History and MarketThe African Violet, Saintpaulia ionantha, is among the most popular of house plants with wholesale sales in 1995 exceeding 25 million dollars. This popularity is due to its ability to thrive under conditions commonly found in most homes, and its usefulness as a specimen plant, center piece, or feature in dish gardens.
Since its introduction into the United States in 1894, hundreds of African Violet cultivars have been developed that provide a wide range of flower colors, foliage types, and plant sizes. Though many Americans purchase African Violets as an impulse item, there are dedicated enthusiasts who grow, breed, and show them.
African Violets were originally discovered in 1892 in two separate locations of northeast Tanga in Eastern Africa by Baron Walter von Saint Paul, then governor of German East Africa. Saint Paul sent either plants or seed to his father in Germany where they quickly became popular in European Horticultural circles. Herman Wendlan, a prominent botanist at the Royal Botanical Gardens in Herrenhausen Germany, gave the genus name Saintpaulia in honor of its discoverer, and the two species, S. ionantha and S. confusa, became parents to most of the cultivators available today.
Most commercial growers of African Violets in this country do so on a modest scale. These growers usually obtain established transplants from a wholesale propagator for either year-round production or, more often, to meet seasonal demand. However, there are a number of large scale operations that propagate and produce upward of one million plants a year. The primary marketing holidays for African Violets are Saint Valentine's Day, Easter, and Mother's Day.
Cultivars available for greenhouse production have been selected for consistent production timing, vigorous performance in the different climatic regions of the country, trueness to type, uniform flowering, and market acceptance. 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.
African Violets have an above average night temperature requirement. Night temperature should be 68-70°F for the most rapid vegetative growth with a 75-80°F day temperature. An average daily temperature of 77°F provides the highest rate of leaf unfolding. When the day temperature exceeds 85°F, 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 65°F, and almost stops at or below 60°F. Propagation areas are often maintained 2-4°F 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 68°F 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:
- Bud visible in the leaf axil (2 mm long).
- Flower stalk begins to elongate.
- Flower stalk begins to bend.
- Flower stalk curves over to protect primary bud.
- Flower stalk completely curved.
- Inflorescence pokes through leaf canopy, flower starts to straighten.
- Flower stalk straightens out.
- Primary flower opens.
- 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 °F 1 2 3 4 5 6 7 8 9 64 50 45 40 34 29 23 18 13 0 66 48 43 38 33 27 22 17 12 0 68 46 41 36 31 26 21 16 12 0 70 44 39 34 30 25 20 15 11 0 72 42 37 33 28 24 19 14 10 0 74 39 35 30 26 22 18 13 9 0 76 37 33 28 24 20 16 12 8 0 78 34 30 27 22 19 15 11 8 0
* 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, plants have long petioles, large thin leaves, and few, if any flowers. Shading can be applied to the greenhouse glazing in March and a second application, if required, in May to reduce light intensity. This should be removed in October. The installation of an automated shade cloth system can provide a finer degree of control over light levels. Shade systems are often placed under computer control.
Growing African Violets under artificial light has been used effectively by amateurs and professionals for years. Commercial growers desiring to make more efficient use of greenhouse space have developed multi-layer bench systems in which plants on top receive natural light and those on lower layers receive fluorescent lighting. Installations for this purpose should be designed to provide 600 to 900 foot-candles with a photoperiod of 14 to 18 hours per day. This may be accomplished by mounting two, dual-bulb, 8-foot fixtures 10- to 12-inches above the plants. Lighting companies manufacture special fluorescent bulbs for growing plants, however, several studies have been unable to show that these lamps improve plant growth compared to cool-white or warm-white bulbs. Flowering of African Violets may also be improved by adding incandescent light at 10% of the total wattage. HID lighting from high-pressure sodium or metal halide lamps have also been used to grow African Violets either as a sole light source or to supplement to natural light.
The desired greenhouse humidity depends on light and temperature. African Violets usually grow well at a 50% to 70% relative humidity. During the summer, every effort should be made to keep the humidity up when temperature and light are high. Low humidity at this time can desiccate flower petal margins resulting in petal burn. Humidity may be raised by using evaporative cooling or by simply wetting walks with a hose several time a day. In the winter, high humidity, especially at night, can lead to disease problems. When the humidity approaches 100% at night, Botrytis can infect the flowers. One solution to this problem is to run a ventilating fan at night controlled by a humidity sensor.
Supplementing the greenhouse atmosphere with additional carbon dioxide to 800 to 1000 ppm increases African Violet growth and may allow plants to be grown at a lower light intensity without sacrificing quality. This technique is especially applicable during the winter months when light levels are lower and less frequent ventilation is required.
African Violets have a very fine root system and therefore require a well-aerated, well-drained medium high in organic matter. Media may be commercially available mixes or be prepared on-site. In either case, the medium should have a low soluble salts and a high water- and nutrient-holding capacity. A recommended starting media for mixing on-site would be either the Cornell A mix or the Cornell Gesneriad mix, which consists of peatmoss plus vermiculite and/or perlite. These media should be amended with dolomitic limestone to a pH of 5.8-6.2. Some growers include low rates of micronutrients and superphosphate, while others supply major and minor elements exclusively through the liquid fertilization program. Soil-borne fungal diseases can be a serious problem so many recommendations call for media pasteurization.
African Violets can be classified as light feeders, preferring a low steady supply of nutrients from a balanced fertilized. Preferably, this should be a liquid fertilizer with low salts index, high nitrate, and low ammonia and urea, such as 15-16-17 peat-lite special, 14-12-14, or 15-15-15. A constant fertilization rate of 100-125 ppm nitrogen is adequate, along with one clear watering per week. Soluble salts should be about 0.8-0.9 mmhos/cm (2:1 extract) for young plants, 1.2-1.4 mmhos/cm for plants about six weeks after potting, and no higher than 1.7 mmhos/cm at the finish. In general, newly potted plants should not receive fertilizer until the second or third week or when roots reach the side and bottom of the pot.
African Violets thrive best when the soil is 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 8°F plus or minus the air temperature. A 65° to 75°F 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 to mature in the plug flat and the large grade about one week less than the medium grade.
The majority of African Violets are potted and finished in 4-inch pots, though 4½- and 5-inch pots are not uncommon. During potting, care should be taken not to plant the plugs too deep and that patented cultivars are properly labeled. Once potted, the plants can be maintained on the bench, pot-to-pot, for 5 to 6 weeks. Optimum light, temperature, and other cultural practices are important at this stage for a vigorous uniform crop. When flower buds begin to poke up through the leaf canopy, plants can be placed at a final spacing of four pots per square foot on capillary or ebb-and-flow benches. African Violets are usually shipped when 5 blooms are open depending on the desire of the market. This will usually occur 5 to 6 weeks after spacing. The total production time from leaf cutting to a finished 4-inch pot is 32 to 36 weeks depending on the time of year and geographic location.
The schedule in Figure 1 is a generalization. Individual stages may require more or less time depending on the cultivar, time of the year, and geographic location.
Figure 1. Production stages and timing for scheduling African Violets in 4-inch pots.
The most important consideration for a disease-free crop lies with sanitation of all pots, flats, benches, medium, and any other articles coming in contact with the plants. General greenhouse cleanliness is a must! This is especially true where "crown rot" (Pythium/ Phytophthora) is concerned. Other factors in disease prevention are: obtaining healthy transplants, keeping plants growing vigorously, the correct environment, and carrying-out production stages on time. Fungicide treatments come and go, but it is easier and less expensive to prevent disease problems rather than cure them. Powdery mildew can be a problem during changeable weather. This can be controlled by burning sulfur and modifying the environment to keep the foliage dry. Botrytis is best controlled by reducing the humidity.
Crown and Root Rot
One of the most serious fungal problems of African violet is usually first noticed when the crown and roots of the plant turn soft and mushy. The older leaves droop, and the younger leaves in the center of the plant appear stunted, turn black and die. The fungi Pythium species and Phytophthora species can cause this problem, especially when plants are watered excessively, have poor drainage, or are planted too deeply. Any of these conditions can contribute to rotting of the crown and roots.
Prevention and control: Prevent disease by always using sterilized potting soil mixes and clean containers when planting. Do not plant African violets too deep. Discard severely affected plants.
Botrytis blight is caused by the fungus Botrytis cinerea and often first appears as small water-soaked lesions on the underside of the leaf. Leaves, stems or flowers appear blighted and turn dark brown to gray, often with a fuzzy coating on the surface.
Prevention and control: Collect and discard all dead and dying plant material. Provide better air circulation, and avoid getting the flowers and foliage wet. Botrytis often follows mite injury, so controlling these pests aids in controlling this disease. Remove and discard infected leaves and flowers. Keep leaves and flowers dry when watering plants. Provide better air circulation around plants.
Pests attacking African violets may be divided into three groups according to the damage they cause. These groups are chewing pest, sucking pests and nuisance pests. Damage from chewing pests usually occurs rapidly and is evident immediately. These pests should be eliminated as soon as they are detected. Symptoms of chewing pests include wilting of plant (root or crown damage, severed leaves or flower buds, holes in leaves or flower petals and discolored areas on the surface or margins of leaves or flower petals.
Sucking pests insert their mouthparts into plant tissue and suck out the juices. Some inject toxic compounds into the plant and some are capable of transmitting certain plant diseases. The symptoms of sucking pests often go unnoticed for a period of time. This allows the pests to become established and increase in numbers, resulting in considerable plant damage. The symptoms of sucking pests are wilted appearance, presence of honeydew, curling or stunting of leaves, discoloration (yellowing) of leaves and necrotic (dead tissue) spots in leaves.
Nuisance pests cause no damage. They are considered pests simply because their presence is not desirable. Such insects flying or hopping about detract from a beautiful centerpiece or a specimen plant on exhibition. Some nuisance pests multiply rapidly and often are found in overwhelming numbers. Such infestations are easily eliminated with careful management and properly selected insecticides. Greenhouse cleanliness and isolation of new incoming material can go a long way toward preventing insect problems.
Mites are a very serious pest problem on African Violets. Mites are not true insects, but closely related to spiders. They are unable to been seen by the naked eye, they are only detectable by the leaf damage. The damage is first seen on the new growth (in the center of the plant) and includes stunting of new leaves, leaf curl, and grayish appearance. Flower buds may also become stunted, fall out, or become misshapen. Cyclamen mites like high humidity (80 to 90 percent) and temperatures around 61°F. They hid in the crown of the plant and leaf folds to avoid light. Mites feed by sucking on the plant nutrients. They also inject a toxin into the plant while feeding that disrupts the plants growth. Heavy infestations cause leaf drop and even death.
Prevention and control: Plants should be well spaced to prevent the mites from spreading. Any tools or watering can that touch the infected plants should be sterilized before bing used on non-infected plants. Heavily infected plants should be discarded along with the pot they inhabit or soaked in a 1:9 bleach/water solution for thirty minutes.
Two forms of mealybugs are a major problem on African Violets. They include the Comstock mealybug (Planococcus citri) and the citrus mealybug (Pseudococcus comstocki). The insects are 1/4 inch in length. Their bodies are soft with a waxy white coating that appears cottony. They can be found on the stems, leaves, and leaf crotches. Mealybugs feed by sucking the sap from leaves which causes distortion and stunting. They also excrete a stinky sap called honeydew hat attracts ants and can form sooty mold. Heavy infestations can cause death of leaves or the entire plant.
Prevention and control: Inspect all new plants for mealybugs before placing them with existing plants. Check all surface, including the pot bottom for mealybug eggs. For light infestations, removal with an alcohol soaked cotton ball or cloth. Heavy infestations are hard to control due to a thick waxy coating that covers their bodies. They must be treated in the nymph stage two to three times weekly.
At least 2, and possibly 4, species of soil mealybugs infest African violets. The most common species is the Pritchard mealybug, which is about 1/40-inch long and milk-white in color. The white color comes from a powdery, waxy material secreted by the mealybug which covers its body. These pests resemble tiny bits of perlite in the plant root-ball. Infestations of soil mealybugs may go unnoticed for long periods of time. If infested plants are put under stress from lack of water, fertilizer or temperature, symptoms develop rapidly. Mealybugs destroy the root hairs and symptoms of infestation include yellowing plant leaves, wilted appearance, stunting and bloom reduction.
Prevention and control: Treat soil mealybugs as soon as an infestation is detected. A drench will give better results than a foliar or soil surface application.
Spider mites, often called "red spiders", are small and red. They barely can be seen with the unaided eye. Seldom do these mites attack violets, but when they do, damage is severe. Damage appears as bleached out or yellowish spots on the leaves. Spider mites most often move to violets from other ornamentals such as marigolds, ivy or mums.
Aphids are small, soft bodied insects. Some may have wings. They may be yellow, green or black. They damage plants by sucking juice from leaves and stems. Aphids secrete honeydew and heavy infestations may result in the sticky substance covering the plant. Aphids reproduce rapidly so infestations should not be neglected.
Prevention and control: Apply an insecticide as soon as aphids are found.
Scale insects are very small, soft bodied pests that attach themselves to plant leaves and petioles. They secrete a covering or "scale" over their body. Once attached, they never move. Several species of scale insects have been found on African violets. Scale, like aphids, secrete honeydew which collects on the plant.
Prevention and control: Inspect plants having honeydew or a wilted appearance for the presence of scale. Control often may be achieved simply by removing the attached scale insects from the plant. Treat heavy infestations with an effective insecticide.
The American cockroach is the most commonly reported chewing pest of African violets. Both immature and adult cockroaches damage violets. They usually eat on flower buds and blossoms, but they also feed on leaves and leaf petioles. Roaches occasionally cause extensive damage to rooting leaves and seedlings.
Thrips are very small, thin winged insects that feed on the flowers and leaves. Injury is characterized by irregular silver streaking with small black excrement dots on the infected surfaces. Thrips are often found on the flowers where they cause stunting, distortion, discoloration or streaking, and shortened flower lifespan.
Prevention and control: Thrips can be controlled with repeated applications of many insecticides.
Foliage Feeding Larvae
Many species of foliage feeding larvae have been observed on African violets. The most common include the salt marsh caterpillar, various loopers and armyworms. In most instances these are accidental pests that have found their way into homes or greenhouses. They attack violets because a more suitable host plant is lacking. These larvae are voracious feeders and only a few can cause severe damage.
Prevention and control: Control often can be achieved by picking the larvae from the plants and destroying them.
Foliage Feeding Beetles
Beetles are not common pests of African violets; however, several species feed on the plant. These include the twelve-spotted cucumber beetle, banded cucumber beetle, green june beetle and several species of flea beetles. Beetles are more mobile than foliage feeding larvae and they may cause severe damage in a violet culture if not detected and eliminated quickly.
Snails and Slugs
Snails and slugs are predominantly greenhouse pests. They prefer to feed on very tender tissue and occasionally damage rooting leaves and small seedlings. These pests generally feed at night and hide beneath pots, flats and other objects during the day. Both snails and slugs leave a slime trail behind them as they travel about. Treatment for snails and slugs should be applied when their presence is detected. Bait formulations are very effective in controlling these pests.
Symphylids are about 1/4-inch long. They are milk-white in color, elongate and have 12 legs. They have long antennae and no eyes. These pests are subterranean in habit and are seldom seen on the soil surface. They prefer moist soil that is high in organic matter. Heaviest populations of symphylids occur in the fall and winter. They are very active, but are hard to find unless present in large numbers. Symphylids seldom cause damage to plants and are usually just a nuisance, but a few species will feed on tender roots of seedlings.
Broad mites resemble cyclamen mites but are only occasional pests of violets. Unlike cyclamen mites, they do not attack the center of the plant, but prefer the older, bottom leaves. They feed on both the upper and lower surface of the leaves; damaged leaves turn yellowish and the edges may curl under.
Full grown pillbugs are about 3/8-inch long and gray in color. Although they are capable of damaging seedlings, they are most often considered a nuisance pest. They feed on decaying organic matter and are found in moist soil and debris on the soil surface. Pillbugs often enter potted plants through drain holes and push soil out the hole, leaving a mess to be cleaned up.
Earwigs are dark brown to black insects. They are elongate and have pincer-like structures on the end of their abdomen. Full grown earwigs are about 3/4-inch long. These insects feed on decaying organic matter, but some occasionally feed on living plant tissue. Earwigs frequent dark, moist area and thrive in potted plants. They are frequently found on benches or shelves beneath pots.
Springtails are minute, wingless insects about 1/10-inch long and vary in color from black to gray to white. They are found in dark, damp areas and in soils high in organic matter. Some species occasionally feed on living plant tissue such as sprouting seed, roots and tender shoots. Large concentrations of springtails often are found floating in water reservoirs or on the soil surface. They are very mobile and can be found crawling on plants, pots and tables. Literally thousands may be found in sand, gravel or other materials in propagation beds or plant trays.
Prevention and control: Control springtails by treating benches, shelves or the soil beneath greenhouse benches. Insecticide may need to be applied to the outside of pots and saucers and to the soil surface of potted plants when heavy infestations occur.
Early pest detection and control are essential to prevent damage. Inspect plants frequently and treat insect infestations as soon as they are detected. Thoroughly examine newly acquired plants and isolate them for a period of time before they are introduced into a culture. Before using a pesticide, read the label thoroughly and apply the pesticide only as directed on the label.
Before purchasing and using a pesticide, check the product label. Solvents, carriers, concentrations and other factors may differ with products even though the active ingredient is the same. Be sure a product is registered for use on African violets and for the specific pest you wish to control before you use it.
Failure to Flower
African violet flower buds may fail to open, turn brown and fall off. Unfavorable environmental conditions such as low temperatures, poor soil aeration, wet soil or excessively dry air contribute to flower failure. Blossoms will drop if there is the slightest presence of cooking gas.
The symptom of petiole rot is a rust-colored spot that appears where the stem of the leaf touches the pot. This is not a disease but is caused when fertilizer salts accumulate on the rim of the pot and the soil surface. Avoid over-fertilization of plants, and be sure to use a salt-free source for watering, such as, rainwater. Tape on the rim of the pot will prevent this problem. Leach out the remaining salts in the soil, by flushing the container with plenty of fresh water.
http://aggie-horticulture.tamu.edu/violet/insects/insects.html (Cole). http://hgic.clemson.edu/factsheets/HGIC2250.htm (Scott) http://www.ianr.unl.edu/pubs/horticulture/g182htm