Kohleria is a large genus of Central and South American tropical herbs. All grow from, and produce, scaly rhizomes at their roots. Leaves are generally hairy, sometimes with attractive reddish mottling, and the flowers are usually brightly coloured, with attractive spotting.
Kohlerias are fairly adaptable plants for growing under lights, and will also do very well in a tropical greenhouse. They are somewhat more difficult for windowsill culture in most home conditions. Koellikerias will do well in the open under lights, but prefer an enclosed environment with high humidity.
It is important to remember that both genera are adapted, through their scaly rhizomes, for a period of dormancy. After some months of growth and bloom, most will begin to lose their attractive appearance -- they are preparing for dormancy, and should be allowed to dry out between light waterings. The top growth can be cut off after the leaves have mostly died.
At this point, the long scaly rhizomes can be removed from the soil ball, and divided into manageable lengths. It is not unusual for a rhizome to grow to a length of eight to twelve inches, and these can be broken into one or two inch lengths, for potting up in fresh soil.
How many are put into each pot will depend on the cultivar and the grower's intentions. Some of the leggier cultivars are grown as hanging plants, and multiple rhizomes in a plant will each produce a "crown", which will trail attractively over the edge of the pot. Other more upright cultivars can be grown with a single "crown", from a single rhizome, although multiple "crowns" can also look quite attractive.
Kohlerias may also be propagated from tip cuttings, which will root readily when taken from a plant that is growing vigorously. Some growers keep Kohlerias in constant bloom by taking tip cuttings at the peak of the plant's vigour, rooting them, and repeating the process with the new plants. Dormancy can sometimes be avoided altogether with this strategy.
When the plants are growing vigorously, it is important to provide both adequate moisture and plenty of nutrients -- Kohlerias can be heavy feeders. A constant feed method of 1/4 tsp of 60% fertilizer (e.g. 20-20-20 or 15-30-15) per gallon of water will be adequate for most plants, if watering is frequent. Slightly higher fertilizer concentrations may be desirable for some very robust cultivars.
A standard potting medium will work well, if it is well-drained as well as somewhat moisture retentive. I like to use a 2-1-1 mix (peat, perlite, vermiculite), with about 25% packaged potting soil (the kind with real dirt in it).
Good light is important, and coolish temperatures do not seem to be a barrier to good growth, and may produce stronger plants.
The Kohlerias are among my favourite gesneriads. Their spectacular flowers and pleasantly hairy leaves make for a very worthwhile and decorative horticultural subject.
Kohleria and Koellikeria were once thought to be closely related genera. However, recent phylogenetic studies have shown that they are not closely related, and all Koellikeria species have been relocated the redefined Gloxinia genus.
