Plant problems

Why Are My Watsonia Leaves Curling?

Q: Why are my watsonia leaves curling?

Watsonia (bugle lily) leaves curl and brown most commonly in UK cultivation because of drought stress during the spring and early summer growing season (watsonia grows from corms and produces its long, narrow, erect, sword-like leaves from late winter through spring; the leaves curl along their length and develop brown tips when the corm dries out during this active growth phase, particularly in containers or light sandy soils in a warm, sheltered position), cold damage in late winter and early spring (watsonia corms are moderately frost-tender; the young, emerging leaves that appear from late February onwards in mild UK conditions are damaged by late frosts below about -3 to -5°C, curling and turning brown or bronze at the tips and margins), or waterlogging in heavy, poorly draining UK winter soils (the corms rot in saturated conditions over winter, and the resulting weakened or rotted corm produces distorted, stunted leaves with curling and browning symptoms in spring). Watsonia is a genus of around 50 species of cormous perennials in the iris family (Iridaceae) from South Africa, primarily the Western and Eastern Cape; they are closely related to gladioli and share the characteristic fan of narrow, erect, sword-shaped leaves and upright spikes of brightly coloured, tubular flowers in shades of pink, red, orange, white, and mauve from May to July. The most commonly grown watsonia in UK gardens are Watsonia borbonica (syn. W. pyramidata), W. meriana, and numerous named cultivars and hybrids; several species and cultivars have naturalised in mild Atlantic coastal areas of Ireland, south-west England, and the Channel Islands.

Q: Is watsonia hardy in the UK?

Watsonia hardiness in the UK varies considerably by species, cultivar, and position; the most robust species (Watsonia borbonica and some named cultivars) are borderline hardy in sheltered, freely draining conditions in the mildest UK gardens, typically surviving to approximately -5 to -8°C in a well-drained, south-facing position. In the warmest UK microclimate areas (coastal Cornwall, the Isles of Scilly, coastal west Ireland, the Channel Islands, and some sheltered London gardens) watsonia has naturalised and grows and flowers reliably year after year from established corm colonies without protection. In most of England, Wales, and lowland Scotland, watsonia is best treated as a half-hardy plant grown in containers or lifted from the ground after flowering and stored frost-free from October to late March; or alternatively grown in a very sheltered, south-facing border in freely draining soil with a generous dry bark or gravel mulch from November to March to insulate the corms. The critical factor is not absolute minimum temperature but the combination of cold and wet; corms in perfectly draining, gravelly soil survive temperatures that would kill the same corms in heavy, wet clay.

Q: How do I grow watsonia in the UK?

Watsonia grows best in a warm, sunny, sheltered position in freely draining, moderately fertile, neutral to slightly acid soil; a south or south-west facing border at the base of a sheltered wall, or a raised bed with sandy or gritty loam, most closely provides the warm, free-draining conditions of the South African fynbos habitats from which the plants come. Plant corms in spring (March to April) at a depth of approximately 8 to 10 cm and 15 to 20 cm apart. In sheltered, mild UK gardens, leave corms in the ground over winter with a generous mulch of dry bark or gravel (10 to 15 cm) applied from November. In colder or wetter UK gardens, lift the corms after the foliage has died back in late summer (August to September), dry them thoroughly, and store in dry, frost-free conditions (a paper bag or open tray of dry compost in a frost-free shed or garage) from October to March. In containers, use a freely draining compost (John Innes No. 2 plus 20 to 25% coarse grit) in a 20 to 25 cm pot; water from spring growth through to autumn but keep drier in winter. Water consistently through the spring growing season and when flower spikes are developing in May and June; reduce watering from August as the foliage yellows.

Q: When does watsonia flower in the UK?

Watsonia flowers in the UK from approximately May to July in most species and cultivars; the flower spikes appear on established corms from late May and the main display runs through June into early July in most UK regions. In the very mildest UK gardens (coastal Cornwall, the Channel Islands, sheltered London) flowering on well-established naturalised colonies can begin in late April in warm springs. The flower spikes are dramatic: upright stems to 80 to 120 cm carrying a row of brightly coloured, outward-facing, tubular flowers in a one-sided spike, similar in form to a gladiolus spike but more loosely arranged and often more graceful. Flower colour varies by species and cultivar from deep pink and magenta (W. borbonica) through orange, salmon, red, white, and pale mauve (various species and hybrids). After flowering, allow the spike to set seed if required; otherwise deadhead and allow the foliage to die back naturally from August to October before lifting (in cold gardens) or mulching (in mild gardens). Watsonia grown from corms planted in spring typically flowers in its first year if the corm is of sufficient size; smaller corms may take two seasons to reach flowering size.

Watsonia (bugle lily) is a South African cormous perennial in the iris family with upright, sword-shaped leaves and elegant, one-sided spikes of brightly coloured, tubular flowers from May to July. Borderline hardy in the UK; in sheltered, mild gardens corms can be left in the ground with winter mulch, but in colder or wetter gardens they are lifted and stored frost-free. Drought stress during spring growth and late frost are the main causes of leaf curl.

Drought stress

Drought during the spring growing season is the most common cause of watsonia leaf curl in the UK; the long, narrow, sword-shaped leaves curl along their length and develop brown tips when the corm and root system dry out during active growth from February to June. Container-grown plants and those in light, sandy soils in a warm, sheltered position are most susceptible. Drought during flower spike development in May and June reduces the number and quality of flowers produced.

What to do

Water consistently from when the leaves emerge in late winter or early spring through to the end of the flowering period in late June; allow the soil to approach dryness between waterings but do not allow complete desiccation. Container plants need more frequent watering than those in the ground; check daily during warm, dry May and June weather. Reduce watering from July as the foliage begins to yellow and die back naturally. Do not water at all from August to the return of growth in late winter.

Cold damage

Late frosts in March and April damage the young, emerging watsonia leaves, which appear from late February or early March in mild UK springs; the leaf tips and margins brown, curl, and collapse after exposure to temperatures below about -3°C. In a hard late frost, the entire above-ground growth can be destroyed, though the corm usually survives to produce replacement growth if the frost is not sustained. The damage is cosmetically significant but rarely fatal unless the corm itself freezes.

What to do

Cover emerging growth with a double layer of horticultural fleece on nights when frost is forecast from February to late April; remove the fleece during the day so the leaves can photosynthesize and air circulation is maintained. In colder UK gardens, delay planting until mid-April when the risk of the severest late frosts has passed. Damaged leaves do not recover; once the risk of frost has passed, remove the worst-affected leaves and allow new growth from the corm centre to develop.

Waterlogging

Watsonia corms rot in waterlogged, poorly draining soil, particularly in the cold, wet UK winter and spring; the rotting corm produces reduced, stunted, curled leaves in spring or fails to emerge at all. The plants come from freely draining, sandy or rocky fynbos soils in South Africa and have no tolerance of sustained waterlogging. Heavy UK clay soils and low-lying, poorly draining positions are the most dangerous environments for overwintered corms.

What to do

Plant only in freely draining conditions; add grit or coarse sand to heavy soils at planting (at least one-third by volume). In poorly draining gardens, grow in containers with a very gritty compost mix, or lift corms after the foliage dies in late summer and store frost-free in dry conditions until replanting in spring. A gravel or grit collar around each corm planting position helps direct water away from the immediate root zone.

Frequently asked questions

Why are my watsonia leaves curling?

Watsonia leaves curl most commonly because of drought stress during spring growth (curl along the length with brown tips; water consistently from emergence to end of flowering in late June; container plants most at risk), late frost damage (leaf tips and margins brown after -3°C; cover with fleece on frost nights February to April), or waterlogging in wet UK winters (corm rots; grow in freely draining, gritty soil; lift and store in wet gardens). Drought in spring and cold damage are the most frequent causes in UK cultivation.

Is watsonia hardy in the UK?

Watsonia is borderline hardy in the UK; the most robust species (W. borbonica and related cultivars) tolerate approximately -5 to -8°C in freely draining, sheltered conditions. In very mild UK areas (coastal Cornwall, Channel Islands, sheltered London) corms can be left in the ground year-round with winter mulch. In most UK gardens, lift corms in late summer and store frost-free, or grow in containers moved under cover from October to late March. Cold combined with wet is more lethal than cold alone.

How do I grow watsonia in the UK?

Plant corms 8 to 10 cm deep in spring (March to April) in a warm, sunny, sheltered south-facing position in freely draining, moderately fertile soil. In mild gardens, mulch heavily from November and leave corms in the ground. In colder or wetter gardens, lift after foliage dies back (August to September), dry thoroughly, and store in frost-free conditions until March. Water consistently from emergence through flowering; reduce from July. In containers, use John Innes No. 2 plus 25% coarse grit.

When does watsonia flower in the UK?

Watsonia flowers in the UK from approximately May to July; established corms typically flower from late May with the main display through June. In the mildest UK gardens, flowering can begin in late April in warm springs. The flower spikes reach 80 to 120 cm with brightly coloured tubular flowers in pink, magenta, orange, red, or white in a one-sided spike similar to a graceful gladiolus. After flowering, deadhead or allow seed set; let the foliage die back naturally from August.