Plant problems

Why Are My Asarum Leaves Curling?

Q: Why are my asarum leaves curling?

Asarum (wild ginger or birthwort) leaves curl and distort most commonly in UK gardens because of drought stress (asarum requires consistently moist, humus-rich soil and the large, glossy or matte leaves curl and go limp when the root zone dries out), slug and snail damage (the low-growing, ground-covering leaves are accessible to slugs and snails in damp conditions; feeding damage causes irregular distortion that can look like curl), or vine weevil grub damage to the roots (vine weevil larvae eat the roots of asarum in containers and in the open border, causing the plant to collapse suddenly or the leaves to curl as the root system is destroyed). Asarum is a genus of around 80 to 90 species of low-growing, ground-covering, herbaceous or semi-evergreen perennials from woodland habitats in the Northern Hemisphere, grown primarily for their attractive, often beautifully marked, kidney-shaped or heart-shaped leaves and their low, shade-tolerant, ground-covering habit. The leaves of many species (particularly Asarum europaeum, the European wild ginger) are a rich, glossy, dark green and provide a handsome, weed-suppressing, evergreen carpet under trees or shrubs where little else will grow. The plants produce small, urn-shaped, dark purple-brown flowers that are hidden beneath the foliage at ground level in spring; these flowers are pollinated by insects that crawl beneath the leaf carpet, and are rarely noticed or ornamentally significant. The foliage is the principal ornamental quality of asarum; many Asian species (particularly from Japan and Taiwan, Asarum splendens, A. magnificum, and numerous cultivars) have beautifully marked leaves with silver, white, or grey patterns on a dark green background, making them among the most decorative of all woodland ground-cover plants.

Q: Is asarum evergreen in the UK?

Asarum europaeum (European wild ginger) is generally evergreen or semi-evergreen in UK conditions; the glossy, kidney-shaped, dark green leaves persist through most UK winters, though they may be damaged or partially lost in very hard winters. The leaves are hardy and retain their appearance through mild to moderate UK winters; in a hard winter they may be damaged, turn yellow, or drop, but the plant regrows readily from the rootstock in spring. Asian asarum species (Asarum splendens, A. magnificum, and many Japanese and Chinese cultivars) are more variable in their winter hardiness and leaf retention; some are fully evergreen in mild UK winters, while others are more deciduous. The exotic, beautifully marked Asian species and cultivars are of variable hardiness in the UK; the most commonly available Japanese cultivars are typically hardy to approximately -10 to -15°C in sheltered, moist, woodland conditions, which makes them reliably perennial in most of the UK in suitable conditions, though they are not always as persistently evergreen as A. europaeum in cold winters. The deciduous North American species (Asarum canadense, Canadian wild ginger) is fully deciduous, dying back completely in autumn and regrowing in spring; it is very hardy (to -25°C or below) but provides no winter foliage interest. For year-round ground cover value, Asarum europaeum and the hardier Asian cultivars in sheltered, moist, woodland positions provide the most consistent display.

Q: How do I grow asarum in the UK?

Asarum grows best in a shaded or semi-shaded position in consistently moist, humus-rich, well-drained soil; a woodland garden, shaded border, or any position under deciduous or evergreen trees or shrubs where the soil remains moist and the light is dappled or filtered is ideal. Asarum europaeum is one of the most shade-tolerant of all ground-covering perennials and performs well even in quite deep shade under dense deciduous trees, provided the soil remains moist; dry shade is the most challenging condition and reduces the plant's vigour and leaf quality significantly. Enrich the soil with leaf mould, composted bark, or garden compost before planting; maintain an annual mulch of leaf mould to preserve moisture and replicate the moist, humus-rich woodland floor conditions the plant prefers. The plants spread slowly by rhizome to form a dense, weed-suppressing carpet over several years; individual plants spread about 20 to 30 cm per year in good conditions. Space plants 20 to 30 cm apart for ground cover; they will knit together within two to three seasons. Feed with a balanced fertiliser in spring; the plants are not heavy feeders and do not require heavy supplementary nutrition. The Asian cultivars with marked leaves are best planted in positions where the leaf markings are visible, such as at path edges in a woodland garden or in a container brought to a prominent position; the ground-level habit of the flowers means they are only visible from very close range.

Q: What is the difference between asarum and hexastylis?

Asarum and Hexastylis are closely related genera of wild ginger plants in the birthwort family (Aristolochiaceae); they were formerly all placed within Asarum and some authorities still treat them as a single genus, so the same plant may be encountered under either name in UK nurseries and garden literature. The most commonly grown North American wild gingers (Hexastylis shuttleworthii, H. arifolia, and others from the south-eastern United States) are now often placed in Hexastylis; they are evergreen, shade-loving plants with attractive, typically arrow-shaped or heart-shaped leaves that may be silver-marked, and are similar in garden use to the Asian asarum cultivars. The European wild ginger (Asarum europaeum) is universally known as asarum; the Japanese and other Asian species may be encountered as either asarum or (less commonly) under their own distinct genera. For garden purposes the distinction between asarum and hexastylis is not practically important; the cultural requirements (moist, shaded, humus-rich soil) and garden uses (shade ground cover, woodland planting, specimen display of marked foliage) are the same across the entire group. All species produce small, urn-shaped or tubular flowers at or near ground level in spring; these are botanically interesting (particularly the shapes of the perianth, which forms a tube with three lobes used to distinguish species and genera) but rarely ornamentally significant compared to the foliage.

Asarum (wild ginger) is a genus of low-growing, shade-tolerant, woodland ground-cover perennials with attractive kidney-shaped leaves; Asarum europaeum (European wild ginger) provides a glossy, dark green, evergreen carpet in deep shade, while Asian species offer beautifully silver-marked foliage. Drought stress and slug damage are the most common causes of leaf curl; consistent moisture in moist, humus-rich shade is essential.

Drought stress

Drought stress causes the large, glossy or matte leaves of asarum to curl, go limp, and lose their characteristic shine; the plants are from moist woodland floor environments and have no tolerance for dry conditions. Even brief drying out causes visible stress; prolonged drought causes leaf yellowing and drop. Dry shade under trees (particularly under shallow-rooted trees such as beech) is the most challenging UK garden condition for asarum; the combination of shade and root competition rapidly dries the soil.

What to do

Maintain consistently moist soil; mulch annually with 5 to 10 cm of leaf mould to conserve moisture and improve soil structure. Water during dry spells in summer, particularly in the first season after planting. In dry shade, improve soil moisture retention by incorporating generous quantities of leaf mould or garden compost. The plants recover quickly when watered; the curl and limpness are reversible.

Slug and snail damage

Slugs and snails feed on asarum leaves in damp conditions; feeding damage creates irregular holes, notches, and distorted edges that can cause the damaged leaves to curl and pucker. The damage is most severe in warm, wet conditions in spring (when new leaves are most vulnerable) and in autumn. The low-growing, dense habit of asarum means that slugs and snails can shelter and feed within the leaf canopy without detection; check by lifting leaves to find the undersides and soil surface beneath.

What to do

Apply a wildlife-friendly slug pellet (ferric phosphate) in spring as new growth emerges. Remove by hand in the evening or morning when slugs are most active. A grit mulch or sharp-sand barrier around individual plants deters slug movement. Avoid overwatering that keeps the soil surface permanently wet, as this encourages slug activity. Established, vigorous plants outgrow moderate slug damage; young plants and newly planted specimens need the most protection.

Vine weevil

Vine weevil larvae eat the roots and rhizomes of asarum in containers and in the border; the plants collapse suddenly or the leaves curl and yellow progressively as the root system is destroyed. Root damage is invisible until severe; by the time leaves show symptoms, the root system may already be largely consumed. Container-grown asarum is most vulnerable; the restricted root volume leaves nowhere for the larvae to escape detection.

What to do

Check the root zone of struggling container plants by carefully removing from the pot; white, C-shaped grubs in the compost confirm vine weevil. Apply a biological control (nematode drench, Steinernema kraussei, in late summer to early autumn when soil temperatures are above 5°C) to containers and border plantings. Adult vine weevils feed nocturnally on leaf margins (producing characteristic notched edges); if adult feeding is seen on leaves, treat for larvae proactively the following autumn.

Frequently asked questions

Why are my asarum leaves curling?

Asarum leaves curl most commonly because of drought stress (the plants need consistent moisture; mulch with leaf mould and water during dry spells; the curl is reversible when watered), slug damage (feeding distorts and curls new leaves; ferric phosphate pellets and hand removal in the evening; grit mulch as a barrier), or vine weevil grub damage to the roots (sudden collapse or progressive leaf curl; check the root zone for white C-shaped grubs; biological nematode control in late summer). Dry shade is the hardest UK condition to manage.

Is asarum evergreen in the UK?

Asarum europaeum is generally evergreen in mild to moderate UK winters; the glossy, dark green leaves persist through winter, making it valuable as year-round ground cover in shade. In very hard winters the leaves may be damaged or drop; the plant regrows from the rootstock in spring. Asian cultivars with marked leaves are more variable; most are evergreen in mild winters but may lose leaves in cold snaps. The North American Asarum canadense is fully deciduous.

How do I grow asarum in the UK?

Grow in shaded to semi-shaded conditions in moist, humus-rich, well-drained soil. Mulch annually with leaf mould to maintain moisture and soil structure. Space plants 20 to 30 cm apart for ground cover; they spread slowly to form a dense, weed-suppressing carpet over two to three seasons. A. europaeum tolerates deep shade; Asian cultivars prefer lightly shaded conditions where the leaf markings are visible. Protect against slugs and vine weevil.

What is the difference between asarum and hexastylis?

Many North American wild gingers formerly placed in Asarum are now classified as Hexastylis; the same plant may appear under either name in UK nurseries. For garden purposes the distinction is not practically important; cultural requirements (moist, shaded, humus-rich soil; shade ground cover) are identical across the group. Asarum europaeum (European wild ginger) is always called asarum; Japanese and Chinese species may be labelled either way.