Hydrangea shrubs are known for their flamboyant, colorful blooms, which stand out thanks to the backdrop of lush green foliage. So it’s more than a little obvious when something isn’t quite right about the leaves.
Curling leaves can appear ominous, but what’s behind this dramatic appearance change?
Curling hydrangea leaves can be caused by several issues including over or under-watering, dry soil conditions, weather extremes, nutrient deficiency, and damage from insects and fungal infections. These each contributes to weakened plant tissue and cell death, leading to distorted curled foliage.
Leaf curl can occur in whole or localized sections of leaf and is often accompanied by discoloration, texture changes, and other symptoms.
To help you troubleshoot them, we’ve listed the common causes and fixes plus prevention tips.
Curling Leaves in Hydrangea – 10 Possible Causes
With so many reasons behind their curling, it’s helpful to know more about each leaf curl culprit so you can spot the signs and apply the right fix.
1. Watering Issues
When under-watered, leaves turn crisp and brown due to dying, dehydrated cells, causing downward curling leaves. Overwatering can lead to leaf curl too, accompanied by yellowing due to suffocating the roots that the leaves depend on for nutrients.
Water the soil when the top inch is dry – no sooner and no later.
Hydrangea leaves curl upwards as a defense mechanism when attacked by certain diseases. Surface blights such as powdery mildew and leaf spot leach nutrients and appear as white mold and small rust-colored rings whilst the fungus Armillaria root rot prevents water transportation, causing leaves to ‘cup’ inwards.
Treat affected areas with natural fungicide spray and avoid overwatering.
Munching insects like aphids and Leaftier larvas (translucent/green caterpillars with black heads) disconnect the cell networks crucial for transporting nutrients and water, causing leaves to twist into a tightly curled pocket. Look out for sticky residue or lacy white webbing on the lower side.
Remove curled leaves and spray healthy leaves with Horticultural Oil.
4. Dry Soil
Hydrangea translates in Greek as “water vessel”, so even the slightest drought will cause leaf curl. In the summer heat, dried-out soil will eventually cause leaf tips to curl before they brown and blacken altogether.
Check the top inch of soil regularly with your finger – it should remain slightly moist at all times.
5. Nutrient Deficiency
A lack of phosphorus – a vital nutrient for photosynthesis, root health, and sturdy development – affects how well water is absorbed which causes not only upward curling but noticeable reddish and purple leaf staining.
Amend the soil pH to between 5.2-5.5 and apply an all-purpose slow-release fertilizer in early spring.
6. Sun Scald
Bigleaf hydrangeas grown in the south or those planted in a full sun spot of the garden risk sunburn. This sees the leaf tips turn grayish-brown and crisp before curling upwards to protect themselves from further scorching and water loss.
Trim burnt leaves and shade them from afternoon sun with a garden umbrella/another plant.
7. Frost Damage
Frost causes ice crystals to form inside the leaf tissue, killing off cells. Smooth and Bigleaf hydrangeas are particularly susceptible – mature leaves will display black blotches whilst developing leaves turn entirely black and curl into tight balls before falling off.
Remove damaged leaves and cover shrub with garden fabric before cold snaps are expected.
8. Transplant Shock
Replanting can cause trauma if done incorrectly. Nursery-grown hydrangeas acclimatize to a certain soil type and watering schedule and will notify their stress in your garden before long by displaying yellowing, twisted leaves.
Water thoroughly and provide a shade umbrella for the initial 2-3 weeks
9. Extreme Fluctuations in Temperature
Unusually-high winds in spring when the leaves have already begun developing can sap moisture from the leaves, resulting in crisp, downward curling, whilst heatwaves can cause brown-tipped upward curling leaves in reaction to water loss.
Prune back damaged leaves and water twice daily during hot, dry periods/provide wind cover.
10. Herbicide or Chemical Damage
Accidental herbicide splashback from use on your lawn can weaken a hydrangeas plant tissue and disrupt cell growth, resulting in pale, and crispy leaves that curl at the margins. Even selective herbicides applied to nearby soil can risk damage.
Horticultural Specialist Carol Reese suggests checking the label on herbicide products: “If it carries the number 365, this means it leaves residual chemicals in the soil and should not be used near the roots of ornamental plants or shrubs.”
Hydrangea Leaf Curl – Prevention Tips
Now you know the common causes behind leaf curl, all take a little vigilance and forward-thinking in caring for your hydrangeas to reduce the risks:
- Use organic, well-draining soil. This keeps things moist while taking care of accidental overwatering that can lead to root rot
- Find out the frost dates in your local area so you can apprehend temperature changes in time
- Buy hydrangeas with a large root system. Jean Carr of Gardening Calendar explains that “larger roots reduce the effects of transplant shock” due to greater nutrient uptake.
- Clean leaf debris around the base periodically and spray lower stems with organic fungicide to deter Leaftier egg-laying.
Will Hydrangeas Come Back After Wilting?
Hydrangeas naturally wilt near the end of their blooming period but will wilt and shed petals sooner under temperature extremes. To encourage healthy blooms the following spring, transplant dormant hydrangeas into pots in an unheated garage to winter them and prune back dead branches.
Can Hydrangeas Grow in Pots?
Hydrangeas grow well in pots provided they have well-draining soil, 4-6 hours of dappled sunlight, and regular watering to ensure the top inch remains moist. Choose planters at least 2ft wide to accommodate their aggressive roots as smaller pots can suffocate their growth.
In summary, hydrangeas experience curling leaves for various reasons from unbalanced watering to pest damage, funguses, and poor soil.
But the good news is that most of the above-mentioned issues can be spotted and remedied before any permanent damage is done.