enough time for the plant to mature and grow properly.
The leaves will be soft and prone to diseases. They will blacken easily.
Overfertilization can also cause something known as fertilizer burn. This means that excess use of fertilizer can actually burn the leaves of the plant.
Solution
If the leaves of your plant are turning black because of overfertilization, you need to stop fertilizing the plant.
Remove the damaged leaves from the plant.
If the hydrangea is growing in a pot, provide it with plenty of water so that it flushes out the excess fertilizers from the soil.
Do not fertilize your plant more than three times a year. Use a slow-release fertilizer. Avoid using fertilizers in winters.
Pests
The hydrangea plant attracts a lot of insects. The aphid is one of the insects that plague the hydrangea.
It latches itself on the underside of the hydrangea leaves and feeds on the sap and the green tissues of healthy plants. The aphids secrete a residue known as honeydew on the leaves.
Hydrangea leaves with honeydew can be a breeding ground for a fungus known as sooty mold.
If the aphids have infested the plant in large numbers, there is a possibility that the lower leaves of the plant can become completely black.
Solution
Spray the plant with some horticultural oil to get rid of the aphids. You can use neem oil.
Neem oil also repels a lot of pests that trouble the hydrangea. You can also use fungicide or insecticidal soap to help remove the fungus.
