 From a sales point of view, an important consideration is to provide customers with a wide variety of flower colors and cultivar selection to maintain interest. In general, cultivars are placed into flower color categories; red, blue, purple, lavender, pink, white, or bicolor. Within these color categories, 2-10 cultivars of each color may be on the production list but only one or two will be finished each week and then rotated with the next set.
Growers must consider the adaptability of cultivars to their production conditions. At some time each year, new cultivars should be ordered and evaluated for possible introduction into production based on performance under existing conditions. Recently, new introductions of different African Violet forms including miniatures and trailers have gained the attention of producers and customers. Three of the main U.S. breeder/propagators are Holtcamp greenhouses who offer the 'Optimara', 'Ballet', and 'Rhapsody' series, Arnold Fisher Greenhouses, and Nortex Nursery Industries.
African Violets are usually incompatible with other greenhouse crops because of their environmental requirements. Therefore, the grower should consider planning to use a separate greenhouse or controlled section for production. This facility should have excellent capacity for temperature, humidity, and light control.
AfricanViolets have an above average night temperature requirement. Night temperature should be 68-70F for the most rapid vegetative growth with a 75-80F day temperature. An average daily temperature of 77F provides the highest rate of leaf unfolding. When the day temperature exceeds 85F, plants often flower prematurely and grow poorly. For this reason, fan and pad cooling systems are almost mandatory in warmer areas of the country. Plant growth slows at a night temperature of 65F, and almost stops at or below 60F. Propagation areas are often maintained 2-4F warmer at night than production areas.
Bench surface heating or under-bench heating pipes are effective for increasing the growth of African Violets, particularly in the leaf flat and plug flat stages. Maintaining a medium temperature of 68F can reduce production time by two weeks and improve plant quality and flowering.
Temperature is the main factor used by growers to speed up or slow down flower development as the crop approaches finish. African Violet flower development can be divided into nine stages:
1. Bud visible in the leaf axil (2 mm long).
2. Flower stalk begins to elongate.
3. Flower stalk begins to bend.
4. Flower stalk curves over to protect primary bud.
5. Flower stalk completely curved.
6. Inflorescence pokes through leaf canopy, flower starts to straighten.
7. Flower stalk straightens out.
8. Primary flower opens.
9. Five flowers open per plant.
If the crop is not on schedule, temperatures may be raised to speed flowering or lowered to delay flowering by identifying the stage of flower development and using the temperatures in Table 1. Where possible, the temperature can be reduced a few degrees in the last week of a crop to enhance flower color and size.
|Table 1. Days from visible bud to five open flowers on African Violets.*|
|Temperature||Inflorescence Development Stage|
* Adapted from Faust and Heins, 1994.
One reason African Violets do well in most homes is because they are basically shade-adapted plants. Light intensity is the primary factor regulating both the time to flower initiation and the number of flowers produced. The usual recommendation is for 800 to 1200 foot-candles measured in the middle of a clear day. However, this depends on the temperature and season. During the winter, higher light intensities (1200 foot-candles) can be used when temperature is more controllable and the number of hours of natural light is short. In the summer, lower light intensities (800 foot-candles) are best to help control heat.
Plants receiving too much light produce hard brittle growth and are generally stunted, with short petioles and bleached foliage. Excess light can actually burn both flowers and leaves. Without enough light,