Plant problems

Why Are My Fothergilla Leaves Curling?

Q: Why are my fothergilla leaves curling?

Fothergilla leaves curl most commonly in the UK because of wrong soil pH (too alkaline for this ericaceous genus), drought stress in freely draining acid soils during summer, late spring frost damage to the young expanding leaves, or Phytophthora root rot in waterlogged conditions. Fothergilla is a genus of deciduous, ericaceous shrubs native to the moist, acid woodlands and pocosins of the eastern United States; the two species most commonly grown in UK gardens are Fothergilla major (large fothergilla or witch alder) and Fothergilla gardenii (dwarf fothergilla). Both are grown primarily for two seasons of interest: the fragrant, white, bottlebrush-like flowers produced in April and May before or with the emerging leaves; and the spectacular autumn foliage, which colours vivid red, orange, and yellow simultaneously on the same leaf, making fothergilla one of the finest deciduous shrubs for autumn colour in the UK. Like all ericaceous plants, fothergilla cannot tolerate alkaline or neutral soil; in soil with a pH above 6.0 the plant develops lime-induced chlorosis (yellowing and curling of new growth) as iron and manganese become unavailable. Drought stress is the other most common cause of leaf curl: fothergilla grows naturally in consistently moist, humus-rich woodland soils and the leaves curl, brown at the margins, and drop prematurely in dry spells.

Q: When does fothergilla flower?

Fothergilla flowers in April and May in the UK, producing dense, upright, cylindrical spikes (resembling bottlebrushes) of white stamens at the tips of the leafless or just-emerging stems; the flowers have no petals but the white stamen clusters are very ornamental and emit a strong, sweet, honey-like fragrance that is particularly noticeable on warm, still April days. Fothergilla major flowers slightly later than Fothergilla gardenii: Fothergilla gardenii begins flowering in late March or early April in mild years, while Fothergilla major typically flowers from mid-April to late May. The flowering period lasts 3 to 5 weeks depending on temperature; the flowers are attractive to early bumblebees and other pollinators. Both species' flowers emerge just as or just before the new leaves begin to expand; on some plants and in some years the flowers and young leaves appear simultaneously, while in others the flowers open on fully bare stems. The flowers are susceptible to damage from late frosts; a hard frost during the flowering period will brown the open flowers and shorten the display. Deadheading is not necessary or particularly beneficial on fothergilla, as the spent flower clusters are small and discreet; the plant's energy is better directed to the growing season's extension. The autumn colour (typically red, orange, and yellow simultaneously on single leaves) is often considered the most spectacular season of interest and lasts 3 to 5 weeks in October and November.

Q: How do I grow fothergilla in the UK?

Fothergilla thrives in acid soil (pH 4.5 to 5.5), in partial shade to full sun, in consistently moist but well-drained, humus-rich conditions. The conditions required are similar to those needed by rhododendrons, enkianthus, and leucothoe: acid soil, consistent moisture, shelter from drying winds. Plant in autumn or spring in a position with dappled or morning sun and afternoon shade, or in full sun in reliably moist soils; full sun in moist conditions can produce the most vivid autumn colour, while deep shade reduces flowering and the brilliance of autumn colour. Incorporate generous quantities of composted bark, leaf mould, or acidic compost into the planting hole; mulch annually with composted bark or pine needles to maintain soil moisture and gradual soil acidification. In hard water areas or on alkaline soils, fothergilla can be grown in large containers of ericaceous compost watered with collected rainwater; it is a slow-growing shrub and will grow happily in a container for many years. Fothergilla major eventually reaches 2 to 3 m; Fothergilla gardenii is more compact at 0.6 to 1 m and is ideal for smaller gardens. 'Mount Airy' is a particularly vigorous and reliable hybrid fothergilla (Fothergilla major x gardenii) with exceptionally vivid and consistent autumn colour; it is widely regarded as the best fothergilla for UK gardens and is available from specialist nurseries. Fothergilla needs minimal pruning: remove dead or crossing branches in spring and allow the plant to develop its natural, open, spreading habit.

Q: What is fothergilla best used for in the garden?

Fothergilla is best used as a specimen or group planting in an acid woodland garden, peat garden, or ericaceous border where it can display both its spring flowers and autumn colour to full effect; it is one of the finest deciduous shrubs for combining two distinct ornamental seasons in a single plant. In spring, the fragrant white bottlebrush flowers on bare stems are attractive from close range and suit a position where the honey-like fragrance can be appreciated near a path or seating area. In autumn, the simultaneous red, orange, and yellow colour on individual leaves is most effective when the plant is positioned where morning or afternoon sun backlights the foliage; a position on the edge of a woodland or against a dark background of evergreen hedging or conifers maximises the impact of the colour. Fothergilla combines well with other ericaceous plants that share its cultural requirements: enkianthus (for similar autumn colour in a taller, more vertical habit), leucothoe (for evergreen ground cover with complementary red winter foliage), pieris (for white spring flowers and coloured new growth), and compact Japanese maples (for additional autumn colour). In a UK garden with acid soil and dappled shade, fothergilla is one of the most reliable and trouble-free flowering shrubs available, requiring minimal maintenance beyond an annual mulch and occasional removal of dead wood.

Fothergilla (principally Fothergilla major and Fothergilla gardenii, both known as witch alder) are deciduous, ericaceous shrubs from the acid woodlands of eastern North America grown in UK gardens for their fragrant white bottlebrush flowers in April to May and exceptional simultaneous red, orange, and gold autumn foliage. Like all ericaceous plants, they require acid soil and consistent moisture; lime-induced chlorosis and drought are the most common causes of leaf curl in UK gardens.

Lime-induced chlorosis

Fothergilla is an ericaceous plant and will not tolerate alkaline or neutral soil; when soil pH rises above 6.0, iron and manganese become chemically unavailable to the plant and the new growth yellows between the veins (interveinal chlorosis), with the leaf margins curling inward as the deficiency worsens. The oldest leaves may remain relatively green while new growth is increasingly yellow and deformed; the plant grows slowly or not at all and flowers poorly. In hard water areas, even containers of ericaceous compost become progressively alkaline if watered with tap water, causing gradual chlorosis in previously healthy container-grown plants.

What to do

Test soil pH before planting; the target is 4.5 to 5.5. Lower alkaline soils with sulphur chips, composted pine bark, or acidic compost; retest after 8 to 12 weeks. In hard water areas or on alkaline soils, grow fothergilla in containers of ericaceous compost watered exclusively with collected rainwater. Apply chelated iron (sequestered iron) as a foliar feed or soil drench to a chlorotic plant as an immediate palliative measure. Do not use mushroom compost (alkaline), lime-containing fertilisers, or hard tap water.

Drought stress

Fothergilla grows naturally in the consistently moist, humus-rich, acid soils of woodland and heath in eastern North America; the plant's fibrous, shallow root system is adapted to these cool, moist conditions and is sensitive to moisture stress. In the UK, drought stress is most common in freely draining sandy acid soils during summer dry spells, in containers, or on south-facing banks exposed to full sun. Drought-stressed fothergilla leaves curl at the margins, may develop brown tips, and can drop prematurely; the autumn colour may be less intense on a plant that has been drought-stressed through summer.

What to do

Maintain a deep mulch (5 to 10 cm) of composted bark, leaf mould, or pine needles around the root zone to retain soil moisture; mulching is the most important cultural practice for fothergilla in UK gardens. Water during extended dry spells in the first two to three years; established plants in well-mulched positions rarely need supplementary watering in most UK gardens. Choose a position with some afternoon shade in lighter soils to reduce evaporation. Water container-grown plants regularly in summer using rainwater.

Late frost damage

Fothergilla is very hardy when dormant but the flowers and the young, expanding leaves in April and May can be caught by late frosts; frosted flowers turn brown overnight and the display is lost for the year. Young leaves caught by a hard frost in late spring curl, brown at the tips, and may collapse; the plant typically produces secondary growth from buds below the frost-damaged growing tips and recovers, but the season's growth can be disrupted. Fothergilla gardenii flowers slightly earlier than Fothergilla major and its flowers are therefore at greater risk from late frosts.

What to do

Avoid planting in frost pockets (hollows and low-lying areas where cold air collects on still, clear nights). A position under light tree canopy provides frost protection by slowing radiant heat loss from the plant surface. If a late frost is forecast when flowers or young growth are present, cover the plant overnight with a layer of horticultural fleece. Frost-damaged leaves and flowers do not need to be removed urgently; the plant will produce replacement growth naturally within 4 to 6 weeks.

Phytophthora root rot

Phytophthora species cause root and collar rot in a wide range of ericaceous plants, including fothergilla; the disease is promoted by waterlogged or poorly aerated soil, particularly in winter. Infected roots turn brown and mushy; the above-ground plant wilts, the leaves curl and yellow, and the plant may die rapidly in severe cases. Phytophthora infection is most likely on plants in heavy clay soils, in low-lying positions, or where irrigation or rainfall keeps the root zone perpetually saturated.

What to do

Ensure good drainage at planting; incorporate grit or coarse gravel into heavy clay soils, plant on a slight mound or bank, or choose a naturally well-draining, sloping site. Avoid waterlogging; fothergilla needs moist but aerated soil, not saturated soil. If root rot is confirmed, remove the plant, cut away all mushy roots to healthy tissue, replant in improved drainage, and withhold irrigation until new growth confirms recovery. Do not replant with ericaceous plants in the same position for several years if Phytophthora has been confirmed.

Frequently asked questions

Why are my fothergilla leaves curling?

Fothergilla leaves curl most commonly because of wrong soil pH (alkaline or neutral soil causes lime-induced interveinal chlorosis and curling of new growth), drought stress (the shallow, fibrous root system is sensitive to drying out, particularly in summer in freely draining soils), late frost damage to young spring leaves, or Phytophthora root rot in waterlogged conditions. In the correct acid, moist, sheltered conditions, fothergilla is a very reliable and trouble-free shrub requiring minimal care.

When does fothergilla flower?

Fothergilla gardenii flowers from late March to April; Fothergilla major from mid-April to late May. Both produce dense, white, fragrant bottlebrush flower spikes on bare or just-emerging stems; the honey-like fragrance is a particular feature on warm, still spring days. The flowering period lasts 3 to 5 weeks. The spectacular simultaneous red, orange, and gold autumn colour in October to November is often considered the plant's finest season.

How do I grow fothergilla in the UK?

Grow in acid soil (pH 4.5 to 5.5), in dappled to full sun, in consistently moist but well-drained humus-rich soil; mulch deeply with bark or leaf mould annually. In alkaline or hard water areas, grow in containers of ericaceous compost watered with rainwater. 'Mount Airy' is the best hybrid for reliable, vivid autumn colour. Prune minimally: remove dead or crossing branches in spring only.

What is fothergilla best used for in the garden?

Fothergilla excels as a specimen or group in an acid woodland garden, ericaceous border, or peat garden, where it offers both fragrant spring flowers and some of the most vivid autumn colour available in a UK-hardy shrub. It combines well with enkianthus, leucothoe, pieris, and compact Japanese maples. Site where morning or afternoon sun can backlight the autumn foliage, ideally against a dark evergreen background, for maximum seasonal impact.