The African violet (Saintpaulia) first headed the pot-plant popularity polls about twelve years ago and has held the top spot ever since, with each year bringing an increasing number of friends.
Varieties of this gesneriad are numbered in the thousands, and it is one of the few florists’ plants which blooms throughout the year.
Natural light will vary with the season, increasing in spring, decreasing in fall. As light increases you may have to increase the shading on your greenhouse, and vice versa. I have shading on the outside of the greenhouse and two thicknesses of tobacco cloth inside.
The thickness of this cloth is not varied with the seasons, but I add or decrease shade on the outside of the house. Low light intensity reduces the number of flowers and makes for weak growth.
Even though you do not devote your entire greenhouse to African violets, you will find it profitable to reserve at least one corner for a few dozen plants. These need not be pinched to single-crown specimens. Let them grow several crowns and become covered with bloom. Such plants make wonderful gifts.
I doubt if there has ever been a pot plant for which so many soil formulas have been devised. Members of the African Violet Society never tire of coming up with new ones. For greenhouse culture, I like this formula: equal parts of loam, peatmoss, leaf mold, and sand, with a sprinkling of charcoal.
I realize, however, that not everyone has access to the leaf-mold and rotted manure commonly mentioned in soil recipes. So, with a little extra care in fertilizing, you can grow your Saintpaulias to perfection in this easy-to-make “synthetic” potting mixture: equal parts of shredded sphagnum, peat moss, and sand. Plants grown in this must receive applications of liquid fertilizer every week.
A monthly application of M teaspoonful of dried, processed, sheep manure worked into the mixture for plants in 4-inch pots will enhance their development. Use less manure for smaller pots, more for larger ones. Some growers like to mix loam, peat moss, and sand and, to a bushel of this mixture, add one 4-inch potful of superphosphate and one 6-inch potful of dried sheep manure.
Soil or synthetic mixtures should be sterilized. If you are planting in the type without loam it is unnecessary to place drainage material in the pot; with a soil mixture containing loam, drainage is a necessity. About 1/2 inch of pot chips to a 4-inch pot is ample.
Watering and Fertilizing
Always water the plants with tepid water. Leaves will be spotted when water colder than the surrounding air hits them. These whitish spots give the plants a diseased look. If you are certain that the plants growing in solid mixtures have a good root system, it is advisable to start fertilizing them about a month after potting up. If you like organic fertilizers, try one of the fish emulsions. Rapidgro, Hyponex, Plant Marvel, Blossom Booster, and others also give good results.
The size of the pot you use for your plants will depend on how you want to sell them. If you plan to sell small plants,
probably not yet in bloom, pot directly from the flat into 2-inches. Let them grow in the pots for 10 days to 2 weeks; they will be established nicely. Plants being grown for bloom will need to be shifted from the 2-inch pots to 3- and 4-inchers.
If your greenhouse is devoted exclusively to Saintpaulias, you will have to shade it: Saintpaulias do not thrive in bright sunshine. But if, like me, you grow both shade- and sun-loving plants, the placement of your African violets will require thought.
In my greenhouse, they grow mostly in flats under the top deck. Since I do not sell specimen plants but do sell leaves and seeds, I keep most of my “stock plants” growing and blooming in the flats, thus saving space, watering time, pots, and the labor of potting. In these flats of porous soil, watering is needed only once a week during the winter and twice a week in summer.
Winter temperature in my greenhouse is 72 to 75 degrees during the day, with the usual 10-degree drop at night. (Some authorities recommend a minimum of 60 at night and 70 degrees or more during the day.)
If you can’t get enough shading on your house to keep violet foliage pleasingly green, you can tack up a few layers of cheesecloth or tobacco cloth to exclude the bright sun rays. Simply string a wire across the inside of the house and another at the top of the sidewalls; then drape the material over the wires.
The late Dr. Kenneth Post, authority on florist crop production, recommended “a maximum of 1500 foot-candles of light, a minimum of 1,000” for greenhouse-grown Saintpaulias. If you are not familiar with foot-candles as a measure of light, have a friend with a photometer measure the light for you. Aim for 1200 to 1300 foot-candles during the brightest part of the day, and you’ll find your plants budding and blooming without cease.
For growth under fluorescent lights in the greenhouse, keep a distance of about 11 inches between light tubes and the larger plants’ pot rim; 4 to 6 inches for seedlings and small plants.
Thus, whatever the time of year or the occasion, if you grow African violets you will always have flowering plants to offer your customers. To you, the greenhouse owner, this constant bloom means extra money in the cash register.