maintained uniformly moist, but not saturated for any length of time. When the media is allowed to dry to the wilting point, growth is stunted and the plants never seem to fully recover. This is often because of root damage from concentrated soluble salts. On the other hand, saturated medium deprives the roots of oxygen. Root damage from either moisture extreme provides an opportunity for crown rot disease to develop.
In all seasons, it is a good practice to overhead water early in the morning so that the foliage drys quickly. Overhead watering can be used on African Violets up to flower opening. However, it is of utmost importance that the water be tempered close to the foliage temperature. If the water is too cold or too hot, chlorotic circles appear on the leaves, called 'ring spot'. Many greenhouses temper the water with large water heaters or heat exchangers associated with the boiler heating system. A good rule of thumb is to maintain the water temperature 8F plus or minus the air temperature. A 65 to 75F water temperature is generally safe. Once flowers begin to open, many growers use tube watering or some form of subirrigation such as capillary matting or ebb-and-flow systems, because the lifetime of the bloom is decreased by directly applying water overhead. The frequency of fertilization should be cut in half when supplied through subirrigation.
African Violets can be propagated from seed, but only a few cultivars are currently available that will come true from seed. The major means of propagation is by leaf cuttings, though some progress is being made using tissue culture.
Growers who propagate using leaf cuttings maintain an extensive stock plant program and allocate a large area to leaf and plug flats. This requires investment in greenhouse space and labor both to perform the propagation and to maintain the stock plants. Many of the cultivars better suited for commercial production are patented. Therefore, propagation should not be done without a propagators licence. The decision to propagate in-house or to order in transplants is largely an economic decision and should be made carefully.
Leaves for propagation should be selected from well maintained stock plants that are recently mature and have good green color. A good rule of thumb is a size between 1¼- to 1¾-inches long. The petiole is trimmed to ½-inch long and inserted into the medium so the leaves do not touch each other. Leaves are generally arranged in rows in 14" × 24" nursery flats at 56 to 72 leaves per flat depending on the cultivar. Many different propagation media have been used by growers including peat, peat and sand, vermiculite, peat and vermiculite, or the general potting medium.
Rooting of the leaves occurs in about two weeks and plantlets (offsets) emerge from the base of the petiole in about 6-8 weeks from sticking. At this time, the mother leaf is removed to prevent shading the newly emerged plantlets. Some growers will remove about half of the mother leaf and then remove the remainder several weeks later based on the idea that the mother leaf continues to contribute to the growth of the plantlets. Light fertilization of the young plants can begin at about the time of mother leaf removal. The total propagation time for leaf flats is 14 to 16 weeks depending on the cultivar and time of the year.
Plantlets are removed from leaf flats and separated into single crowns when they have about three to five mature leaves. They are then graded into small, medium, or large groupings. The process of grading by size may be done by hand or mechanically based on weight. Plantlets can then be rooted in plug flats (72 or 84 cells/flat), 14" × 24" nursery flats, or directly in finished pots. The latter method is often used for 2½- or 3-inch finish pots. For ease of transplanting, plug flats work best for transplanting to 4-inch pots. Once the plantlets are stuck in flats, about 6 weeks will be required to reach a transplantable size. This time can vary depending on growing condition and size grade. The small grade often requires about one week longer 