How to Grow Arisaema (Cobra Lily or Jack in the Pulpit)

The secret to understanding how to grow Arisaema species is knowing which group your plant belongs to. Many species are excellent garden plants that will thrive for years with very little attention, while some of the rarer Himalayan species are better suited to experienced collectors.

Whether you are growing the easy and reliable Arisaema candidissimum, the spectacular A. sikokianum, or the classic North American Jack in the Pulpit (Arisaema triphyllum), the basic principles remain much the same.

Quick Growing Guide

• Botanical name: Arisaema species
• Common names: Cobra Lily, Jack in the Pulpit
• Plant type: Herbaceous perennial from a tuber
• Position: Shade to part shade, although some species tolerate or even prefer more sun
• Soil: Humus-rich, well-drained soil with plenty of organic matter
• Water: Keep moist during active growth. Most species prefer to be much drier during winter dormancy.
• Climate: Best suited to cool temperate climates, although many species grow well throughout southern Australia.
• Flowering: Spring to summer depending on species
• Height: 20 cm to over 1.2 metres depending on species
• Difficulty: Easy to moderate, depending on species.

Understanding the Different Groups of Arisaema

One reason gardeners sometimes struggle with Arisaema is that they expect every species to grow in exactly the same way. While most enjoy similar woodland conditions, there are some important differences between species.

For growing purposes, it is easiest to think of Arisaema as belonging to three broad groups: easy woodland species, intermediate species and the more demanding Himalayan and collector species.

Easy Arisaema Species for Beginners

If you are growing Arisaema for the first time, these are the species to look for. They are generally reliable, forgiving and well suited to Australian gardens provided they have good drainage and plenty of organic matter in the soil.

These include:

• Arisaema candidissimum
• Arisaema triphyllum
• Arisaema amurense
• Arisaema ringens
• Arisaema japonicum

Most of these species simply require rich woodland soil, regular moisture through spring and summer, and protection from hot afternoon sun. Once established they are long-lived plants that require very little maintenance.

Intermediate Species

These species are still relatively straightforward to grow but appreciate more consistent moisture and cooler growing conditions.

Examples include:

• Arisaema sikokianum
• Arisaema serratum
• Arisaema flavum

These species are less tolerant of drying out during the growing season and generally perform best in cool, sheltered positions with filtered light. Good drainage remains essential, particularly during winter.

Himalayan and Collector Species

Some of the larger Himalayan species are spectacular plants, producing dramatic flowers and impressive foliage, but they are also more demanding.

These include:

• Arisaema griffithii
• Arisaema speciosum
• other Himalayan species

Unlike many woodland species, some Himalayan Arisaema prefer to remain slightly moist, even during dormancy, while still requiring excellent drainage. They also appreciate cooler summers and are generally considered better suited to experienced growers or collectors.

Although they need a little more attention, they are among the most rewarding species in cultivation.

Popular Arisaema Species

With well over 100 recognised species, most originating from Asia, there is enormous variation in flower colour, foliage and size. While many are grown by specialist collectors, several species are reliable garden plants that are well worth seeking out.

Arisaema candidissimum

One of the easiest and most widely grown species, Arisaema candidissimum is often recommended for beginners. Native to the mountainous regions of China and parts of Southeast Asia, it is unusual because it tolerates considerably more sun than many woodland species.

Its fragrant pink and white striped flowers emerge in late spring and are followed by attractive foliage that remains fresh throughout summer. Given well-drained soil enriched with organic matter, it is a dependable garden performer.

Arisaema sikokianum

One of the most striking species, Arisaema sikokianum is recognised by its deep purple hood surrounding a brilliant white club-like spadix. Native to Japan, it grows naturally in cool, moist woodland.

It appreciates consistent moisture during the growing season, rich humus-filled soil and protection from hot afternoon sun. Although slightly more demanding than A. candidissimum, it is still well within the reach of most gardeners.

Arisaema triphyllum

The best-known North American species, Arisaema triphyllum is the original Jack in the Pulpit first described by botanist Thomas Nuttall in 1818.

Extremely hardy and easy to grow, it thrives in woodland gardens where it slowly forms attractive colonies. It is one of the most dependable species for cooler climates.

Arisaema ringens

A vigorous and reliable Japanese species, Arisaema ringens is grown for both its impressive flowers and handsome foliage. As with many species, there is natural variation in both flower and leaf colour, adding to its appeal for collectors.

Arisaema japonicum

Native to the cool forests of Japan, Arisaema japonicum is another excellent woodland species that enjoys moist, humus-rich soil and filtered light. It makes an attractive addition to shaded gardens.

Arisaema amurense

A compact woodland species from north-east Asia, Arisaema amurense adapts well to shaded gardens and is one of the easier species to establish. Its distinctive hooded flowers appear in spring before the attractive foliage develops.

Arisaema serratum

Commonly known in Japan as Kuzu, Arisaema serratum is found growing naturally in woodland areas throughout Japan and neighbouring parts of Asia. It is admired for its beautifully marked hooded flowers and elegant growth habit.

Arisaema griffithii

Much sought after by collectors, Arisaema griffithii is one of the most dramatic Himalayan species. Its richly coloured flowers make it a true feature plant, although it appreciates cooler conditions and careful attention to moisture, making it better suited to experienced growers.

Despite their exotic appearance, most Arisaema are surprisingly easy to grow. Once you understand the needs of your particular species, they become rewarding woodland plants that return reliably year after year with very little maintenance.

How to Grow Arisaema Species – Planting and Care

Although Arisaema look like exotic woodland plants, many species are surprisingly easy to grow. The key is providing the right conditions for the species you are growing. Most prefer a cool, humus-rich woodland environment with good drainage, but there are a few important exceptions.

Once established, Arisaema are long-lived plants that require very little maintenance and will slowly form attractive clumps.

When to Plant Arisaema

The best time to plant dormant Arisaema tubers is from late winter to early spring, just before new growth begins. This allows the tubers to establish roots before the growing season gets underway.

Container-grown plants can be planted at almost any time of year, although spring is still the ideal season as they settle in more quickly.

Planting Depth and Spacing

Plant tubers with the growing point facing upwards.

As a general guide, position the tuber around 8–12 cm below the soil surface. Smaller species can be planted a little shallower, while larger tubers appreciate being planted slightly deeper.

Space plants around 30–50 cm apart, depending on the mature size of the species. Larger Himalayan species will eventually require considerably more room than compact woodland varieties.

A generous layer of leaf mould, compost or other organic mulch helps keep the soil cool and conserves moisture during the growing season.

Soil and Light Requirements

Although Arisaema are generally regarded as woodland plants, light requirements vary between species.

Easy Woodland Species

Species such as Arisaema candidissimum, A. triphyllum, A. amurense, A. japonicum and A. ringens thrive in rich, well-drained soil with plenty of organic matter.

They prefer morning sun or filtered shade, although A. candidissimum is unusual in tolerating, and often flowering better, with considerably more sun than most other species.

Intermediate Species

Species including A. sikokianum, A. serratum and A. flavum appreciate cool, sheltered positions with filtered light and consistently moist soil during active growth. Avoid hot afternoon sun, particularly in warmer climates.

Himalayan and Collector Species

Many Himalayan species, including A. griffithii and A. speciosum, naturally grow in cool mountain woodlands where moisture is more consistent throughout the year.

These species require rich, free-draining soil and cooler growing conditions. Unlike many other Arisaema, some Himalayan species dislike becoming completely dry during dormancy and perform best if the soil remains just slightly moist over winter.

Watering Arisaema

Watering is probably the single biggest difference between species.

Most Arisaema enjoy regular moisture from spring until late summer while actively growing. The soil should remain evenly moist but never become waterlogged, as wet conditions around dormant tubers can lead to rot.

As autumn approaches and the foliage begins to yellow naturally, gradually reduce watering.

For many woodland species there is little need to water through winter. Wait until new shoots begin to emerge before watering again in spring.

The main exception is the Himalayan group, where species such as Arisaema speciosum prefer the soil to remain slightly moist, even while dormant. Good drainage is still essential.

Understanding Dormancy

One of the most common questions asked by gardeners is why their Arisaema has disappeared.

In most cases there is no need to worry.

Arisaema are deciduous perennials that naturally die back in autumn before entering winter dormancy. During this period the tuber rests beneath the soil, storing energy for the following growing season.

Do not be tempted to keep watering dormant tubers simply because there is no growth above ground. Excess moisture during winter is one of the main causes of failure with many species.

Occasionally, particularly after a hot or dry growing season, some species may remain dormant for an extra year before reappearing. This is perfectly normal and does not necessarily mean the tuber has died.

Fertilising

Arisaema are not heavy feeders, but they do appreciate fertile soil rich in organic matter.

Before planting, improve the soil with compost, leaf mould or well-rotted organic material.

In containers, a controlled-release fertiliser applied in early spring works well.

In the garden, a light mulch of compost each year together with occasional applications of a liquid fertiliser, such as worm casting tea or seaweed solution, is usually all that is required.

Avoid excessive applications of high-nitrogen fertilisers, as these encourage soft leafy growth at the expense of flowers.

How to Grow Arisaema Species in Pots

Many Arisaema grow exceptionally well in containers, making them ideal for collectors or gardeners with limited space.

Choose a deep pot with excellent drainage and use a quality potting mix enriched with compost or leaf mould. Remember that many species develop surprisingly large tubers, so they will eventually require repotting into larger containers.

Container-grown plants dry out more quickly than those growing in the garden, so regular watering during spring and summer is important. Reduce watering as plants become dormant, following the requirements of the species you are growing.

Growing in pots also makes it easier to protect valuable collector’s species from excessive summer heat or winter wet.

Propagation

Most Arisaema become larger each year and gradually produce offsets around the parent tuber.

The easiest method of propagation is to divide these offsets while the plants are dormant, from late winter to early spring, just before new growth begins. Replant immediately at the same depth as the parent plant.

Arisaema can also be grown from fresh seed, although patience is required. Seed is best sown as soon as it ripens, as germination is often improved by using fresh seed. Depending on the species, seedlings may take several years to reach flowering size, making division the quicker and more reliable method for most gardeners.

Common Pests and Diseases

One of the pleasures of growing Arisaema is that they are generally trouble-free plants. Given good drainage and suitable growing conditions, they suffer from very few pests or diseases.

Slugs and Snails

The biggest threat comes in spring when the young shoots first emerge. Slugs and snails can quickly damage new growth, particularly after rain.

Hand picking, organic snail pellets, potash or a ring of sawdust around emerging shoots can all help reduce damage. Protecting the first flush of growth usually prevents any lasting problems.

Rot

Poor drainage is the most common cause of failure with Arisaema. Tubers left sitting in cold, wet soil during winter are susceptible to rotting.

The best prevention is to plant in well-drained soil enriched with organic matter and avoid excessive watering while plants are dormant.

Dormancy or Dead?

Gardeners are sometimes concerned when an established plant fails to appear in spring. Before assuming the worst, remember that some species occasionally remain dormant for an extra season, particularly if they experienced heat or drought during the previous summer.

If the tuber remains firm when carefully examined, it will often reappear the following year.

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