The important factors to consider, when growing African violets, are light, temperature, compost, pots, correct watering, humidity and feeding.
All plants require a good intensity of light to grow and produce flowers. The action of light upon the chlorophyll in green-leaved plants converts, by the chemical process of photosynthesis, water, carbon dioxide and fertilizers into sugar foodstuffs that the plants can use for growth. Different plant genera require different light intensities, and therefore one must consider the conditions of their original habitat to be able to provide them with light of somewhat similar intensity. Although African violets originated in East Africa close to the equator and therefore in the tropics, their natural habitat was in rocky areas near water shaded by trees and not in open, intensely sunny situations. Another point to remember is that at the equator, day and night are of equal length and so African violets require periods of light and dark during twenty-four hours. Knowing all this, we can safely say that during the summer months they require the intensity of bright diffused light, but not direct hot sunshine; in fact when exposed to the latter the foliage of the plant becomes exceedingly pale, stunted in growth, shriveled and burned, so that the plant ultimately dies. One way to assess the light intensity falling on a plant in summer is to hold one's hand between the plant and the sunlight and then to look at its shadow on the plant. If the shadow is clearly defined, the sunlight is too strong and the intensity too high, in which case the plant should be moved to another, shadier position. If the shadow of the hand can just be seen, the light intensity is just right. During the winter months, the light intensity of the sun is greatly reduced so that in northern latitudes African violets may be fully exposed to it and not be harmed in any way. In fact in these latitudes the light intensity is not sufficiently adequate nor of a long enough daily period to promote budding, and so African violets are said to rest. It is possible to increase daylight length in winter with the use of fluorescent light tubes.
Although equatorial, African violets do not require tropical temperatures since all the species have their habitats at altitudes up to 4,000ft (1,200m) and so are actually growing in cooler temperatures. The best temperature range for good growth is 65-75�F (18-24�C) during the daytime, with a night-time drop of 10�F (5�C). During the summer months, high temperatures can be a great problem and a period of four or five days at a temperature of 85�F (29�C) and over will almost certainly prove fatal to African violets. It may be helpful to increase the levels of humidity and ventilation. Then during the winter months the problem shifts to too cold a temperature: whilst an African violet will just survive a short period at 55�F (13�C) by ceasing to grow, once the temperature falls below 50�F (10�C) the plant will collapse and die. It is advisable during such cold spells to reduce watering in order to prevent damage to the roots as much as possible. In summer, open windows will provide air circulation that will normally control room temperature somewhat; it is only when excessively hot weather lasts for a week or more that African violets suffer heat exhaustion and collapse. In this situation there is very little that can be done, other than to keep the air moving by using an electric fan or air conditioning equipment. Centrally heated homes in winter give the warmth needed to keep plants in good order, provided that the heating is not tuned off overnight. However, it must be emphasized that plants should not be left on windowsills behind drawn curtains, because even if the windows are double glazed, it will still be much too cold for them overnight.
Most of the African violet species were found growing among rocks in very little soil, and this was composed mainly of humus. From this is can be understood why the root system is shallow, with hair-like roots, and why it requires an easily draining compost. Over the years many types of compost have been used, and it is for the grower to find the compost which is most suitable for growing African violets in the conditions provided. One very important fact to remember is that whatever the growing mixture, ideally its pH value should be between 6.7 and 7.0. Excessive acidity or alkalinity has a detrimental effect on the beneficial micro-organisms, or bacteria, by reducing their populations in the compost so that they cannot convert the essential nutritional elements into a form that the plant roots can absorb for growth. To avoid much of this problem, standard and large-sized show African violets should be root pruned and repotted every six months, and miniature and semi-miniature plants every three to four months.
As regards the kind of pot to use, clay or plastic pots are equally as good as each other. Once again it is left to the preference of the grower, although plastic pots are certainly easier to obtain these days. As to size of pot, African violets prefer to be slightly pot-bound at all stages of their growth and so the pot size is important. Plants should never be over-potted because excess compost causes the leaf and flower growth to slow down whilst the roots grow to fill the pot. Therefore always use the smallest pot possible for the size of the plant. For mature plants, a good guide to pot size is that the pot diameter should be one third of the diameter across the foliage of a single-crowned plant. Because African violets are not deep rooted, it is better to grow them in dwarf or half pots. It is more difficult to decide on pot diameter when growing trailing hybrids, as nowadays wide, shallow pans are often used so that the branching stems may be pinned down for a better display. In this instance it is for the grower to decide on the size of pan for the plant so that it does not appear to be either over- or under-potted. If pinning down of the stems is not wanted, always consider the type size of the trailer and choose a size of dwarf or half pot that complements the plant. Hanging baskets are currently very popular and may be used for the growing of trailing African violets, that are not intended for show, by planting several into and around a basket. However, hanging baskets tend to be too large for their ideal display, so a single plant in a hanging pot is a much better idea. These pots are available in sizes from 6in (15cm) in diameter as against 10in (25cm) diameter baskets. Also available are plastic hangers that may be attached to ordinary plastic pots of any size from 3in (7.5cm) diameter upwards, enabling small-sized plants to be displayed to advantage. It is good practice to root-prune and repot African violets at least once every twelve months; the best time of year is in the spring as the outdoor temperature begins to rise and light levels increase.
There is no mystery about how to water, the mystery is in when to water, and there is no hard and fast rule as to exactly when a plant will need to be watered. As a rule of thumb, most of the root ball should be just moist at all times to allow the very fine root hairs to carry out their function of taking in water, air and nutrients. If the compost is either waterlogged or dried out, the root system cannot carry out its proper function so the plant will wilt and die. Thus to decide when a plant should be watered, use the finger tips to feel whether the compost is moist about half an inch (1cm) below its surface. If it feels dry there, water the plant; if in doubt, do not water but wait until the following day and test again. Moistness is difficult to describe: our definition is very damp, but not wet. There are several ways of watering a plant: onto the compost from the top; into the compost from the bottom of the pot; by standing the pot on capillary matting; by a wettable wick from a reservoir.
There is another important factor associated with watering, and that is to maintain a state of humidity around the plants. Invisible water vapor produces a relative humidity, and this creates a beneficial micro-climate for African violets whereby transpiration of moisture from their leaves is lessened and the appearance of flowers and foliage is greatly enhanced. A relative humidity between 50 and 70 per cent would be advantageous, whereas below 40 per cent is too low -this will cause flowers to be sparse and small, whilst buds will go brown and drop; also the leaves will lack their normal lustre, their tips becoming brown in the low humidity. In living room conditions, low relative humidity is the normal and it must be rectified for plants to thrive. This may be done by grouping plants, standing them over water or on capillary matting, and by misting. Grouping Plants - Placing several plants together is a simple way of slightly increasing relative humidity. Each plant will help its neighbors by producing a micro-climate, and thus even less water vapor will be lost by each plant so the stomata on the leaves will close. In hot weather, however, and when central heating is needed, grouping plants does not produce a large enough increase in the humidity. A slightly higher level can be created by standing the grouped plants in bowls of moist peat; although it must be remembered to lift the plants out of the peat periodically so that their roots are prevented from growing into it. Standing over Water - Another method used to increase humidity is to stand the plants on constantly wet gravel held in trays. Care must be taken that the plant pots are not standing in the water: the rule is above the water, not in it. The water in the tray should be changed frequently, and the tray and gravel washed so that they do not become encrusted with lime scale and any small particles of compost falling from the pots. Capillary Matting - Window-sill trays holding plants may also be lined with capillary matting; this should be kept constantly moist but not wet to produce extra humidity for the plants. Again, the matting should be washed frequently to remove the excess salts left after the evaporation of water from the matting. Good contact between the pot base and matting usually means that some fine particles of compost soak into the matting, and these should also be washed out. Misting - In very hot conditions, plants may be misted twice a day using a sprayer: this should contain hand-hot but not boiling water, and it should be held about 2ft (60cm) away from and above the plants so that a fog falls on them. The sprayer action which causes the formation of miniscule droplets drastically cools the temperature of the water; this means that if the water used in the sprayer is cooler than hand hot the mist or fog falling onto the plants would be icy cold. In this event the plants would be severely chilled and brown patches on the leaves would result. Any excess moisture settled on the leaves or in the centre crown must be removed using a soft tissue, and the plants allowed to dry out of draughts or direct sunlight. The difference between misting and spraying should be appreciated. The difference is in the size of the droplets falling onto the plants. In spraying the droplets are much larger than in misting due to the sprayer being held nearer to the plants.
Sometimes the importance of feeding an indoor plant is overlooked by many people, who seem to think that a plant will grow without any help from them; they are then disappointed when it withers away and dies. It is important to understand what each nutritional element of a fertilizer will do, the major elements being nitrogen (N), phosphorus (P) and potassium (K).