Gloxinia

Identification and origin

Sinningia speciosa belongs to the gesneriad family, Gesneriaceae, along with African violets and streptocarpus. It is native to southeastern Brazil. The genus honors Wilhelm Sinning, head gardener at the University of Bonn; speciosa means “showy.” Despite its common name, it is not a true Gloxinia: species in that genus do not form tubers.

It is a perennial that regrows each year from a tuber. The hairy, purplish stems stay under 12 in, and the plant forms a mound 6–12 in tall and wide. The oval, velvety, scalloped leaves grow in a rosette and can reach 8 in long and 6 in wide: medium green with pale veins on top, pale green flushed with red underneath.

The velvety bell- or trumpet-shaped flowers often exceed 3 in across and rise above the foliage on long stalks. Colors range from white to pink, red, blue, and purple, including bicolors with white throats or white edges, speckled forms, and single or double flowers. A single plant can produce more than two dozen blooms. Florist’s gloxinias are hybrids with larger flowers in a wider range of colors; examples include the Brocade Series and ‘Carangola,’ with white flowers and a dark purple center.

Light

It needs bright but filtered light, more than an African violet. Set it near a bright window, just out of reach of direct rays, for example behind a sheer curtain. In spring and summer, direct sun burns the foliage and shortens the life of the flowers. Stretching stems, on the other hand, mean the light is too weak.

Watering

During growth and bloom, keep the mix evenly moist: never let it dry out, even slightly, because a gloxinia that wilts can be seriously damaged. Feel the surface before watering and water as soon as it starts to dry, without leaving the plant standing in water.

Never wet the leaves or the center of the rosette: water on the foliage damages the leaves and encourages crown rot and gray mold. Water at the base or into the saucer, using room-temperature water, since cold water damages the leaves. The air should be humid: set the pot on a tray of wet gravel, especially during the first weeks at home.

During active growth, give a moderate dose of balanced fertilizer at every watering, avoiding formulas high in phosphorus and urea.

Potting mix

It likes a light, acidic, well-drained mix rich in organic matter, for example a sifted potting mix lightened with perlite, a little coarse sand, and vermiculite. Aim for a pH of 5.5 to 6.5. Never pack down a wet mix: fill with barely damp mix, then water thoroughly.

Temperature

It likes steady warmth: 64–75 °F during growth, with nights no cooler than 64 °F and slightly warmer days, around 75 °F. Cooler temperatures make the leaves brittle.

During rest, keep the tuber cool and dark, at about 55–61 °F. Outdoors in the ground it is grown only in USDA zones 11a to 12b; elsewhere it can spend summer outside in its pot, out of direct sun.

Repotting

After flowering, the plant declines and goes dormant. Gradually water less, let the leaves yellow and dry, then cut them off. Keep the pot cool and dark, with the mix almost dry, for two to four months, checking that the tuber does not shrivel.

As soon as new shoots appear, lift the tuber, remove the old mix, and replant it in fresh mix, one tuber per 4–5 in pot. Set the hollow side up, with the top level with the surface. Then place it somewhere warm, bright, and humid, and gradually resume watering. Flowers return about four months later.

Pruning

Remove faded flowers to extend the bloom, along with yellowed leaves. After a first flush in spring, you can cut the stems back above the first two leaves to get a second bloom before dormancy. Pinching off the first two buds very early lets the following ones open together for a more spectacular display.

Propagation

• Leaf cuttings, in spring: choose a leaf at least 2 in wide, because smaller leaves lack the reserves to form good roots. Insert the leaf stalk in a light, moist mix and cover with a plastic bag to hold in humidity. Rot points to too little light, too much water, or poor air circulation.
• Stem cuttings: take young shoots 1–4 in long.
• Seed: allow about six months to flowering. Seed-grown plants have shorter internodes and are more compact.
• Tubers: a tuber started into growth blooms in about four months.

Common problems

• Buds that drop before opening: poor light, low humidity, or mix that has dried out.
• Damaged leaves: cold water or water left on the foliage.
• Scorched foliage: direct sun.
• Stretched stems: too little light.
• Crown or root rot, gray mold: overwatering, watering from above, or poor air circulation.
• Pests: aphids, scale insects, spider mites, thrips, root mealybugs, vine weevils, fungus gnats.
• Diseases: leaf spot, rust, powdery mildew.
• A plant that declines after flowering: often just the normal start of dormancy; check that the tuber stays firm.

The same symptom can have several causes: check light, watering, temperature, and humidity before acting.

Toxicity

Gloxinia is classified as non-toxic to dogs, cats, and horses. No toxicity has been reported for people either. If a pet or a child has eaten a large amount and shows unusual symptoms, contact a veterinarian or a doctor as a precaution.