Arisaemas are a genus comprising more than 200 species, commonly known as Jack-in-the-pulpits or cobra lilies. They are tuberous perennials, live for around 20 years, and are usually grown for their distinctive flowers, which usually appear in Spring or early Summer. They also have attractive dissected leaves, often shaped like an ornamental umbrella. In Autumn, they produce a densely packed cone of berries, which are a striking orange or scarlet red when ripe.
Arisaemas are members of the Araceae or Arum family, which also includes many other ornamental plants such as Zantedeschias, Spathiphyllum cochlearispathum (Peace Lilys) and Anthuriums. All members of the Araceae family have flowers borne on a spadix (a floral spike with a fleshy or succulent axis), usually accompanied by a spathe (a large bract that sometimes partially encloses the spadix). In Arisaemas, the spathe often curls over the spadix to form a hood. The spathe can be green, purple-brown or white, and is often vertically striped. In some species, the spathe or spadix elongates to form a thin tendril.
Arisaemas are found in temperate to tropical regions. The largest concentration of species is in China and Japan. There are also several species native to other parts of southern Asia, North and Central America, and Africa. Most species grow in humus-rich, well-aerated soil in open areas in woodlands, or on mountain meadows.
There are several species of Ariseama suitable for growing outside in the UK, although some may need a protective mulch over Winter in colder areas. They generally like similar conditions to Hostas and Rodgersias. Most garden soils will work fine, although good drainage is needed. Drainage can be improved by adding gravel or coarse grit when planting. Arisaemas don’t like to get too dry in Summer or too wet in Winter. Some species require a lot of water during the growing season, as they come from semi-monsoon areas. To reduce the need for watering, incorporate leaf mould in the planting hole, to make the soil more moisture-retentive. Although some species can be grown in full sun, most prefer dappled shade, especially during the middle of the day. This makes them ideal for grow in a woodland garden, or under a deciduous tree (so long as the soil is not too dry or congested by roots).Taller species should be grown in more protected areas, to minimise potential wind damage.
In nature, Arisaemas are propagated almost entirely by seed. Grown in cultivation in the UK, they will sometimes self-seed. Alternatively, the berries can be harvested (they are ripe when they turn orange or red). Each berry contains 1 – 3 seeds; they should be cleaned wearing gloves as the pulp contains germination inhibitors that irritate skin. Sow seeds indoors immediately after cleaning and cover lightly. They will usually sprout within 4 – 6 weeks. Grow on for a full season before planting out into their garden position after they turn dormant. It will usually take 2 – 4 years to have a flowering size plant, depending on the species. If plants are not setting fruit, it may be because both male and female flowers are not present, as some Arisaema species are dioecious (produce only male or female fowers). Arisaemas are unusual because plants can change from producing male flowers to producing female flowers as they mature, or may alternate each year. It can help to grow Ariseamas of different ages, or damage a larger plant to encourage it to produce male flowers. An easier way to propagate most Arisaemas is by division – simply lift the plants and remove and replant any offsets.
Species of Arisaema which are frost-hardy and suitable for growing in the UK include:
- candissimum : Notable for its pleasant fragrance. Spathes are hooded and striped white and pale pink. Grows to 30cm in height. Will tolerate full sun and drier conditions. From Western China.
- sikokianum : Flowers have a large spathe up to 20cm long, which is maroon-brown on the outside and bright white inside. The spadix is also white and club-shaped. Do not like to be grown in pots. Grow to about 40cm tall. From Japan.
- consanguineum : A taller species – typically grow to 1m tall. Stems have a snake-skin pattern, and foliage forms a striking umbrella shape above the flowers. Spathes are maroon-brown with greenish-white stripes, and form a tendril. Bulks up rapidly and is easy to grow – recommended for beginners. Will do well both in the garden and in pots, and tolerates full sun and drier conditions. From the Himalayas.
- tortuosum : The tallest of the Arisaemas, growing to 1.5m tall. Known as the whipcord cobra lily, the spadix protrudes out of the spathe and forms a vertical tendril, up to 30cm long. Both spathe and spadix are pale green, sometimes with tinges of maroon. Hardier than A. consanguineum, and fully hardy across the UK. Grow in a sheltered area for wind protection. From the Himalayas.