Hamamelis Leaves Curling
Witch hazel aphid and powdery mildew are the most common reasons hamamelis leaves curl. This guide shows you how to identify each cause and keep your witch hazel vigorous and blooming.
1. Witch hazel aphid (Hormaphis hamamelidis)
The witch hazel aphid has an unusual lifecycle that involves alternating between hamamelis and birch trees. It overwinters as eggs on hamamelis bark and hatches in spring as the leaves emerge. The feeding of the first generation creates distinctive distorted galls on young leaves; later generations migrate to birch, returning to witch hazel in autumn to lay overwintering eggs. It is the most common cause of puckered, distorted hamamelis leaves in UK gardens.
What to look for
Young leaves in spring develop conspicuous cone-shaped or rosette-like galls, or the whole leaf may be tightly crinkled, puckered, and distorted. The distortion appears just as the new leaves unfurl and can be alarming in its severity. The galls are green initially but may turn red or yellow with age. Once the aphids migrate to birch in early summer, no new distortion occurs, but the already-deformed leaves carry the symptoms until they drop in autumn.
What to do
The distortion is cosmetic and does not seriously harm an established hamamelis. If you want to limit the population, spray the emerging buds and young leaves with a plant-based insecticidal soap or horticultural oil in early spring just as buds begin to open, before galling begins. Once galls have formed, sprays cannot reach the aphids inside and treatment is futile. For a long-term reduction in the population, consider removing any birch trees within a few metres as these serve as the summer host. Do not cut off galled leaves as this removes a significant portion of the plant's foliage.
2. Powdery mildew
Powdery mildew affects hamamelis most often in warm, dry summers with cool nights, and is particularly common on plants growing in sheltered or enclosed positions where air circulation is poor. The disease does not usually cause serious harm but is unsightly and can weaken the plant if it occurs repeatedly.
What to look for
A white or pale grey powdery coating appears on the upper surface of leaves, particularly on young growth. Infected leaves curl upward and inward at the margins and may appear slightly distorted. The coating can be rubbed off with a finger. Heavily infected leaves may turn yellow and drop early, reducing the quality of the autumn colour display for which hamamelis is prized. Buds on infected shoots may also be affected, reducing the following winter's flower display.
What to do
Improve air circulation around the plant by removing any crowding vegetation nearby and by thinning the centre of the shrub after flowering. Remove and bin affected leaves and shoots. Water at the base of the plant in the morning so foliage stays dry during the day. A fortnightly spray of diluted milk (one part whole milk to nine parts water) from the first signs of infection is an effective and environmentally safe treatment. Sulphur-based fungicides work well as a preventive measure applied from late spring in gardens where mildew is a recurring problem.
3. Vine weevil (Otiorhynchus sulcatus)
Vine weevil is a widespread garden pest that affects a huge range of ornamental shrubs including hamamelis. The adult beetles notch leaf margins and the C-shaped larvae feed on roots in the compost or soil. It is the larval damage that causes the most serious harm, killing plants by destroying the root system.
What to look for
Characteristic irregular notches cut from the margins of leaves are the work of adult vine weevil beetles, which feed at night and hide in leaf litter or compost during the day. This leaf damage is unsightly but not usually serious. More serious is the wilting and general decline that occurs when larvae attack the roots; the plant looks drought-stressed even after watering, leaves curl, and the plant may eventually collapse. If you tip a container-grown hamamelis out of its pot, white C-shaped grubs in the compost confirm vine weevil.
What to do
For container plants, apply parasitic nematodes (Steinernema kraussei) to the compost in late summer and again in early autumn when soil temperature is between 5 and 20 Celsius. Replace heavily infested compost and treat the new compost before repotting. For garden plants, apply nematodes to the soil around the base of the shrub in the same period. Trap adult beetles by placing sticky traps or corrugated cardboard rolls near the plant at night; the beetles hide in these during the day and can be collected and destroyed. Removing leaf litter and debris around the plant reduces hiding places for adults.
4. Iron deficiency (lime-induced chlorosis)
Hamamelis is a calcifuge plant that needs acidic to neutral soil (pH 6.0 to 7.0) to thrive. In alkaline or chalky soil, or when lime has been inadvertently incorporated into the planting area (from mortar rubble, chalk paths, or liming of an adjacent vegetable patch), the plant is unable to absorb iron even when it is present in the soil, because iron becomes chemically unavailable at high pH.
What to look for
Leaves develop a yellowing between the veins while the veins themselves remain green, a symptom known as interveinal chlorosis. This is most obvious on young leaves at the shoot tips, which are the most actively growing and therefore most dependent on a consistent supply of nutrients. Severely affected leaves may turn almost entirely pale yellow or cream and may curl at the margins. Overall growth becomes stunted and the plant produces few flowers.
What to do
Test the soil pH with a simple kit from a garden centre. If it is above 6.5, the most practical remedy is to apply a sequestered iron (iron chelate) product as a soil drench and foliar spray in spring and again in midsummer, following the manufacturer's instructions. This makes iron available in a form the plant can absorb regardless of soil pH. For a longer-term solution, mulching with acidic materials such as pine bark or composted wood chip and applying sulphur chips to the soil around the plant will gradually reduce pH over several seasons. Avoid planting hamamelis on chalk or very alkaline soils where a structural solution is not practical.
5. Drought stress
Hamamelis naturally grows at woodland edges and in moist, sheltered spots and dislikes prolonged drought. Container-grown specimens, which are very popular because of the expense of field-grown plants, are particularly prone to drying out, especially when the plant is in full leaf during summer and the demand for water is highest.
What to look for
Leaves curl inward and take on a dull, slightly grey-green tone. In more severe drought the leaf margins and tips turn brown and crisp. Container plants in particular may droop visibly within a day or two of hot weather if not watered. In extreme cases the entire plant wilts despite the root ball still holding some moisture, because the root hairs have died back and can no longer take up water efficiently.
What to do
Water container hamamelis thoroughly every day in warm summer weather, and ensure the pot has adequate drainage holes so roots do not sit in water. If the compost has dried out and is repelling water, stand the pot in a tray of water for an hour to allow it to rehydrate from below. Repot into the next size of container each spring to give roots more moisture-retaining volume to draw from. Mulch garden plants with a 100 mm layer of acidic organic material such as bark chip to conserve soil moisture and keep roots cool. Choose a planting site that retains soil moisture and is sheltered from drying winds.
Frequently asked questions
Why are my hamamelis leaves puckered and distorted?
Puckered, distorted leaves on hamamelis in spring are most often caused by witch hazel aphid (Hormaphis hamamelidis), which creates distinctive cone-shaped or rosette galls on young leaves. The distortion caused in spring persists on the same leaves through the summer even after the aphids have gone.
Why are my witch hazel leaves turning yellow between the veins?
Yellowing between the veins while veins remain green (interveinal chlorosis) on hamamelis almost always indicates iron deficiency caused by alkaline or chalky soil. Hamamelis is a lime-sensitive plant that cannot access iron when soil pH is too high. Test your soil pH and treat with sequestered iron chelate if it is above 6.5.
How do I stop vine weevil damaging my hamamelis?
Apply parasitic nematodes (Steinernema kraussei or Heterorhabditis bacteriophora) to the soil or compost in late summer or early autumn when soil temperature is above 5 Celsius. This is the most effective biological control for vine weevil larvae. For adult vine weevils that notch leaf margins, go out after dark with a torch and collect them by hand.
Can hamamelis grow in clay soil?
Hamamelis tolerates heavy soils better than many ornamental shrubs but performs best in moist, humus-rich, well-drained soil. In dense clay it grows more slowly and is more susceptible to root problems in wet winters. Improving clay soil with plenty of organic matter before planting makes a significant difference to long-term performance.
Why is my hamamelis not flowering well?
Poor flowering on hamamelis is most often caused by planting in too much shade (it needs at least dappled light for good flowering), soil that is too alkaline (causing nutrient stress that suppresses flower bud development), or hard pruning at the wrong time. Hamamelis flowers on bare wood in winter; prune only immediately after flowering to avoid cutting off next year's buds.
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