Holes on Hydrangea Leaves – Reasons & Treatments

Hydrangeas are flowering plants known for their large, vibrant blooms. They sometimes develop holes in their leaves. Various factors, including pests, diseases, and environmental stressors, can cause these holes. Understanding the reasons behind the damage is crucial for maintaining the health and beauty of hydrangea plants.

What are the Most Common Causes of Holes in Hydrangea Leaves?

Hydrangeas are popular flowering shrubs with big, colorful blossoms. Sometimes, their leaves develop holes. Holes in hydrangea leaves can be alarming as they may signal health issues for the plant. Understanding the most common causes is important for gardeners who wish to keep their hydrangeas healthy.

• Pests: Tiny insects like slugs, aphids, beetles, and caterpillars often eat the leaves, causing holes.
• Disease: Fungal infections can cause spots that turn into holes.
• Physical Damage: Wind, hail, or accidental contact can tear the leaves.
• Nutrient Deficiencies: Poor soil can weaken the leaves, making them easier to damage.

By identifying the cause, a gardener can take the right steps to protect their hydrangeas and ensure that they thrive.

Pests Eating Hydrangea Leaves

There are three common pests on hydrangeas, that can cause holes in the leaves, or they can eat entire leaves, leaving hydrangeas partially or completely defoliated.

– Slugs

Slugs are one of the culprits when it comes to holes on hydrangea leaves. While slugs primarily feed on decaying materials, when not available, they will not shy away from hydrangea leaves.

They prefer cool, wet conditions, so the moist soil of hydrangeas is a welcoming environment for them.

Slugs are mostly active at night, so if you suspect that the holes on your hydrangea’s leaves are caused by slugs, you should check the shrubs at night to confirm.

But even in daylight, you can identify them by the trail of shiny mucous they leave behind on the leaves.

Slugs will devour leaves by working inward from the edges. Young growths can be chewed down all the way to the stem.

They can hide in crevices, under mulch, dense vegetation, and reproduce rapidly, so they can and will cause trouble if not properly dealt with.

– Caterpillars

Caterpillars are another threat to hydrangea leaves. Of all the caterpillars, the leaf-tier or celery leaf-tier moth’s larvae are especially fond of hydrangea leaves.

These primarily attack Annabelle’ hydrangea (Hydrangea arborescens ‘Annabelle’) and other smooth hydrangeas.

Besides munching on the leaves of hydrangeas, they also have the habit of gluing together hydrangea leaves. This is a smart defense mechanism from potential predators.

These caterpillars morph into a chrysalis in 10 days or so, then turn into adult moths after a week or so.

The moth then lays eggs again in late fall on the stem of hydrangeas, where the eggs overwinter, and in spring the whole process starts anew.

– Rose Chafers

These are a type of beetle that you’ll usually find on roses, but they also attack hydrangeas and many other flowering plants.

Unlike the other pests I discussed, rose chafers take to the blooms of hydrangeas particularly, but they also eat leaves, causing holes on them.

You can identify rose chafers (Macrodactylus subspinosus) by their tan bodies and long orange legs.

You’ll find them munching on the blooms and leaves of your hydrangeas, leaving behind large irregularly shaped holes.

Now that you can identify the pest causing holes on hydrangea leaves, let’s see what you can do about protecting hydrangeas from these pests or treating an ongoing infestation.

Protect Hydrangeas from Pests

The three main culprits causing holes on hydrangea leaves and bloom are slugs, caterpillars and rose chafers. Here’s how to get rid of each and prevent them from coming back.

How to keep slugs away:

• The soft bodies of slugs easily get hurt by sharp fragments of crushed oyster shells, sharp sand, sawdust, or diatomaceous earth (this is even lethal to them). Create a barrier of about 2-foot wide around your hydrangeas and keep it dry by replenishing it to keep slugs and snails away.
• Avoid mulch in your garden as they can attract slugs
• You can set traps (cups of milk, beer or yeast dissolved in sugar water), although some of them may attract even more slugs
• Keep ducks in your garden, they’re a natural predator of slugs
• Avoid using metaldehyde, which is a poison. It’s not very effective and can be dangerous for birds and other slug predators
• Removing slugs by hand is the easiest way to deal with an ongoing infestation, but inspect your hydrangeas at night, when slugs are most active

How to keep caterpillars away:

• Because the leaf-tier moth lays its eggs on the stems of hydrangeas in late fall and because it picks hydrangeas that grow on new wood, it’s a good idea to cut back your hydrangea in early spring as close to the ground as possible (leave only about 4 inches of the stem), thus removing any eggs that are still on the stems
• Alternatively, you can spray the stems with a biological insecticide that contains Bacillus thuringiensis kurstaki. Spray as soon as you see new growths on your hydrangea. The insecticide will kill caterpillars emerging from the eggs
• You can deal with an ongoing infestation by opening stuck leaves one by one and crushing the caterpillar

How to keep rose chafers away:

• Avoid using sandy topsoil in your garden because they lay their eggs in sandy soil
• They enjoy sunny spots and dry soil, so adding more trees and shrubs that help shade your garden also helps
• Growing a lawn with a high clover content will also help keep these pests away
• Introducing nematodes into your garden will help destroy rose chafers larvae
• An ongoing infestation can be controlled by hand-picking rose chafers or vacuuming them with a hand-held vacuum and putting them in soapy water

Hail Damage on Hydrangea Leaves

A hailstorm can leave the soft leaves of your hydrangea all torn up and shredded, making it easy to mistake for insect damage.

Therefore, a hailstorm can also cause holes on your hydrangea leaves. Unfortunately, you can’t do anything to prevent hailstorms.

Most plants, including hydrangea, will survive hailstorms, it’s just that their leaves will be damaged.

Nutrient Deficiencies

Plants need various nutrients to stay healthy. When hydrangeas lack these essential nutrients, their leaves can develop holes. This situation, known as nutrient deficiency, might occur for a few reasons.

For example, if the soil doesn’t have enough of a certain nutrient, the plant can’t get what it needs. This can lead to weak leaves that easily get damaged. The key nutrients that can lead to leaf problems when missing are:

• Nitrogen
• Phosphorus
• Potassium
• Calcium
• Magnesium

However, other factors such as pests or diseases also cause holes in hydrangea leaves. Therefore, it is important to correctly identify the problem. If nutrient deficiency is the cause, using the right fertilizers can help the plant heal and prevent further issues.

What to do With Damaged Hydrangea Leaves?

When a hydrangea plant has holes in its leaves, it means the leaves are damaged. To deal with this, you should:

• Remove the damaged leaves by cutting them off with clean, sharp scissors.
• Look for pests, like slugs or caterpillars, that may be eating the leaves.
• Use insecticidal soap or a natural remedy, like neem oil, to treat pests.
• Improve the health of the plant with good care, including proper watering and fertilizer.
• Provide the right amount of sunlight and protect the plant from harsh weather.