Why Are My Arisaema Leaves Curling?

Late frost damage

Late spring frost is one of the most common causes of arisaema leaf damage in UK gardens. The bold, divided leaves emerge from a single stem in late spring and are soft and vulnerable to frost when newly unfurled. A sharp late frost in April or May can cause the leaflets to curl, brown, and collapse within hours. The distinctive spathe, which typically emerges before or with the leaves, is also frost-sensitive. However, arisaema is more resilient than it appears: if the frost was not severe enough to penetrate to the corm, the plant often produces a second flush of growth within two to three weeks.

What to do

• Cover emerging arisaema shoots and unfurling leaves with horticultural fleece when frost is forecast in April and May. The central stem is easy to protect with a fleece tent supported by stakes.
• Planting arisaema in a sheltered, dappled-shade position under deciduous trees provides natural frost mitigation, as the canopy moderates temperature swings and the overhead cover reduces radiation frost.
• Apply a generous mulch of leafmould or bark chippings over the planting area in late autumn, extending it to 10 to 15 cm deep. This insulates the corm from late frosts that penetrate the soil and delays emergence slightly, reducing frost risk to the most vulnerable tender growth.
• Do not assume a frosted arisaema is dead: wait four to six weeks for new growth to emerge before removing the plant.

Waterlogging

Waterlogging is a serious problem for arisaema. Despite preferring consistently moist soil, the corms deteriorate rapidly in persistently waterlogged, anaerobic conditions. Waterlogged arisaema corms rot over winter or in early spring, and the emerging leaf stem curls, weakens, and fails before the leaves fully unfurl. In heavy clay during a wet winter, established arisaema can be lost entirely. The distinction between the moist, humus-rich, well-drained soil that arisaema prefers and the waterlogged, airless clay that kills it is important to understand.

What to do

• Plant arisaema in well-drained but moisture-retentive soil. Incorporate generous quantities of leafmould and coarse grit into heavy clay before planting to create the ideal combination of drainage and moisture retention.
• Raise planting areas slightly to improve drainage, or install arisaema in raised beds where water drains freely while the humus-rich medium retains the moisture the plant needs through the growing season.
• In very wet gardens, grow arisaema in large containers with excellent drainage in an appropriate peat-free, moisture-retentive compost, moving them to a sheltered position in winter.

Corm rot

Fungal corm rot causes arisaema to fail to emerge in spring, or to produce a curling, yellowing leaf stem that collapses before the leaves fully expand. The corms deteriorate in wet conditions and are also vulnerable to the rot caused by physical damage during planting or lifting. A rotted corm typically feels hollow or soft and collapses when pressed. Corm rot is most likely in waterlogged soil but can also occur in bulbs stored in damp conditions or purchased already deteriorating.

What to do

• Purchase firm, plump arisaema corms and plant promptly in autumn at 10 to 15 cm depth. Inspect before planting and discard any that are soft, very lightweight, or show brown, rotted tissue.
• Dust corms with sulphur powder before planting to provide fungal protection.
• Handle corms carefully: the flatter corms of some species can look unimpressive and are sometimes planted upside down, which causes the shoot to emerge from the wrong side and curl as it struggles to reorient. Plant with the concave side facing upward or at a slight angle if unsure of orientation.

Slug damage

Slugs damage the newly emerging arisaema growth in spring, feeding on the soft, unfurling leaves and causing them to curl and develop irregular holes. The spathe and the emerging leaf stem are particularly vulnerable at the early stage before the tissues have hardened. In the damp, shaded conditions that arisaema prefers, slugs are abundant and slug damage is a consistent spring problem.

What to do

• Apply biological nematode slug control (Phasmarhabditis hermaphrodita) around arisaema plantings in spring when soil temperatures are above 5 degrees Celsius.
• Apply a ring of sharp grit around the emerging shoots to deter slug movement. This is particularly effective for the central stem before the leaves fully expand.
• Check the planting area with a torch in the evening in warm, wet spring weather and hand-collect slugs from around the plants.

Drought

Arisaema requires consistently moist soil and is not drought-tolerant. In dry conditions, the bold leaflets curl inward and the leaf stem loses its characteristic rigidity, drooping and curling as the plant attempts to reduce water loss. Drought stress is most common in arisaema planted in dry, sunny positions away from its preferred shaded, humus-rich conditions. Even in otherwise suitable shaded positions, summer drought can cause the leaves to curl if the soil dries out significantly.

What to do

• Water arisaema during dry periods through the growing season. The large divided leaves have significant transpiration rates and the plant cannot tolerate soil moisture dropping very low for extended periods.
• Maintain a consistent mulch of leafmould or bark around arisaema to retain soil moisture and keep the root zone cool.
• Ensure the planting position provides shade: shaded soil loses moisture significantly more slowly than exposed soil, and the cool microclimate reduces the plant's water demand simultaneously.

Frequently asked questions

Why are my arisaema leaves curling?

Arisaema leaves curl most often from late spring frost damage or waterlogging. The dramatic, divided leaves emerge from a central stem in late spring and are vulnerable to late frosts, which cause the leaflets to curl, brown, and collapse. Waterlogging in heavy clay causes the corms to deteriorate and the emerging leaf stem to curl and fail before fully unfurling. Both problems are common in UK gardens where spring is cold and wet.

When do arisaema emerge?

Arisaema typically emerge from mid-spring to late spring, from April to June depending on the species and the season. They are notably late to emerge compared to most spring bulbs, which can cause concern if expected and not yet visible. The late emergence is normal and is an adaptation to avoid the worst of spring frosts in their native mountain habitats. Do not dig up an arisaema that has not emerged by May: it is almost certainly still dormant underground and will appear when conditions are right.

What conditions does arisaema need?

Arisaema thrives in deep, humus-rich, consistently moist but well-drained soil in dappled shade, replicating the woodland-floor conditions of its native Himalayan and east Asian habitat. Good drainage combined with consistent moisture is the key: it needs the soil to hold moisture but never become waterlogged. Incorporate generous amounts of leafmould into the planting site. Most species are surprisingly hardy in UK conditions when planted in the right position.

Is arisaema (cobra lily) poisonous?

Yes, all parts of arisaema contain calcium oxalate crystals that cause intense burning and irritation in the mouth and throat if ingested. The corms, in particular, are highly irritating and potentially dangerous if eaten raw. The toxicity is reduced by thorough cooking, and some species are consumed as food in their native regions after extensive preparation. In UK gardens, keep arisaema away from children and pets. Wear gloves when handling corms as some people experience skin irritation from the sap.