Why Are My Hydrangea Leaves Turning Black?

Today I am going to share with you my experience of growing hydrangeas. Very often with these plants, various problems lead to a change in the color of the leaves. There are several causes for this. Here you will learn what to do in each case.

Insufficient water, overwatering, fungal diseases, late frost damage, or improper fertilization are the most common causes of hydrangea leaves turning black. To fix the blackening of the leaves, water hydrangeas when the soil is 5-10% dry and it should be well-drained. Cover the hydrangea for the cold and fertilize it 2-3 times per season with a slow-release multipurpose fertilizer to keep the leaves from turning black.

Insufficient water

Too much watering will certainly lead to root rot. Hydrangeas weakened by root rot can easily be attacked by leaf fungal diseases, which will cause the leaves to turn black.

Next is inadequate watering. In this case, the leaves will droop and turn yellow at the tips. Hydrangea that has experienced drought stress can be an easy target for powdery mildew. One of the symptoms of this disease is the blackening of the leaves.

Finally, improper watering technique. If you water the hydrangea constantly on the leaves or the automatic waterer does it. Sooner or later on the leaves will appear black spots (fungal disease).

To solve this problem, you should water your hydrangeas only when the soil around the roots is 1 inch dry and not later. When watering, try to water the soil around the hydrangea, not the hydrangea itself.

Fungal diseases

Several diseases can affect hydrangea leaves, resulting in black spots. But the two most common diseases cause the leaves to turn black the most.

The first is Botrytis Cinerea. This is a fungal disease that makes big black spots on the leaves. If it spreads severely, the leaves can turn almost completely black. The result of the disease is severe damage to the plant.

The second disease is powdery mildew. This, too, is a fungal disease that causes hydrangea leaves to turn partly black. The feature is white dust on top of blackened leaves.

To treat hydrangeas for both diseases, make sure there is good air circulation around them. Clean up any plant debris near the hydrangeas.

The next thing you need to do is spray hydrangeas with fungicide. Products containing copper or chlorothalonil work well with these diseases.

The recovery process can take a long time. You will need to remove the heavily infested leaves. You may also need to re-spray with fungicide.

Not enough phosphorus

The next reason for the darkening of hydrangea leaves is a lack of phosphorus in the soil. This is one of the three most important elements for every plant. If it is not enough, the leaves will start to turn black from the tips. The color may not be pure black but slightly brownish-black or violet-black.

If these symptoms are similar to yours, the first thing you should do is check the acidity of the soil. And if the pH is below 6.0, you need to neutralize the excess acidity. In acidic soil, the phosphorus may not be absorbed by the plant.

You can lower the acidity of the soil with a small amount of garden lime.

If the new leaves continue to turn black after a month or two, you should use the phosphorus fertilizer. There are many good products on the market for this purpose.

Late frost damage

The best temperature for growing hydrangeas is 65-80 °F (18-26 °C). But nature does not always give us what we need and sometimes the unexpected can happen. Often in late spring, late frosts can occur and if the hydrangeas have already grown young leaves by this time, they will certainly suffer.

Depending on how hard the frost was, the damage will vary. In a hard frost, almost the entire leaf blade will first turn pale and then blacken and droop. If the frost was light, only the tips of the mature leaves will turn black and the young upper leaves will die.

If this is your case, all you can do is remove the damaged leaves and wait for the hydrangea to recover. You can also water it once with liquid fertilizer.

For the future, always keep an eye on the weather forecast in the spring. If a cold front comes in, cover the hydrangea with garden fabric. Once the threat is gone, the cover can be removed.

Too much sunlight

Most hydrangeas prefer only partial sun. This is especially true of Hydrangea macrophylla; full sun is contraindicated to it. Panicle hydrangea, on the other hand, can tolerate many more hours of direct sunlight, and the burning of its leaves is quite rare.

If your hydrangea grows in full sun all day, it can burn and the leaves will turn black or dark brown. The inflorescences may also burn and shrivel.

When hydrangeas are grown in the ground, sun damage is rarely critical. But if you grow hydrangeas in a pot in direct sunlight, they can die from sunburn.

If your hydrangea suffers sun damage, you should provide it with shade. You can do this easily with a garden umbrella. Next, you need to water it as soon as the soil dries out a little (no more than 2 inches).

Keep the hydrangea in the shade for the rest of the season and only transplant it to a less sunny location the following spring.

Over-fertilization

Too much fertilizer, particularly nitrogen, can cause leaf problems. The first thing that can happen is that the leaves will burn and can turn black or dark brown.

Also, with an abundance of nitrogen and other nutrients, the hydrangea will grow vigorously. Leaves will not mature properly and will be soft. As a result, they become diseased and blacken easily.

If this is your case, you need to stop fertilizing. If a hydrangea is growing in a container, water it generously, this will flush out any excess fertilizer from the soil. Remove any blackened leaves.

Fertilize the hydrangea no more than 3 times a year with a slow-release fertilizer. Do not fertilize over the winter.

Pests

Hydrangea leaves attract many insects, including aphids. This insect attaches itself to the underside of the leaves and feeds on their sap. The aphids produce honeydew that falls on the leaves below.

Hydrangea leaves covered with honeydew are a perfect breeding ground for the disease called sooty mold. This disease manifests itself as a black spot where the aphid secretions have fallen.

If the aphids are very widespread, the lower leaves can become almost completely black.

To remedy the situation, you must first spray the hydrangea with horticultural oil to get rid of the aphids. The second thing to do is to spray the black leaves with fungicide.

Key Takeaways:

• Hydrangea leaves turn black due to various diseases. Spray the hydrangea with fungicide.
• Insufficient phosphorus and too much fertilizer can cause the blackening of the leaves. Apply phosphorous fertilizer. Do the hydrangea not be fertilized more than twice a year.
• Too much direct sun can burn the leaves and they will turn black. Transplant the hydrangea to a more shady location.
• Late frosts can also cause the leaves to turn black. Cover the hydrangea for the duration of the frost.