Neillia is one of those shrubs that garden designers reach for regularly but that most gardeners have never heard of. The two species most commonly grown in UK gardens, Neillia thibetica (Tibetan neillia) and N. sinensis (Chinese neillia), are elegant deciduous shrubs in the rose family (Rosaceae) that produce long, arching wands of tubular pale pink flowers in late May and June. The flowers are carried on gracefully curved stems, one to two metres tall, and the effect at peak flowering is something between a spiraea and a small-flowered weigela, but with a lightness and line that neither of those plants quite matches.
The leaves are a large part of the appeal. Deeply ribbed and with a pointed, slightly serrated edge, they give the whole plant a fine texture that reads well in a mixed border or against a fence or wall. N. thibetica holds an RHS Award of Garden Merit, which reflects its consistent performance across UK growing conditions, and both species are fully hardy throughout Britain. They are close relatives of spiraea and stephanandra, and they share those plants' general toughness and willingness to grow in a wide range of situations.
When those attractive ribbed leaves start to curl, it is worth investigating. Neillia is generally undemanding, and curling foliage usually points to one of two straightforward causes: powdery mildew or aphids. Drought stress is the other common factor, particularly in dry summers when the plant is growing in a rain shadow or in free-draining soil.
Powdery mildew
Powdery mildew is the most common disease on neillia and the most likely cause if you see curling and distortion on the leaves alongside a pale, floury coating. As a member of the Rosaceae, neillia is susceptible to Erysiphe and related powdery mildew species, and the large, deeply ribbed leaves make symptoms particularly visible compared to finer-leaved shrubs. The white powdery growth appears first on the upper surfaces of the leaves, then spreads to the undersides and, in severe cases, to the young stems and flower stalks. Affected leaves curl, pucker, and lose their fresh appearance, and the overall effect on a badly infected plant in late summer is of a shrub that looks tired and dull rather than the graceful, fine-textured specimen it should be.
Powdery mildew on neillia, as on most plants, is most common in warm, dry conditions. The fungal spores germinate on the surface of dry leaves and spread readily in still, warm air. Neillia planted in sheltered positions, particularly against a wall or fence or in a courtyard where air circulation is limited, is more susceptible than plants in more open positions. Drought stress and mildew reinforce each other: a plant short of water is less able to resist fungal attack, and mildew further reduces the plant's ability to photosynthesize efficiently.
The most effective first response is to improve airflow around the plant. Thin out any congested stems and, if the plant is growing in a sheltered position, consider whether there is anything in the surrounding planting that can be reduced to open up air movement. Water consistently at the base of the plant during dry spells, which reduces drought stress without wetting the foliage and creating conditions for additional fungal spread. Cut out badly affected shoots entirely after flowering, rather than just removing the affected leaves, because the fungal mycelium can persist in stem tissue and re-emerge on new growth. Apply a potassium bicarbonate spray or neem oil to affected foliage at the first sign of white coating, and repeat every ten to fourteen days through the risk period. In subsequent seasons, the combination of open structure from good pruning and consistent moisture from mulching will reduce the problem substantially.
Aphids
Aphids are a common spring and early summer problem on neillia, appearing as colonies of small greenfly on the soft new growth produced at the tips of the arching stems. Generalist aphid species feed on the young stems and leaf undersides, and the combination of sap removal and the chemical compounds injected during feeding causes the affected leaves to curl downward and inward at the margins. On neillia, which produces a flush of particularly soft, fast-growing shoot tips in spring, aphid colonies can establish quickly and spread across multiple stems before becoming noticeable.
The secondary signs are often what draw the eye first. Honeydew, the sticky waste product of aphid feeding, coats the leaves below the feeding site and can accumulate quickly on the characteristically arching stems where the colonies tend to settle. In warm, humid weather, sooty mould, a black fungal growth that colonises the honeydew deposits, develops on the sticky surfaces and leaves the foliage looking blackened and unhealthy. Heavy sooty mould reduces the light reaching the leaf surface and, in a severe case, compounds the stress the plant is already experiencing from the aphid feeding itself.
The encouraging aspect of aphid infestations on neillia is that they are typically self-limiting. Natural predators, particularly ladybirds and their larvae, lacewings, and parasitic wasps, establish populations in response to aphid outbreaks and usually bring them under control within a few weeks without any intervention. If the infestation is light and the plant is otherwise healthy, the most sensible approach is to leave it and allow the natural balance to reassert itself. For heavier infestations, or on plants that are already under stress from mildew or drought, direct action is worthwhile. A strong jet of water directed at the undersides of the affected shoots dislodges most of the aphids physically and washes away the honeydew deposits. Insecticidal soap spray, applied thoroughly to the undersides of all affected leaves, kills aphids on contact and breaks down quickly without persisting in the environment or harming beneficial insects that arrive after treatment. Avoid broad-spectrum insecticides, which will kill the natural predators that would otherwise regulate aphid populations.
Drought stress
Neillia prefers consistently moist, fertile soil and wilts noticeably when the ground dries out. Unlike some of its Rosaceae relatives, it does not have a reputation for drought tolerance, and plants in free-draining soil or in rain-shadow positions near walls and fences can suffer quickly during hot, dry stretches. The leaf response to drought stress is an inward curl along the length of the leaf, a slight dulling of the leaf colour, and in prolonged dry conditions an early leaf drop that leaves the arching stems bare before the season is over.
The ribbed leaves that give neillia its fine texture are a clue to its moisture needs. Deeply ribbed leaves typically indicate a plant adapted to environments with reliable rainfall, and neillia grows naturally in the moist, fertile soils of woodland and forest margins in China and Tibet. In a UK garden, the combination of a sheltered position and free-draining soil can produce dry conditions that the plant is not well equipped for.
Mulch generously at planting and annually thereafter, using compost, well-rotted leaf mould, or bark chip in a layer of five to seven centimetres around the base of the plant, keeping the mulch clear of the stems themselves. Water during dry spells, particularly in the first two to three seasons while the root system establishes. Established neillia in reasonable soil should manage most UK summers without supplementary watering, but plants in exposed or very free-draining positions will benefit from occasional deep watering during any prolonged dry period.
Other causes
Leaf spot diseases can affect neillia in warm, humid conditions, producing brown spots or lesions on the leaf surface. In heavier infections the leaves may yellow, curl at the margins, and drop. Good airflow, avoiding overhead watering, and removing affected leaves promptly are the main preventive measures. A copper-based fungicide can be applied if the problem is severe.
Coral spot fungus (Nectria cinnabarina) appears as small orange-pink pustules on dead wood and occasionally spreads into living tissue. It is an opportunist that enters through wounds or dead stems rather than attacking healthy wood directly. Cut out any affected dead wood promptly, cutting well below the visible pustules into clean tissue, and dispose of the material carefully rather than composting it. Keeping the plant vigorous through good pruning practice and consistent moisture is the most effective long-term protection.
Young neillia plants are vulnerable to slug damage near the base, particularly in spring when new growth is soft and emerging from ground level. Slugs eat irregular patches from the young leaves and can cause curling and distortion on the developing shoots. Inspect the base of the plant at night or after rain during the spring emergence period, and use biological controls or iron phosphate pellets where slug pressure is high.
Prevention and long-term care
The most important step for keeping neillia healthy is the annual post-flowering prune. Cut old flowering stems back to the base immediately after the flowers finish in June or early July. This encourages vigorous new growth from ground level, keeps the plant open and well-ventilated, and removes the wood most likely to carry powdery mildew spores into the following season. Neillia that is pruned this way stays in good shape and flowers reliably; neillia that is left unpruned becomes congested, shaded in the middle, and increasingly prone to mildew.
Plant neillia in fertile, moist but well-drained soil in a position that gets sun to partial shade. A woodland-edge situation, with morning sun and afternoon shade, suits it particularly well and most closely replicates its natural growing conditions. Avoid very exposed, windy positions, which dry the soil quickly and damage the long arching stems in strong winds, and avoid low-lying positions where water sits after rain.
Mulch generously at planting and top up the mulch annually in autumn or early spring. The mulch retains moisture, moderates soil temperature, and gradually improves soil structure over the years. Water during the first two to three growing seasons and during any prolonged dry spell in subsequent years. Beyond those basics, neillia needs very little attention and rewards good establishment care with years of reliable, graceful flowering.
Neillia pairs beautifully with irises, hardy geraniums, and other early summer perennials whose bold or frothy foliage provides a strong contrast to neillia's finely textured, arching stems. It sits naturally alongside spiraea and stephanandra in an informal mixed border or hedgerow-style planting, and its late-spring to early-summer flowering slot means it bridges the gap between spring bulbs and the main flush of summer perennials. It deserves to be much more widely grown than it currently is in UK gardens.
Frequently asked questions
Why are my neillia leaves curling?
Powdery mildew is the most common cause, producing a white powdery coating on the leaf surfaces and causing the deeply ribbed leaves to curl and distort, particularly in warm dry summers in sheltered positions. Aphids on new spring growth cause downward curling and honeydew deposits on the soft arching stems. Drought stress causes inward leaf curl and early leaf drop, as neillia prefers consistently moist soil and wilts quickly when the ground dries out.
Does neillia get powdery mildew?
Yes. As a member of the rose family (Rosaceae), neillia is susceptible to powdery mildew, and it is the most commonly seen disease on these shrubs. The white powdery coating is especially visible on the large, deeply ribbed leaves of Neillia thibetica and N. sinensis, and the curling and distortion it causes can be quite pronounced. Improving airflow around the plant, watering at the base during dry spells, and cutting out badly affected shoots after flowering all help to reduce the problem.
When should I prune neillia?
Prune neillia immediately after flowering, in June or early July. Cut the old flowering stems back to the base to encourage fresh new growth from ground level. This pruning keeps the plant vigorous and open, improves airflow through the canopy to reduce mildew risk, and ensures a good display of the long arching flower wands the following late spring. Avoid hard pruning in autumn or winter, which removes the wood that will flower next season.
Is neillia fully hardy in the UK?
Yes. Both Neillia thibetica and N. sinensis are fully hardy throughout the UK, including in northern England and Scotland. They tolerate a wide range of conditions, growing in sun to partial shade in fertile moist soil. N. thibetica holds the RHS Award of Garden Merit, which reflects its reliable garden performance across UK growing conditions.
What plants go well with neillia?
Neillia flowers in late May and June, and its long arching wands of pale pink tubular flowers combine beautifully with other early summer perennials. Irises, hardy geraniums, and Alchemilla mollis make excellent companions, with their bold or frothy foliage contrasting nicely with neillia's finely textured ribbed leaves. As a relative of spiraea and stephanandra, neillia also sits naturally alongside those shrubs in an informal mixed border or woodland-edge planting.