Propogation from Clumping Colocasias such as Black Magic and Standard esculenta.
These grow from pups or offsets from the main rhizome. From a dry rhizome just cut the pups off with a sharp knife, allow the wound to heal over for a couple of days then place on damp perlite in a warm place to encourage the rhizome to sprout.
Black Magic rhizome clump ready to be divided
Once a sprout has started, plant in well drained, open mix of multipurpose compost with perlite and bark. These will grow better given bottom heat.
For division of already growing Colocasias allow 3 or 4 leaves to develop on the pup. Excavate some compost away from it to determine where the pup joins the main rhizome. Then cut the pup away from the main plant. Ideally there should be some roots to teese out of the compost. Pot up in multipurpose with perlite and bark.
Invariably the seperated pup will not be able to support the number and size of leaves grown while attached to the parent plant, so remove all but the youngest leaf. If no roots were present when the pup was removed, cut all leaves off, just leaving the last leaf stalk in place, and treat as per a dry rhizome.
In both cases water and feed dilute feed regularly once growth has started. Pot on as necessary until ready to plant out.
Colocasia runner node cuttings
Popagation from the runner type of Colocasia such as Burgundy Stem, Fontanesii, and Illustris
This type of Colocasia does grow some pups which should be treated as above. However, the runners do exactly that. They send out subterranean or surface runners which can travel as much as 6 feet from the plant. They then throw up a young plant. These should be left to grow 3 or 4 leaves and once rooted can be cut from the end of the runner and potted up as above. Again if there is not much root reduce the number of leaves to one until it gets going again.
Once the runner has had the terminal plant removed nothing happens for that season in the UK. However, I have found that if the runner is left on the plant over the Autumn and Winter it loses it fleshiness and becomes woody. It then has the ability to produce new plants at every leaf scale node. As the plants produce 3 to 6 runners and the runners may have 3 or more nodes. This is almost as good as tissue culture! As an experiment I have left all the runners on the plants overwinter. I just wrapped them around the inside of the pot to keep it tidy.
This winter 2006/7, as it has been more like spring, The Burgundy Stem even in the outside covered courtyard have continued to grow. The runners have been removed and cut into node sections. See above. There is one potential bud per cutting. These are laid on moist compost surface and allowed to root. The cutting in the picture right rooted in temperatures ranging from 10 to 18C. Picture taken at 3 weeks .
The sprouted cuttings need to be kept growing during the spring so avoid temperatures below 7 degrees C. Plant up in well drained compost until planted out after all danger of frost has passed.