While commonly referred to as “gloxinia” or “florist’s gloxinia,” this plant (Sinningia speciosa) is not a true gloxinia at all. True gloxinias do not produce tubers but sinningias do. Florist’s gloxinia is a herbaceous perennial and a member of the Gesneriaceae family, to which the popular African violet also belongs. It is native to Brazil.
Gloxinias are among the best plants that are grown for spring and summer enjoyment, although with proper handling, flowering plants can be produced throughout the year. Their velvety, bell-shaped flowers can average over 3 inches in diameter. Each flower is displayed on a long petiole. Their color-range is white to pink to red to blue to purple. They can also be two-toned with white centers or white rims. There are single and double flowering types, with petal edges smooth or wavy. Their foliage is oblong, graceful and velvety like their flowers. Gloxinia will not be outdone for showmanship.
Propagation: Gloxinias can be grown from seed, tubers, or leaf or stem cuttings. Tubers are available only for spring plantings — plants from tubers are in flower in about four months. Producing flowering plants from seeds takes about six months, depending on the seasons involved (e.g., they grow a lot faster in summer than in winter). Plants grown from seeds have shorter internodes (the area of a stem between points of leaf attachment). As a result, they are more compact and more attractive.
Growing Media: Gloxinias grow well in a mix that contains 50 percent sifted peat (using a sieve with quarter-inch openings) with the remainder being a combination of perlite, coarse sand and a little vermiculite. The pH should be 5.5 to 6.5.
When potting a tuber, make sure that the “hollow” part is on top and very close to the mix’s upper surface. Gently pack the dry growing medium around the tuber and then water many times (maybe even 10 times). Never pack any growing medium that is wet.
Light & Temperature: Bright, indirect light is necessary to keep gloxinias in flower. They are “warm loving” plants that grow best at a nighttime temperature of 65 °F or warmer. The preferred daytime temperature is 75 °F. Gloxinia leaves are somewhat brittle, which is made worse by temperatures lower than those recommended.
Watering & Fertilizer: Gloxinias should never be allowed to dry out, even slightly. When watering, avoid getting water on the leaves. Humidity should be high. This can be achieved in the home by placing the plant on a gravel/water tray. Gloxinias should be fertilized moderately at every watering. Avoid fertilizers with high phosphates and urea nitrogen. A balanced fertilizer such as a 15-15-15 is recommended and should be applied according to label directions.
Flowering: Gloxinias are extremely sensitive to their environment. They simply do not tolerate stress well. Anything that restricts their root growth or top growth will reduce both plant size and the number of flowers initiated. A single gloxinia plant can produce well over two dozen flowers. If the first two flowers are pinched off very early in their development, the majority of the remaining flowers will develop together, making a spectacular display.
When all flowering is completed, the plant will decline and go into a resting state. As the plant declines, start watering less often, then stop watering altogether and let the leaves die. Allow the tuberous stem to rest 2 to 4 months in dry soil. Keep an eye on the plant and when new growth appears, resume watering.
Diseases are an infrequent problem in the home environment. Gloxinia may develop root rot from overwatering. Leaves may be damaged by cold water, so keep water off of the foliage. Insect and related pests of gloxinias include mites and thrips.