About wintersweet
Chimonanthus praecox is one of the most cherished shrubs in the UK winter garden. It produces small but intensely fragrant waxy yellow flowers, each with a distinctive purple-stained centre, on bare leafless stems in January and February. The scent carries on still winter days even in cold weather and a single established plant can perfume an entire garden. The cultivar 'Grandiflorus' has larger flowers; 'Luteus' has clear yellow flowers without the purple staining. In summer the plant produces large, lance-shaped, somewhat rough-textured leaves before the whole cycle begins again.
Wintersweet is traditionally grown against a south or southwest-facing wall, which helps the wood ripen over summer and encourages reliable flowering. It is a slow grower, typically reaching one to two metres in the first ten years, but it is very long-lived and an established specimen can flower prolifically for many decades.
Cause 1: Aphids on new growth
The most common reason wintersweet leaves curl is an infestation of aphids, particularly the peach-potato aphid (Myzus persicae). Colonies build up on the soft new shoot tips and undersides of young leaves in spring and early summer, causing the leaves to curl tightly downward and inward around the insects. The growth is distorted and may feel sticky to the touch.
The stickiness comes from honeydew, a sugary waste product excreted by aphids as they feed on plant sap. Honeydew quickly attracts sooty mould, a black fungal coating that further weakens the leaves by blocking light. If you peel back a curled leaf you will usually find the aphids inside, ranging in colour from pale green to yellow.
On established wall-grown plants aphid outbreaks tend to be self-limiting once natural predators such as ladybirds, lacewings, and parasitic wasps arrive in numbers, usually by midsummer. You can speed things along by squashing colonies by hand or washing them off with a strong jet of water. Avoid systemic pesticides on flowering shrubs if you can: the flowers that follow the next January are an important early nectar source for pollinators. On young plants in their first few years, where an aphid attack can set back growth more significantly, a targeted spray with a fatty acid or plant oil insecticide is a reasonable option.
Cause 2: Drought stress
Wall-grown plants are at serious risk of drought stress, even in a UK summer. A south-facing wall creates a pronounced rain shadow: the wall itself deflects rainfall away from the soil directly at its base, and the masonry absorbs and radiates heat that dries the ground further. Wintersweet has large leaves with a relatively high water demand in summer, and a plant that is not getting enough moisture will respond by curling its leaves inward to reduce the surface area exposed to sun and wind.
Drought-stressed leaves also begin to yellow and may drop well before autumn. The curling tends to affect all the foliage rather than just the soft new growth at the tips, which helps distinguish it from an aphid problem. If the soil immediately around the plant's base is bone dry a few centimetres down, drought is your answer.
Water deeply at the base rather than little and often: a thorough soak once or twice a week in dry spells is far more effective than a daily splash. Apply a generous mulch of bark chippings or well-rotted compost in a wide ring around the plant each spring, keeping it clear of the stem itself. This retains moisture, moderates soil temperature, and suppresses weeds that would otherwise compete for water.
Other causes to consider
Powdery mildew. In dry summers, particularly against walls where air circulation can be poor, wintersweet is susceptible to powdery mildew. A white or pale grey dusty coating appears on the upper leaf surface, followed by curling and yellowing. Consistent watering reduces susceptibility. Remove the worst-affected shoots and thin congested growth after flowering in early spring to improve airflow.
Scale insects. Older wall-trained stems can harbour scale insects, particularly cushion scale or brown scale. They appear as small waxy or shell-like bumps on the bark and stems. Heavy infestations weaken the plant and produce honeydew and sooty mould. Treat in late winter with a plant oil-based winter wash while the plant is dormant.
Late frost damage on flowers. Chimonanthus praecox flowers in January and February when hard frosts are still common. A severe frost can kill or brown the open flowers before you have had a chance to enjoy them. The leaves produced later in summer are not affected, but the loss of that year's flowers is disappointing. If a hard frost is forecast while the plant is in bud, covering it overnight with a double layer of horticultural fleece will usually protect the blooms.
Coral spot. Dead or dying wood on wintersweet can attract coral spot fungus (Nectria cinnabarina), which appears as small bright orange-pink pustules on dead stems. Prune out affected wood cleanly back to healthy growth and dispose of it rather than composting it.
Waterlogging. Although wintersweet tolerates a range of soils it dislikes waterlogged roots. Poor drainage causes root death, which manifests as general decline, yellowing leaves, and die-back of branches. Improve drainage before planting or raise the planting site slightly.
Prevention and long-term care
Plant wintersweet against a warm south or southwest-facing wall in a well-drained soil with reasonable fertility. Water and mulch generously every spring, paying particular attention to the rain shadow zone directly at the wall's base. Check the soft new growth regularly from late April onwards for the first signs of aphid colonies and deal with them early before numbers build. If late frosts threaten while the plant is in flower, have a roll of fleece on hand. Prune only lightly and immediately after flowering in late winter: cutting back hard reduces the following season's flower buds.
Above all, be patient. Wintersweet is genuinely slow to reach its potential, but a mature established plant flowering in the depth of winter with a fragrance that carries across the whole garden is one of the great rewards of UK gardening.
Frequently asked questions
Why are my wintersweet leaves curling downward?
Downward curling on new growth in spring and summer almost always points to aphids, particularly the peach-potato aphid (Myzus persicae). Check the undersides of the leaves and the soft shoot tips for clusters of small green or yellow insects. Sticky honeydew residue and a black sooty mould coating are further confirmation.
Can drought cause wintersweet leaves to curl?
Yes, and it is one of the most common problems for wall-grown plants. The soil at the base of a south-facing wall sits in a rain shadow and can become very dry even after moderate rainfall. Leaves curl inward, lose their deep green colour, and may drop early. Water deeply at the base and apply a generous mulch of bark or compost each spring to retain moisture.
Why hasn't my wintersweet flowered yet?
Chimonanthus praecox is famously slow to reach flowering maturity. Seed-raised plants typically take 4 to 8 years before producing their first blooms. Grafted plants sold by specialist nurseries can flower a year or two sooner. Growing the plant against a warm south or southwest-facing wall helps ripen the wood each summer, which is what triggers good flowering the following January or February. Be patient: once established, wintersweet can flower prolifically for decades.
Could powdery mildew cause the leaves to curl on my wintersweet?
It can, especially on wall-trained plants where air circulation is limited and the soil tends to dry out. Powdery mildew appears as a white or grey dusty coating on the leaf surfaces, often accompanied by curling and early yellowing. Keeping the plant well watered reduces susceptibility. Remove badly affected shoots and improve airflow by thinning congested growth after flowering in early spring.
Will a hard frost damage my wintersweet?
The plant itself is hardy throughout the UK, but the flowers are vulnerable. Chimonanthus praecox blooms on bare stems in January and February, and a severe frost during or just before flowering can destroy the blooms before you get to enjoy their extraordinary fragrance. If a hard frost is forecast while the plant is in bud or flower, drape a double layer of horticultural fleece over it overnight and remove it during the day. The leaves that follow in summer are not frost-sensitive.