Jewel-toned, velvety bell-shaped flowers up to 3 inches across crowning rosettes of fuzzy, deep green foliage put gloxinias (Sinningia speciosa) high on the list of blooming houseplant favorites. Often with a speckled throat or contrasting petal margins, each brilliant blossom lasts up to a week during the plants' colorful two-month display. Whether seed-started hybrids or grown from tubers, all actively growing gloxinias require similar care.
One Year or Many
Florists’ gloxinias are seed-started hybrids bred for a single, showy annual display. Enjoy them while they last; then discard and replace them. For repeat performers, buy and plant gloxinia tubers in winter or early spring. Although tuberous varieties potentially grow as perennials in U.S. Department of Agriculture plant hardiness zones 11 through 12, their leaves' aversion to moisture makes them unsuitable as outdoor plants. After each blooming cycle, nurture the tubers through dormancy for years of enjoyment.
Watering and Feeding
Watering a gloxinia from underneath -- called subirrigation -- prevents overwatering and damage caused when water splashes on the leaves. Set the pot in a saucer of lukewarm water and let the plant absorb moisture for an hour. Repeat when the potting medium feels dry on the surface. For the largest, most vivid flowers, feed growing gloxinias every two weeks with a water-soluble, high-phosphorous fertilizer. A water-soluble 15-30-15 formula is suitable. Apply it to recently watered plants at the rate of 1/8 teaspoon to 1 quart of water, or the manufacturer's recommended rate, taking care not to splash the leaves.
The Well-Groomed Gloxinia
For tidy, long-blooming gloxinias, snip the faded flowers' stems off at the first set of leaves. To avoid accidentally spreading disease, disinfect your cutters in a solution of 1 part household bleach to 9 parts water as you move from plant to plant. When roots begin creeping from a container's drainage holes, it’s time move the plant to a pot one size larger for repotting in fresh African violet growing medium.
Crown rot and gray mold target overwatered gloxinias. Watering from beneath is the best defense against these diseases and also prevents leaf discoloration from splashing water. Most insects ignore the plants, but cyclamen mites may be a serious threat. Tiny enough to shelter in leaf folds or beneath leaf hairs, they distort, stunt and kill new growth. Isolate and dispose of affected plants, because the available treatments -- pesticides or hot-water immersion -- ruin the blooms and leaves.
Care During Dormancy
Once a tuberous gloxinia finishes flowering, remove the leaves. If you see no new stems, stop watering the dormant plant. When the medium is almost dry, move the pot to a dimly lit area. Maintain the temperature between 50 and 60 degrees Fahrenheit and moisten the surface of the medium as needed to keep the tuber plump. After growth resumes, repot it in fresh medium, move it to its old spot and continue regular care.