ARISAEMAS
(Araceae)
Not many gardeners in Britain are familiar with this fascinating group of plants. On the other side of the Atlantic, however, Arisaemas are definitely the new kids on the block and amongst growers of unusual exotics Arisaemas are the in-thing. Ardent American aroiders are creating new web sites devoted to their new-found passion almost every day and these are some of the best sources for those seeking Arisaema information.
So what's so special about them? Well, first of all they're not pretty (apart from one species that borders on prettiness) and they don't produce showy flowers (indeed the flowers are minute and for the most part, inconspicuous). Instead they have a modified leaf (known as a spathe) which forms a hood over the spadix (the flowering part of the plant). The well-known Arum Lily (Zantedeschia aethiopica) is a good example of this spathe-spadix inflorescence. Spathes and spadices are enormously varied in Arisaemas in terms of size, shape, colour and texture, and this, together with their leaf shape and size make them rewarding plants to grow and study. To give just one extreme example, Arisaema flavum may only grow to 10cm (4") in height with a bright yellow spathe whereas Arisaema fargesii can grow to 75cm (2'6") with a large deeply hooded spadix striped maroon or purple-red and white and produces huge glossy green, tri-lobed leaves up to 90cm (3') across.
Then there is the very interesting matter of cross-dressing or rather Arisaemas which change sex at the drop of a leaf. For those wishing to pursue this matter further or who just want to discover more about aroids in general there is a superbly detailed book by Deni Bown, Aroids, Members of the Arum Family (Timber Press, 2nd edition, 2000).
In general Arisaemas prefer to be planted in an acid to neutral soil in dappled or part shade. They make marvellous woodland plants, although some prefer a more open, sunny position. Please refer to the individual descriptions for more detailed instructions.
CULTIVATION
Since most Arisaemas originate from temperate woodlands they are naturally shade-loving plants. Of course there are exceptions to this general rule and this has been noted under the individual species, most particularly with reference to Arisaema candidissimum which can tolerate full sun in an open position. In general, almost all Arisaemas will do well in a position in dappled shade.
They prefer a rich but well drained neutral to acid soil that does not dry out in the growing season. Good old well-rotted horse manure is rich in nutrients and holds moisture well and should be incorporated with the planting soil in liberal quantities. However, if your soil is prone to waterlogging in winter the Arisaema tubers may well rot during their natural period of dormancy. To avoid this either plant the tubers in raised beds or apply plenty of grit to the planting area. The tubers can be planted to a depth of between 15-30cm (6-12inches) depending on size (they are often found fairly deep in the ground in nature).
OVERWINTERING
Most Arisaemas are frost-hardy down to -23 degrees centigrade (-10 degrees fahrenheit) but spring frosts can damage the emerging growth of A. sikokianum and A. ringens which appear fairly early in the season. The new growth can be temporarily mulched over or covered with horticultural fleece until the worst frost has passed.
For more tender species the tubers can be either dug up in mid-autumn and stored in slightly damp peat in freezer bags and placed in a refrigerator at 3-5 degrees centigrade (35-40 degrees fahrenheit) or left in the ground and heavily mulched with any insulating material to a depth of 30cm (12inches). Replant stored tubers the following spring in March or early April.
POT CULTURE
Arisaemas do best in rather deep pots, terracotta ‘long toms’ being ideal, but deep plastic pots will suffice. The tubers should be planted half-way down the pot and the pot diameter should be twice the diameter of the tuber. As Arisaemas are quite hungry plants, place a layer of well rotted manure at the bottom of the pot; the remainder of the potting mix is made up of equal parts of loam (John Innes No. 2 or 3), grit, leafmold or fibrous peat or coir compost. We place our tubers on a layer of perlite to prevent the base from rotting.
The potted tubers are kept almost dry apart from the occasional watering to prevent the pots from drying out completely. Watering is increased gradually as the new growth emerges and the plants are fed every two weeks (we use ‘Miracle Gro’). After the plant has flowered and the leaves begin to wither watering and feeding is slowly decreased until the last leaf drops off. By this time the plants are just entering dormancy and the pots are kept almost dry. This is the ideal time to repot those plants that need potting on into larger containers, to replenish compost and manure and to remove offsets to increase one’s stock.
