Arisaemas were the first Aroid I got into. Here I hope to offer a small insight into this remarkable genus.

Arisaemas were the first big aroid genus I started to collect. I remember the excitement as I looked at the remarkable structure of Arisaema triphyllum, and since then I have been developing a collection which now stands at more than 20 species!

Arisaemas (known also as 'Cobra Lilies') are a group of aroids native mainly to the middle east and over to China and Japan, but with one random offshoot in America (A. triphyllum). Most grow from tubers (except for A. rhizomatum), most die back to the ground in winter (except for A. rhizomatum) and most are reasonably hardy (except A. rhizomatum!!).

This is a tuber of Arisaema tortuosum. As you can see it is rather large, in this case about the size of a decent orange. The roots emerge from the top of the tuber, from around the growing tip (see also picture below). The tuber itself is simply a food store to supply the growth point, so the bigger the tuber the bigger the plant will be!

Arisaemas are easy to grow, but you must make sure that there is good drainage! Winter wet will rot an Ariseama, so a good trick is to rest the tuber on a 1" (2.5cm) layer of grit/perlite. Arisaemas are mainly woodland plants, but even those that grow in a sunny position in their native habitat must be planted in part shade in the UK. Many asian countries have very humid atmospheres, and it is the moisture in the air that diffuses the intense sunlight- with a drier air the sunlight in the UK is too strong for Arisaemas. Being woodland plants, Arisaemas prefer an acid soil, and don't plant tall species in a very windy spot!

If your soil does not drain well, you may want to grow Arisaemas in pots. Choose a pot which is deep (like a long-tom, but anything will do so long as it's not shallow) at least three times the width of the tuber because Arisaema tubers can put on rather a lot of weight during the growing season!

Put a crock or stone over the drainage hole and start to mix ericaceous compost with grit, or even better perlite (which is lighter so your pot won't be too heavy!). Every so often squeeze the mix in your hand- if it makes a ball, add more perlite, if it crumbles then you should be ok. The tuber wants to be planted so that the top is twice the height of the tuber in depth.....

... measure or rough guess how thick the tuber is, take the same measurement from the top of the pot, and make sure the top of the tuber is at the same level! Don't forget to take into account a layer of perlite below the tuber. Fill the rest of the pot. Don't water the plant until it is in leaf!

Ideally you should plant an Arisaema tuber in spring, just as the growth tip lengthens and the new roots start to appear as tiny bumps in a ring around the top of the tuber. In pots keep the tuber only just moist until the shoot breaks and the leaves start to emerge.

Once planted Arisaemas take little attention during the year. Both in the ground and in pots they would appreciate a high nitrogen feed, such as Chempac #2 every couple of weeks. This feeds the leaf which in turn builds up the tuber, making a bigger plant next year. If in any doubt about winter wet you can lift your Arisaemas as you would with Dahlias- just wait for them to turn yellow and for the top growth to go limp and fall over, then lift the tubers carefully and store them dry.

The easiest way to propagate Arisaemas is by division. Most species produce offsets which will detach themselves when they are ready. You will find these when you lift your tubers in autumn or repot them. Just grow them on exaclty as you grow the parent plants. Arisaemas also grow well from seed. After flowering the spathe falls away, leaving the remains of the spadix. By now each flower has become a berry, and these will swell to become the size (and shape) of a piece of sweetcorn. When they turn bright scarlet red, tap the top of the seed head (infructescence) and see if the berries fall off. If they do, collect them carefully in a small container.

NOTE: The sap in Arisaema berries contains a powerful inhibitor. This is toxic to humans; skin complaints are COMMON and long lasting. Always wear rubber gloves when handling. The fleshy berry contains an inhibitor which prevents the seed from germinating. In nature the winter rains wash away this inhibitor and allow the seeds to germinate. However, in cultivation we do not want to rely on unreliable winter rains and chance, so the seeds must be removed from the berries BUT HEED MY WARNING ABOVE!

I use a pair of tweezers and a random spiky thing I found somewhere to remove the seeds. I hold each berry, then use the spike to cut the skin and fish the seeds out. I then rub them against the kitchen towel to remove any remaining pulp.

Tools of the trade!

Store the seed dry over winter in a small envelope with the species written clearly on the front, then sow the seed in an ericacaceous compost in spring. Leave in a cold frame until germination occurs- this could be within weeks, but some species put out a root in spring and then a seed leaf in the following autumn or spring. Let them have at least one full season of growth (feed if you want to!) before splitting them up and repotting. Alternatively leave them in the garden soil and let nature take it's course!

Until recently it was a mystery to me why some of my Arisaemas freely produce seed and others won't. I've since found out that Arisaemas can be both mono and dioecious. Monoecious species have both male and female flowers on the same plant (or in Arisaemas on the same spadix), whereas dioecious species have only male or female flowers- therefore they need a member of the opposite sex to produce seed! Apparently the word 'dioecious' comes from the Greek, meaning 'two households'; a male and a female 'household' is needed to produce seed.

The monoecious Arisaemas have a little trick to keep botanists busy- plants change gender as they mature! Frequently young plants are male and mature plants are female, so if you want seed from monoecious species keep younger (flowering sized!) plants of the same species with the more mature plants. This will give you (or more accurately your plant) a better chance of cross-pollination.

I have not come across many examples of hybrid Arisaemas- they tend to appear in the wild but disappear shortly afterwards, producing no seed. However if you know where to look you may be able to find some. However Arisaemas are good at producing subspecies and forms, some of which can be extremely attractive. Of the forms, variegation has to be one of the more noticable characteristics! I have a few variegated Arisaemas (and hopefully more on the way), but the one I would really recommend to anyone collecting Arisaema must be the variegated forms of A. sikokianum.