QI repotted a nice African violet in July and it hasn't bloomed since then. What do I need to do to get it to bloom?
AAfrican violets are tropical houseplants that are prized because they produce beautiful flowers almost constantly throughout the year. African violets are fairly easy to grow, but you must meet their particular requirements to keep them in bloom. A problem with any one of these requirements can cause a lack of flower production.
First, check the light level that your plant is receiving. African violets like bright but indirect light. North or east windows are usually best, but violets can also be grown in south windows as long as the sunlight is filtered through a sheer curtain. If the plant's leaves are stretching upwards instead of horizontally it indicates insufficient light.
African violets also grow and bloom very well under fluorescent lights. The lights should be suspended about 10 to 12 inches above the plant and should be on for about 12 hours a day. (Use an automatic timer so you don't have to remember to turn the lights on and off.)
African violets like a consistent temperature of about 72 degrees. Plants should be within 12 inches of a window to get sufficient light, but during winter it can be too cold that close to a window. You may want to put the plants under fluorescent lights in a warmer part of the house for winter. African violets also like humidity, so you may want to use a room humidifier or set the pots in trays filled with pebbles and water (make sure the water line is below the tops of the pebbles).
Using diluted fertilizer
African violets like evenly moist but well-drained soil. Water weekly, using a diluted fertilizer. Look for fertilizer labeled specifically for African violets. When you water, avoid wetting the leaves. To do that, either water very carefully from the top of the pot, or try watering from the bottom. This means putting room-temperature water in a plant saucer, then setting the pot in the saucer and letting the water absorb upwards into the pot. Check the plants after 10 to 15 minutes; when the top of the soil looks moist take the pot out of the saucer and let it drain thoroughly. Dump any excess water out of the saucer before setting the pot back into it.
Because African violet roots need plenty of air, the plants will not thrive in overly heavy soil. Many bagged potting soil mixes contain too much fine, black muck peat, which is not sufficiently aerated and can compact. Look for a soilless potting mix that is composed primarily of sphagnum peat moss, perlite and vermiculite. When repotting, don't pack the potting mix too tightly.
African violets like to be in somewhat cramped pots. Use shallow pots, not more than 4 inches deep, and with a width about one-third the size of the plant. For example, if the entire plant measures about 12 inches in diameter, from leaf tip to leaf tip, it should be in a pot no bigger than 4 inches in diameter. After repotting -- especially if too large a pot was used -- African violets may stop blooming until their roots grow into the new potting medium and hit the the sides of the pot.
African violets bloom best when there is a single crown per pot. If you notice new crowns (they look like new little plants) developing from the stem you should remove those crowns. You can root these for new plants if you wish.
Disciplining a shrinking violet
If you still can't get your African violet to bloom, you can threaten it (seriously!). Do this by lifting the pot up a few inches then dropping it a couple of times onto a slightly giving surface, such as wood or folded newspapers to avoid breaking the pot. Or try thumping all around the sides of the pot with your fist. This slight disturbance of the root system can sometimes trigger sort of a survival of the species reaction, causing the plant to produce flowers.
-- Nancy Rose is a research horticulturist at the Minnesota Landscape Arboretum. To ask her a gardening question, call 612-673-9073 and leave a message. She will answer questions in this column only.