Sunlight is important for all plants for photosynthesis, the vital function that allows plants to convert carbon dioxide from the air into usable plant carbohydrates. Even if all other requirements for a plant are met perfectly, without proper light, a plant will starve to death. African violets are especially sensitive to unfavorable lighting conditions.
The most common lighting condition that affects African violets is not enough sunlight. If the violet stops flowering and the leaves begin to yellow, it is telling you that it is hungry for more sunshine. Also, if the rounded leaves begin to look more elongated and the plant becomes “rangy” (grows long, spindly stems), it is telling you that you didn’t listen to it when it just stopped flowering and now has taken more drastic action to get your attention.
On the other hand, too much sunlight also makes violets unhappy. Too much or too bright sunlight actually sunburns the delicate leaves of the violet, producing brown “sunspots” on the leaves and flowers. Too much sunlight can also be the cause of the violet leaves turning down, in an attempt to try and protect itself from the sunburn. If you have not watered with cold water and you still begin to see your leaves curling downward, consider protecting it from some of the hottest, brightest sun of the day. Too much sun will also cause the leaves of variegated African violets to lose their lighter coloring, turning the entire leaf a uniform green.
African violets tolerate early morning or late afternoon sun, but do their best when they are never exposed to direct sunlight. They prefer to be in a window where they receive bright light for most of the day. If you have a fancy light meter, you can use that to measure the intensity of light that touches your violet, looking for readings of about 900 to 1100 foot candles or 10,000 to 12,000 lux. But, if you’re like me and don’t want to worry about all that fancy, schmancy equipment, you can estimate the light intensity by simply holding your hand 10 to 12 inches above the top of your violet during the brightest part of the day. If you can barely see the shadow of your hand, your violet is likely getting enough, but not too much, sun. If your only windows are exposed to direct sunlight, you can protect your violets with a sheer drapery or other type of barrier that allows light through but does not allow the direct, intense rays to touch the plant.
The amount and intensity of light varies greatly from season to season. In the summer time in North Dakota, violets receive 14 to 16 hours of bright, natural light per day, even in an east or north facing window. In the winter, however, they are lucky to get 6 hours of sufficient sunshine, even from a southern or western exposure. That is why mine move from the west facing patio door in the spring; spend late spring, summer and most of fall in the eastern exposed bow window and then back to the west when the days become shorter and shorter. I can’t leave them by the patio door once the sun begins to climb high in the sky, as the heat and brightness of the sun through those west windows becomes much too intense for them by late May to early June.
African violet growth is stimulated in direct response to where light touches their leaves and stems, so it is important to rotate the plant every time you water. Each watering should be accompanied by turning the planter a quarter of the way around, so at the time of your fourth watering, you will be back to your starting point. This will prevent you from growing a lop-sided plant.
An alternative to sufficient natural light is to use a broad-spectrum grow light. Violets must have the red spectrum to bloom, while the blue spectrum is critical for healthy foliage and sufficient absorption of nutrients. The grow light should be positioned about 18 to 20 inches from the top of the plant.
There are two considerations when using grow lights to stimulate blooms and healthy leaf production in violets. First, like many plants, they need a daily rest period of at least eight hours of darkness. You can accomplish this by turning off the lights when you go to bed at night and back on when you get up in the morning. If you don’t spend an eight hour night sleeping, you can consider using a timer to regulate the light and dark periods for your violets.
The other consideration is specific to African violets. While most plants don’t care overly much if the light they receive is natural or artificial, violets are more persnickety. They develop a condition called “Leaf Bleaching” if they are exposed only to artificial grow lights. Leaf bleaching shows up as much lighter areas on the leaves that are exposed to the most direct artificial light. These spots can actually turn pink, which may appear attractive at first, but they interfere with the plant’s photosynthesis capability, eventually affecting their growth and blooming. The only way to treat this is to discontinue the exposure to artificial light and grow them in natural, bright, indirect light.
Tomorrow we'll talk about temperature and humidity.