African violets are attractive houseplants with flowers in a variety of colors ranging from purple and blue to yellows, pinks and white. The leaves of a healthy plant are a dark green with tiny fizzy hairs. Proper care of the African violet will prevent yellowing leaves.
African violet plants need indirect sunlight from an east or north window. If the plant is in a south or west window, the bright, hot sun can cause the leaves to burn and turn yellow. Plants that don't receive enough light will have yellowing leaves. Turn the plants a quarter turn every week so that each side of the plant receives some light from the window. Plants need at least eight hours of darkness as well to bloom. If using artificial light, the plant will do well with 600 foot candles, which is equivalent to two 40-watt fluorescent bulbs about 12 to 15 inches above the plant for 15 hours a day.
Broad mites are one pest of the African violet that will cause the upper and lower surfaces of the leaves to turn yellow. Besides yellowing, the leaves may curl around the edges. Broad mites will feed on the older leaves on the bottom of the plant. The pest is oval-shaped, about 1/100 inch in length, and is similar to the cyclamen mite that feeds on the leaves in the center of the plant and not the bottom leaves.
Stem or Root Rot
Plants that are overwatered can develop stem and root rot, which will cause the plant leaves to turn yellow and the plant to wilt. African violets need moist soil, but should dry slightly between each watering so the soil is never soggy. The leaves turn yellow as a sign of nitrogen deficiency. This happens because the soil is too wet for the roots to take up the nitrogen from the soil.
The lack of nitrogen in the soil can cause the leaves of the African violet to turn pale green and then yellow. The plant could need fertilizer if all other problems have been ruled out first. A specially formulated fertilizer meant for African violets found at most nurseries will provide the nutrients plants need to stay healthy. Fertilize plants once a month, but stop fertilizing during the winter, unless the plant is grown under artificial light.