Why Are My Gunnera Leaves Curling?

Drought and water stress

Among the most moisture-demanding plants in UK cultivation; adapted to the permanently moist, humid, cloud-forest margins of Brazil; the enormous leaf surface creates an enormous transpiration rate and the plant loses water very rapidly in dry conditions. Even a brief drought causes dramatic wilting and drooping of the petioles. Recovery is rapid with rain or watering if not prolonged, but severe soil drying for several days can cause permanent leaf death.

What to do

• Position at the margin of a pond, lake, stream, or bog garden where the soil is permanently moist or near-waterlogged; this is the ideal and most effortless solution; in a conventional border, choose the wettest, most moisture-retentive position available; incorporate very large quantities of well-rotted farmyard manure or garden compost; water very heavily and regularly in dry periods from May to September; in a dry UK summer, water daily in hot weather for a fully developed gunnera; a conventional border position works best in wetter UK regions such as Wales, Scotland, south-west England, and northern England.

Cold and crown frost damage

The crown (growing point at or near the soil surface) is the most frost-vulnerable part; the leaves themselves are killed by the first hard autumn frosts, which is normal and expected. In most of England and Wales the crown survives UK winters if protected with its own dead leaves mounded over it. In cold areas of the UK, additional insulation is needed. Temperatures below approximately -5 to -8°C for prolonged periods without adequate protection can kill the crown permanently.

What to do

• After the first hard autumn frosts kill the leaves (October to November), fold the dead, dried leaf blades and stalks over the crown to create a thick insulating mound; this traditional method is very effective in mild to moderate UK winter climates. In colder UK areas, supplement with horticultural fleece, bubble wrap, or dry straw under the leaf pile. In spring, remove the protection when frost risk passes (April in mild areas, May in colder areas) and the first new leaves begin to emerge; remove no earlier to avoid exposing tender new leaves to late frost damage.

Slug and snail damage in spring

The tender, soft young emerging leaves in April and May are very attractive to slugs and snails before they have hardened and developed the characteristic rough, warty texture of mature gunnera leaves. Heavy slug damage causes ragged holes, distorted growth, and curling and collapse at the leaf edges and centres. Slug activity is worst in wet springs with mild temperatures.

What to do

• Remove the winter leaf-mound protection promptly when growth begins in spring to eliminate the shelter it provides for slugs; apply slug controls around the emerging crown in April and May: copper tape around container edges, nematode-based biological controls (Phasmarhabditis hermaphrodita, applied to moist soil in April when soil temperature is above 5°C), or iron phosphate slug pellets; checking around the crown at night with a torch and physically removing slugs is effective at a small scale; once the new leaves have hardened and developed their rough texture from about June onwards, slug damage is much less severe.

Frequently asked questions

Why are my gunnera leaves curling?

Gunnera leaves curl, droop, and petioles flag most commonly because of drought and water stress (among the most moisture-demanding UK garden plants; enormous leaf surface creates very high transpiration rate; position at pond or bog margin for permanently moist soil; heavy regular watering in dry periods May to September; in a border, incorporate very large quantities of well-rotted farmyard manure or compost; water daily in hot weather for a fully developed plant), cold and crown frost damage (leaves killed by first hard autumn frosts in October to November, which is normal; fold dead dried leaves over the crown as traditional insulating mound; supplement with fleece, bubble wrap, or straw in colder UK areas; temperatures below -5 to -8°C without protection can permanently kill the crown; remove protection in April to May when frost risk passes), or slug and snail damage on young spring leaves (tender soft emerging leaves in April to May before they harden are very attractive to slugs and snails; ragged holes and distorted curling growth; remove winter protection promptly to eliminate slug shelter; copper tape, nematode biological controls, or iron phosphate pellets in April to May; slug damage much less severe once leaves harden from June).

How do I protect gunnera in winter in the UK?

Traditional method: after first hard autumn frosts kill the leaves in October to November, cut off dead leaf stalks at or near the base leaving short stubs; fold or pile the dead dried brown leaf blades and stalks back over the crown forming a thick insulating mound of dried leaf material; the plant's own dead leaves provide excellent insulation adequate for mild to moderate UK winter climates without any additional materials. Colder areas (northern England, Scotland, exposed inland sites): supplement with horticultural fleece wrapped over the mound; bubble wrap held with netting or string; layer of dry straw or bracken under the leaf pile; temporary framework of canes or chicken wire to hold insulating material in place during winter gales; goal is to prevent crown temperature dropping below approximately -5 to -8°C for prolonged periods. Spring removal: remove protection when hard frost risk passes (April in mild areas, May in colder areas) and first new leaves begin to emerge; do not remove too early (late frost damages tender new leaves) or too late (encourages slugs under the mound).

How much water does gunnera need?

Ideal conditions: permanently wet or semi-permanently waterlogged soil at the margin of a pond, lake, stream, or bog garden; roots with continuous access to water throughout the growing season; gunnera at a pond margin with base at or just above the waterline grows most vigorously and produces the largest leaves. In a garden border: very moisture-retentive rich soil; very large quantities of well-rotted farmyard manure or compost; very regular heavy irrigation in dry spells from May to September; heavy clay soil enriched with organic matter can retain enough moisture in wetter UK regions; in drier UK regions (East Anglia, south-east) very regular heavy artificial irrigation required. Critical period: June to August when leaves are at maximum size and transpiration rate is highest; in a hot dry UK July or August a fully developed gunnera with leaves 2 m across can lose enormous quantities of water from leaves in a single day.

Is gunnera tinctoria invasive in the UK?

Gunnera tinctoria (Chilean rhubarb): listed on Schedule 9 of the Wildlife and Countryside Act 1981; illegal in England, Scotland, and Wales to plant or cause to grow in the wild; naturalised and locally invasive in Ireland (widespread and a serious invasive threat), Isles of Scilly, Cornwall, west coast Scotland, and parts of Wales and south-west England; self-seeds prolifically in moist mild western Atlantic maritime regions and can colonise stream banks, cliff tops, and wet grasslands. Gunnera manicata (Brazilian giant rhubarb): the more commonly grown species with larger more deeply lobed leaves; not currently listed on Schedule 9 in England, Scotland, or Wales; legal to grow in UK gardens; not considered invasive in the same way as G. tinctoria; responsible gardeners should prevent it from spreading to the wild. Identification: distinguishing between the two in garden plants can be difficult; purchase from reputable nurseries and verify species; particularly important for gardeners in areas where G. tinctoria is known to be invasive.