Plant problems

Why Are My Enkianthus Leaves Curling?

Q: Why are my enkianthus leaves curling?

Enkianthus leaves curl most commonly in the UK because of wrong soil pH (too alkaline), drought stress in free-draining acidic soils, late spring frost damage to young growth, or vine weevil attacking the roots. Enkianthus is a genus of deciduous, ericaceous (lime-hating) shrubs from Japan and the Himalayas; the most widely grown in UK gardens is Enkianthus campanulatus (redvein enkianthus), a graceful, upright deciduous shrub with clusters of small, pendulous, cream to pale yellow bell-shaped flowers with red veining produced in May and June, and spectacular scarlet, orange, and gold autumn foliage. Like all ericaceous plants (rhododendron, camellia, pieris, blueberry), enkianthus requires acid soil with a pH below 6.0, ideally 4.5 to 5.5; in alkaline or neutral soils the plant cannot take up iron and manganese from the soil, and the resulting lime-induced chlorosis (iron deficiency) causes the young leaves to yellow between the veins, with the leaf margins curling inward as the deficiency progresses. Drought stress on enkianthus planted in freely draining or sandy acid soils causes the leaf margins to curl and brown; enkianthus, despite its woodland origin, needs a consistently moist but well-drained soil and is not as drought-tolerant as some other ericaceous shrubs. Late frost damage to the young growth in April or May causes the expanding leaves to curl, brown at the tips, and may cause whole young shoots to collapse; the plant is very hardy when dormant but the new spring growth is vulnerable to late frost. Vine weevil larvae feed on the roots and can cause sudden wilting of individual shoots.

Q: When does enkianthus flower?

Enkianthus campanulatus (redvein enkianthus) flowers in May and June in the UK, just before or alongside the first flush of new leaf growth; the clusters of small, pendulous, bell-shaped flowers appear in terminal clusters at the ends of the previous year's shoots and are individually small but collectively very ornamental at close quarters. The flowers are cream to pale yellow with distinctive red or dark pink veining, giving the plant its common name of redvein enkianthus; different forms and selections vary in the depth and colour of the veining, from lightly flushed cream to deep rose-pink (as in the selection 'Red Bells'). The flowering period is typically 3 to 4 weeks; the individual bells are delicate and are susceptible to damage from late frost or heavy rain, which can shorten the display. Enkianthus perulatus (white enkianthus) flowers slightly earlier in April to May with pure white bell flowers; it is a more compact plant than Enkianthus campanulatus with outstanding scarlet autumn colour. Both species' flowers are attractive to bees (the pendant bells are visited by bumblebees and honeybees) and are followed by small, five-parted capsular fruits that are not ornamental but provide seed for propagation. The autumn colour of Enkianthus campanulatus is the plant's main display season in most UK gardens; well-established plants in acidic woodland or peat garden conditions develop brilliant scarlet, orange, and gold foliage that rivals Japanese maples for intensity, lasting for 3 to 5 weeks in October and November before the leaves fall.

Q: How do I grow enkianthus in the UK?

Enkianthus campanulatus requires acid soil, partial shade or dappled sunlight, and consistently moist but well-drained conditions to thrive in the UK. The key requirements are: acid soil with a pH of 4.5 to 5.5 (test your soil before planting; enkianthus cannot be grown successfully in alkaline or neutral soils without major remedial work); partial shade or dappled sunlight (the plant grows naturally at the edges of woodland and benefits from shelter from strong, drying afternoon sun, which can scorch the thin leaves and stress the shallow root system); moisture-retentive but well-drained soil (enkianthus needs consistent moisture but will not tolerate waterlogging; the ideal soil is a leafy, humus-rich acid soil similar to the conditions under Japanese maples and rhododendrons); and a sheltered position that reduces the risk of late frost damage to spring growth. Prepare the planting position by incorporating generous quantities of composted bark, leaf mould, or acidic compost into the soil; mulch the root zone each spring with composted bark or pine needles to maintain moisture, suppress weeds, and gradually improve soil acidity. In hard water areas where soil pH is high, enkianthus can be grown in containers of ericaceous compost watered with collected rainwater; use a deep container with good drainage and repot every 2 to 3 years as the plant grows. Do not plant in full sun in dry positions; the thin-textured leaves of enkianthus are prone to scorch and moisture stress. Enkianthus needs minimal pruning; remove dead, damaged, or crossing branches in early spring and thin any overcrowded growth to maintain an open, vase-shaped habit.

Q: What is the best enkianthus for autumn colour?

Enkianthus campanulatus is generally considered the best species for outstanding autumn colour in UK garden conditions: well-established plants in acid woodland or peat garden settings develop brilliant scarlet, orange, and gold foliage in October and November that can rival Japanese maples for intensity and duration. Within the species, the form 'Campanulatus' is the most widely available and reliable; the selection 'Red Bells' has deeper-coloured flowers and consistently good autumn colour. Enkianthus perulatus (white enkianthus) is a more compact, earlier-flowering species that produces perhaps the most intense scarlet autumn colour of any enkianthus, though the display may be shorter than that of Enkianthus campanulatus; it is ideal for small gardens where space is limited. Enkianthus cernuus f. rubens is a distinctive compact form with deep red flowers and very good autumn colour; it is less common in UK nurseries than the other species but worth seeking out. Enkianthus deflexus is a large, vigorous species with cream flowers and strong autumn colour; it can make a substantial woodland shrub or small tree in favourable conditions. All enkianthus species and forms produce their best autumn colour in acid soil conditions; in less ideal (but still acidic) soil, the autumn colour may be less intense or shorter-lived. A position in dappled shade rather than full sun tends to produce longer-lasting, more saturated autumn colour; full sun can bleach the colours and shorten the display.

Enkianthus campanulatus (redvein enkianthus) is a graceful, deciduous, ericaceous shrub from Japan grown in UK acid gardens for its delicate pendant bell flowers in May to June and spectacular scarlet-orange autumn foliage. It belongs in the same acid soil group as rhododendrons, camellias, and blueberries; like them, it curls and yellows when the soil pH is wrong, when drought stresses the shallow root system, or when late spring frosts catch the opening leaves.

Lime-induced chlorosis

Lime-induced chlorosis is the most serious and common cause of leaf problems on enkianthus in UK gardens. When soil pH rises above 6.0, iron and manganese become chemically locked and unavailable to ericaceous plants; the young leaves yellow between the veins while the veins themselves remain green (interveinal chlorosis), and as the deficiency progresses the leaves curl inward, develop brown margins, and may drop prematurely. The plant flowers poorly and grows weakly. This problem is permanent unless the underlying soil pH is corrected; short-term applications of chelated iron (sequestered iron) can temporarily improve leaf colour but do not address the root cause.

What to do

Test the soil pH before planting enkianthus; the target range is 4.5 to 5.5. If the pH is above 6.0, acidify the soil by incorporating composted pine bark, sulphur chips (elemental sulphur), or acidic compost; retest after 8 to 12 weeks and repeat if necessary. On alkaline soils or in hard water areas, grow enkianthus in large containers of ericaceous compost and water with collected rainwater. Apply chelated iron as a foliar feed or soil drench to a chlorotic plant as an immediate measure while the soil pH is being corrected. Once established in the correct soil, enkianthus is very reliable and trouble-free.

Drought stress

Enkianthus grows naturally in moist, humus-rich woodland soils in Japan and the Himalayas; the thin-textured leaves are not adapted to dry conditions and curl and brown at the margins when the root zone dries out. Drought stress is most likely in freely draining acid soils (sandy heathland soils, for example) during extended dry spells in summer, in container-grown specimens, and in newly planted specimens in their first two seasons before a deep root system has developed. The shallow, fibrous root system of enkianthus (similar to rhododendrons) makes it particularly sensitive to drying out at the surface.

What to do

Maintain a deep mulch (5 to 10 cm) of composted bark, pine needles, or leaf mould around the root zone throughout the year; mulching is the single most effective way to maintain the consistent moisture that enkianthus needs. Water during dry spells in the first two seasons; established plants in well-prepared, mulched soil rarely need irrigation. Water container-grown plants regularly in summer using rainwater; allow the compost surface to begin drying before watering but do not allow the root ball to dry out completely. A position in dappled shade rather than full sun reduces moisture stress.

Late frost damage

Enkianthus campanulatus is very hardy when dormant (surviving to -20°C or lower in its Japanese homeland), but the young spring growth that emerges in April and May is tender and can be caught by late frosts at temperatures below -2 to -3°C. Frost-damaged young leaves turn brown and curl, and may fail to expand; affected shoots look dead at the tips and can give the plant an untidy appearance in late spring. The plant typically recovers by producing secondary growth from buds below the frost-damaged tips; this new growth flushes out in May or June and restores the plant's appearance, though the secondary growth may be less vigorous than the primary spring flush.

What to do

Avoid planting enkianthus in frost pockets (low-lying areas or enclosed hollows where cold air collects on still nights). A position with overhead canopy cover (under deciduous trees, for example) provides several degrees of frost protection by reducing radiant heat loss from the leaf surface. If a late frost is forecast when enkianthus is in active growth, cover with horticultural fleece overnight. Once the risk of frost is past, cut back frost-damaged shoot tips to healthy, undamaged buds to encourage replacement growth.

Vine weevil

Vine weevil (Otiorhynchus sulcatus) larvae feed on the roots of ericaceous plants including enkianthus; root damage causes individual shoots to wilt and collapse, particularly in summer when larvae are large. The first sign above ground is often a shoot wilting despite adequate soil moisture; digging around the root zone will reveal C-shaped cream larvae in the surrounding soil. Adult vine weevils notch the leaf margins with characteristic curved cuts at night in summer; this leaf notching, though unsightly, is less damaging than larval root feeding.

What to do

Apply the biological control nematode Steinernema kraussei to the moist soil around the plant in August to September when soil temperatures are still above 5°C; the nematodes parasitise and kill vine weevil larvae before they cause serious root damage. Repeat in spring if the problem persists. In containers, repot any plant showing wilt symptoms; remove and destroy all larvae found in the compost. Mulching with a coarse bark mulch deters adult weevils from laying eggs in the soil.

Frequently asked questions

Why are my enkianthus leaves curling?

Enkianthus leaves curl most commonly because of wrong soil pH (alkaline or neutral soil causes lime-induced chlorosis and interveinal yellowing with curling margins), drought stress (the thin leaves curl and brown at the margins when the shallow roots dry out), late frost damage to young spring growth, or vine weevil larvae in the root zone. Enkianthus is a trouble-free plant in the correct acid, moist, woodland-edge conditions; most problems trace back to unsuitable soil pH or moisture conditions.

When does enkianthus flower?

Enkianthus campanulatus flowers in May to June with clusters of small, pendant, cream to pale yellow bell-shaped flowers with red veining; the display typically lasts 3 to 4 weeks. 'Red Bells' has deeper coloured flowers. Enkianthus perulatus flowers slightly earlier with pure white bells. The autumn colour (scarlet, orange, gold in October to November) is the main ornamental season for most UK garden specimens.

How do I grow enkianthus in the UK?

Grow in acid soil (pH 4.5 to 5.5), in dappled shade or partial sun, in moist but well-drained humus-rich conditions; maintain a deep mulch of bark or leaf mould around the root zone. In hard water areas or alkaline gardens, grow in containers of ericaceous compost watered with rainwater. Prune minimally: remove dead or crossing branches in early spring only. Enkianthus is slow-growing but very long-lived in the right conditions.

What is the best enkianthus for autumn colour?

Enkianthus campanulatus is the most widely available and reliable for autumn colour in UK gardens, turning brilliant scarlet, orange, and gold in October. The form 'Red Bells' has deeper flowers. Enkianthus perulatus is more compact with very intense scarlet autumn colour, ideal for smaller gardens. All enkianthus species produce their best colour in acid soil with some shade; full sun can bleach the colours and shorten the display.