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Why Are My Hydrangea Leaves Turning Black?

I’m excited to share my hydrangea-growing experiences with you today! If you’ve ever noticed your hydrangea leaves changing color, you’re not alone. This can happen for a few reasons. Let’s dive into what these reasons are and how to tackle them.

When hydrangea leaves turn black, it’s usually due to not enough water, too much water, fungal infections, frost, or incorrect fertilizing. Here’s a quick fix guide: Water your hydrangeas when the top 1-2 inches of soil feel dry. Protect them from frost and feed them 2-3 times a year with a slow-release, all-purpose fertilizer. This should help keep those leaves looking healthy and green.

Frost Damage

Frost damage

Hydrangea leaves turning black because of late frost damage.

Hydrangeas thrive best in temperatures between 65-80 °F (18-26 °C). But watch out for those late spring frosts! If your hydrangeas have sprouted young leaves and a frost hits, they’re likely to get damaged.

The extent of damage depends on how severe the frost is. In a heavy frost, you’ll see the leaves first turn pale, then blacken and droop. A lighter frost might only blacken the tips of mature leaves, killing the young ones at the top.

Here’s what you can do:

  1. Remove any damaged leaves to help your hydrangea recover.
  2. Give your hydrangea a one-time dose of liquid fertilizer.
  3. Keep an eye on the spring weather. If it looks like it’s going to get chilly, cover your hydrangea with garden fabric to protect it.

Insufficient Water

Hydrangea leaves turning black because of insufficient water.

Hydrangea leaves turning black because of insufficient water.

Overwatering is a big no-no as it can cause root rot in hydrangeas. Once the roots are weakened, leaf fungal diseases can swoop in, turning the leaves black.

Here’s what you can do:

  1. Water your hydrangeas only when the top inch of soil around the roots is dry.
  2. Aim to water the soil directly, rather than the leaves of the hydrangea. This helps prevent diseases.

Fungal Diseases

Disease

Hydrangea leaves turning black because of disease.

Hydrangeas can be hit by various diseases that lead to black spots on the leaves, with powdery mildew being a common culprit. This disease shows up as a white dust on top of the blackened leaves.

Here’s what you can do:

  1. Ensure there’s good airflow around your hydrangea plants.
  2. Clean up any fallen leaves or debris near the hydrangeas.
  3. Treat the plants with a fungicide. Look for ones containing copper or chlorothalonil, as they’re effective against this issue.
  4. If any leaves are heavily affected, it’s best to remove them.

Not Enough Phosphorus

Hydrangea leaves turning black because of a lack of phosphorus.

Hydrangea leaves turning black because of a lack of phosphorus.

When hydrangea leaves start darkening, often from the tips, it could be due to a lack of phosphorus in the soil. Phosphorus is crucial for plants, and a deficiency can cause leaves to turn a brownish-black or violet-black color, not just pure black.

Here’s what you can do:

  1. First, test the soil’s acidity. If the pH is below 6.0, the soil is too acidic.
  2. To reduce acidity, add a bit of garden lime to the soil.
  3. Finally, apply a phosphorus-rich fertilizer to give your hydrangeas the nutrients they need.

Too Much Sunlight

Hydrangea leaves turning black because of excessive sunlight

Hydrangea leaves turning black because of excessive sunlight.

Most hydrangeas, particularly the Hydrangea macrophylla variety, do best in just partial sun. Full sun isn’t ideal for them. However, Panicle hydrangeas are more sun-tolerant and rarely suffer leaf burn.

If your hydrangea is in full sun all day, you might notice the leaves burning, turning black or dark brown. Even the flowers might burn and shrivel.

Here’s what you can do:

  1. Create some shade for your hydrangea.
  2. Water the plant once the top 2 inches of soil have dried out.
  3. Consider moving it to a spot with less sun when spring rolls around.

Overfertilization

Using too much fertilizer, especially nitrogen-heavy ones, can harm hydrangea leaves. They might burn, turning black or dark brown.

Here’s what you can do:

  1. Cut back on fertilizing.
  2. Water your hydrangea deeply. This helps wash away excess fertilizer in the soil.
  3. Prune off any blackened leaves.
  4. Stick to fertilizing your hydrangea no more than three times a year, using a slow-release fertilizer.

Pests

Hydrangea leaves turning black because of aphids.

Leaves turning black because of aphids.

Hydrangeas can attract various insects, aphids being a common one. These pests cling to the underside of the leaves, feeding on the sap. Aphids excrete a substance called honeydew, which can drip onto the leaves below.

This honeydew-covered foliage becomes an ideal spot for sooty mold to develop, a disease that appears as black spots where the aphid secretions have landed.

Here’s what you can do:

  1. Use horticultural oil to spray the hydrangea, targeting the aphids.
  2. For the blackened leaves, apply a fungicide to manage the sooty mold.

patty flanagan

Wednesday 31st of May 2023

pictures were helpful when trying to decide what is causing leaves to turn black