This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
The Gloxinia is now becoming a very popular plant, and most deservedly so; for the beautiful varieties now in cultivation have a grand and very effective appearance when in full flower. Those desirous of having a few plants in their stove collection should procure a packet of seed from some well-known grower, and from some good strain, and sow it at once in gentle heat. The seeds should be sown thinly and evenly on a fine surface, and simply dusted over with light soil, - watered with tepid water through a fine rose, covered with a piece of glass and placed in gentle heat, and never allowed to become too dry or kept too wet, as the seedlings may damp off. Whenever the plants are noticed above the soil, the glass should be removed, and a little shade afforded them when the sun is very strong. As soon as they are fit to handle the young plants should be pricked off into small thumb-pots or seed-pans, gently watered, and shaded for a few days till they take to the new soil. The soil best suited for these is an equal mixture of good fibrous peat, loam, leaf-mould, and about a sixth part of sand when the plants are small, with the addition of charcoal, bone-dust, and thoroughly decomposed cow-dung when the plants attain size and strength and require to be shifted on into larger pots.
Existing varieties should be repotted annually as soon as the bulbs begin to grow; and in doing so the old soil must be entirely removed, which can be easily accomplished if the bulbs are allowed to become rather dry. It is also advisable to put them into smaller pots, of size sufficient to allow an inch or so of fresh soil between the bulbs and the sides of the pots - this will allow of their being shifted once or twice during the summer before the flowering season. They must be shifted on whenever the roots reach the sides of the pots; and when growing freely they must be carefully watered and kept in a light, airy position near the glass without exposing them to cold draughts. A little guano-water may be given occasionally; and when the flowers begin to expand a slight shade will be necessary to prolong the flowering season as much as possible. Choice varieties can be propagated from cuttings and leaves taken off with a sharp knife and inserted in 4- or 5-inch pots in light soil, with a layer of silver sand on the surface, and covered with a bell-glass. When the flowering season is past and the growth nearly finished, stand them out in a cold frame, fully exposed to the sun, until they are thoroughly ripened and gone to rest, when they can be stored away in any place where they can be kept cool and moderately dry until wanted for potting again.