Botanical Names: French hydrangea (Hydrangea macrophylla), lacecap hydrangea (Hydrangeamacrophylla normalis), Hydrangea serrata
Is your hydrangea looking less than stunning? Hydrangea pests and diseases aren’t usually too prevalent, but when that glorious flower show is interrupted, it’s tough not to panic. Learn about common hydrangea problems, including hydrangea leaves turning red. Discover easy solutions to these issues.
If you spot holes in leaves, you’re dealing with some hydrangea pests — likely some kind of caterpillar-type critter. A variety of what’s known as “fruit worms” like to munch on hydrangea leaves. They usually hang out underneath leaves, so if you look under leaves, you’ll probably spot the creatures. Knock them into soapy water or use a natural product containing spinosad, a type of bacteria.
On young hydrangeas especially, holes can also occur due to slug feeding. The best way to know if slugs are the culprit is to go out and check plants at night with a flashlight. You can also lay a rolled up newspaper near the base of the shrub. Slugs should crawl into and under it before daybreak, but they might just be visiting the bed, not feeding on the plant. Slug holes usually have ragged edges.
Many hydrangea problems can occur if plants aren’t receiving enough water. You might notice that flowers turn brown and die quickly. This can occur for a variety of reasons, but it’s common when hydrangea shrubs don’t receive sufficient water. Lack of water can also cause brown, brittle spots on leaf edges, and a few branches all on one side may die out. Usually this occurs when automated sprinkler spray isn’t reaching the entire hydrangea plant. Flowers that wilt during the day time and don’t perk up at night are also a sign of underwatering.
In spring and early summer hydrangea leaves can show black spots, especially during bouts of wet, rainy weather. This hydrangea problem appears severe, but it’s usually just a leaf-spot fungus that doesn’t really harm the plant. When the rainy time ceases, new growth shouldn’t have the spots. If black spots appear during drier times, you may be overwatering your hydrangea shrubs.
Hydrangea leaves turning red usually happens when plants are growing in full sun and have experienced a dry spell. Cool weather — on either end of the growing season — can also trigger a red-purple color in leaves. The other issue could be a phosphorus shortage in soil, especially if leaves turn more purple than red. If you’re trying to shift flower color, you could be inadvertently tying up the phosphorus in the soil. Do a soil test to check soil pH and follow the recommendations of the test results to adjust soil pH. You may be advised to apply phosphorus to soil.
Some hydrangeas show red leaf color in fall. Oakleaf hydrangea (Hydrangea quercifolia) in particular has a strong autumn color display, with leaves turning red and purple. The strongest colors develop in plants growing in full sun.
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