How to Grow a Florist’s Gloxinia

Florist’s gloxinia ‘Kaiser Wilhelm’, by far the most popular variety. Photo: bakker-hillegom.nl

The florist’s gloxinia (Sinningia speciosa) is most often grown from a tuber, one usually sold in early spring along with the “summer bulbs” (gladiolus, dahlias, cannas, tuberous begonias, etc.). But it certainly isn’t a summer bulb like the others, notably because it’s almost always grown as a houseplant while the others will be planted outdoors.

How to grow this spectacular plant? Read on and you’ll see!

What Is It?

The florist’s gloxinia is in the Gesneriad family, the best-known member of which is the African violet (Streptocarpus ionanthus, formerly Saintpaulia inonantha). There are similarities, such as softly hairy leaves and a basic rosette shape, but differences as well. 

For one thing, the gloxinia is a larger plant (about ½ to 1 foot/15 to 30 cm) in height and diameter and has much larger flowers (up to 4 inches/10 in diameter) that are distinctly tubular rather than flattened. Also, while the African violet can grow and bloom all year long, the florist’s gloxinia is a seasonal plant. Just under the soil or partly exposed is a tuber: a hard, potatolike structure. After a few months of growth and bloom, the plant goes dormant, losing its leaves, and “retreats” into its tuber. It will then remain dormant for as few as 3 weeks, but sometimes 6 months or more, then starts to grow again, starting a new cycle.

How to Grow a Florist’s Gloxinia

1.     Starting From a Tuber

When you buy a tuber in the spring, it usually already has one or several sprouts at the top. You can pot it up right away or wait a few weeks or even months: just spritz the tuber with water if you find it becoming wrinkled and it will plump up again. It won’t need light until you plant it, so you can keep it in the dark, at cool to room temperatures, while you wait. To decide when to start a flowering cycle, consider it will usually start to bloom within 2 months of being planted. So you can get it to bloom in mid to late spring, summer or even fall depending on when you pot it up.

Plant the tuber into regular houseplant mix, setting the tuber in soil and filling in all around it, but leaving the top (where the sprout is) uncovered or just barely covering it. A 6-inch (15-cm) pot is usually large enough for a young tuber, although there are dwarf varieties better suited to 4-inch (10-cm) pots.

Water moderately, moistening the mix. As the plant “comes to life”, its watering needs will increase. Water it regularly, when the surface of the soil is dry to the touch. Don’t let it dry out during the growth phase or it will wilt and may lose some its leaves or abort its flower buds.

2.     Preparing Bloom

Move the plant to bright light, if possible with some direct sun. Yes, I know that many sources insist there should be no direct sun, but I disagree. A few hours of direct sun daily, as long as it is not overly hot, gives a denser, sturdier plant. It will do well, for example, near an east or west window, but back from a south one if it gets very hot there. Or draw a sheer curtain between it and the sun during the afternoon. It will also grow wonderfully about 6 to 12 inches (15 to 30 cm) under fluorescent or LED lights using a timer set at 14-hour days or longer. 

Although you sometimes see the florist’s gloxinia recommended as a shade plant, that would only apply to outdoor growing. Indoors, it really requires bright light to do well.

The florist’s gloxinia is fine with normal indoor temperatures (60–75 ?F/15–24 ?C) and average room humidity spring through summer, but may find the air too dry if you push it into bloom during the winter heating season. If so, consider using a humidifier or a humidity tray. Do not spray the leaves in a vain effort to improve the humidity: that has almost no effect other than staining the leaves and flowers.

Fertilize it regularly too, using your choice of fertilizer. A constant feed method, where you add a small amount of soluble fertilizer (about ? of the recommended monthly dose) at each watering, usually gives the best results.

3.     When Flowers Appear

Keep up basic care as above, including watering, making especially sure not to let it dry out. As mentioned, if yours is on a fall or winter bloom cycle, it may need extra humidity to keep the flowers from drying out.

The buds are impressively large and open into large flowers. It can remain in bloom for about two months.

4.   When Flowers Fade

Usually, the plant goes dormant soon after blooming. You can simply stop watering and, when the foliage starts to wilt, cut the foliage off.

5.     During Dormancy

Store the plant dry, still in its pot. (You can also remove the tuber from its pot and store it bare, but that involves extra effort on your part.) It will need no water until it starts to wake up on its own weeks or months later, nor will it need light. You can place in a dark basement or a closet if you like. It prefers cooler temperatures during dormancy, down to 45?F (7?C), but that is not absolutely necessary. It will do fine under regular room temperatures.

Check the tuber monthly while it is dormant, especially if it is bare, and if it seems to be shrinking and wrinkling, spray it lightly with water. Potted tubers are less exposed to drying out and won’t likely need spraying.

As mentioned above, when the tuber does sprout, you can either move it to the light immediately and start watering … or leave in dormancy for weeks or months.

6.     Repotting

You can usually grow florist’s gloxinias in the same pot for 2 or 3 years. After that, just as the tuber starts to come out of dormancy, unpot, removing all old soil and roots, and repot into fresh mix. As tubers grow in size over time, you may want to move it a larger pot.

Outdoors?

Florist’s gloxinias are rarely grown outdoors, not being tolerant of cool night temperatures (they should not be exposed to temperatures below 55?F [12?C] while in bloom). Plus, most cultivars have upward-facing trumpet flowers that are highly subject to rain damage. In tropical climates, hardiness zones 11 to 12, varieties with nodding flowers can be tried outside where they do best in dappled shade.

Multiplying a Florist’s Gloxinia

Seed

The florist’s gloxinia is surprisingly easy to grow from seed, especially since most other houseplants are not. 

You can purchase seed in seed catalogs or online. You’ll discover the seeds are very fine indeed, almost dustlike. Just sow the seeds lightly on the surface of a pot of premoistened soil, spray lightly with tepid water and cover with a clear plastic dome or bag. Place in good light (light is needed for germination), but without any direct sun, at fairly warm temperatures: 70 to 75?F (21 to 24?C). 

When the seeds sprout, which can take from 1 to 3 weeks, keep the tiny seedlings under plastic for a while. During that time, they’ll probably need no watering or special care. (The advantage of growing plants inside an essentially sealed container is that the air remains humid and the potting mix doesn’t dry out, saving you a lot of effort!)

When the plants are either about 1 inch (2.5 cm) in diameter or start to become overcrowded, remove the plastic cover gradually over about one week to acclimatize them to the drier outside air, then carefully transplant each seedling into its own individual pot. Grow them on as above.

They usually bloom quite quickly, in about 5 to 7 months from seed.

Stem Cuttings

Often the tuber will send up more than one sprout as it comes out of dormancy. You can let these grow, but also use the extras as cuttings. If so, when the sprouts are about 1 ½ inches (3 to 4 cm) tall, simply break any excess ones off at the base and root them in moist soil. They’ll develop a new tuber by the end of their growing season and so can be maintained for years.

Leaf Cuttings

This is a bit iffier. Sometimes it works, sometimes it doesn’t! You’ll have more success if you harvest a leaf near the beginning of the growth cycle than at the end.

Just cut off a leaf where it joins the stem and insert the petiole in a pot of moist soil … exactly as you would for an African violet leaf cutting. You can even cut a large leaf into sections and root each one! Cover the container with a clear plastic bag or dome, keep it warm, supplying light but no direct sun … and wait. 

Sometimes a plantlet comes up rapidly. If so, gradually remove the bag, repot it and move it to a brightly lit spot. It will soon bloom, although usually only modestly on a small plant the first time. By the second year, it will be full size.

Often, though, nothing seems to be happening and months can go by with no change, but don’t give up hope. There’ll be a small tuber forming in the potting mix, out of sight. Sometimes it sprouts and gives you a new plant, but other times it remains stubbornly dormant and no new growth appears. Why this happens remains a mystery.

Tuber Division

This is a bit risky, as cut tubers are subject to rot, but if you’re willing to take a chance, when the tuber sprouts in the spring and there are two sprouts, you can carefully cut the tuber in half between the sprouts with a sterile knife and pot up the divisions. Leave the tuber exposed for a week or so until the cut calluses over before potting it up. Even so, it may be worth spraying or soaking the cut in fungicide. Keep the cut tuber a bit dry at first until growth is well underway.

Varieties

There used be to a great deal of choice in varieties of florist’s gloxinia, but most of those named varieties seem to have been lost. These days, the only cultivars I regularly see sold as tubers are some of the truly ancient hybrids, dating back to the 1850s, like ‘Kaiser Friedrich’/‘Emperor Frederick’ (red with a white edge), ‘Kaiser Wilhelm’/‘Emperor Wilhelm’ (purple with a white edge), ‘Mont Blanc’ (white) and ‘Tigrina Blue’ (white with numerous purple spots and a purple edge), all single flowering. From seed, you can also find double and dwarf varieties. Usually these come in mixed colors: red, purple, lavender, pink, white and various bicolors. 

All the above are peloric varieties (first discovered in 1845 and called, at the time, Darwin’s peloric gloxinia), with symmetrical, upward-facing trumpet flowers. The wild Sinningia speciosa, though, had nodding, bilaterally symmetrical blooms. You can sometimes find seed of nodding varieties throughout specialist growers. 

Problems

• Weak, floppy stem: too little light.
• Leaf scorch: too much direct sunlight.
• Leaf spotting: misting or water spilled onto leaves during watering.
• Leaf rolling at the edges: dry air.
• Rot: overwatering, especially constantly soggy soil.
• Browning or blasting of flowers: dry air or drought conditions.
• Wilting stems, leaves and flowers: drought conditions.
• Flower thrips: tiny brown spots on leaves and flowers that build up over time. Also, pollen spills onto flowers. Blowing on the flower stimulates movement, making the tiny insects visible. Blue sticky traps and carefully spraying with insecticidal soap can help control them.
• Aphids: small, soft-bodied insects, usually yellow or pale green, are seen; white dead skins accumulate; new growth is distorted. Best controlled by removing and destroying all growth, thus forcing the plant to resprout from the tuber. 
• Cyclamen mite: dwarfed, thickened and wrinkled leaves. Infested plants fail to bloom or blossoms are misshapen. The mite itself is microscopic. Control is difficult. It may be best to destroy the plant.
• Gray mold (botrytis): gray moldy growth appears on leaves. Remove damaged leaves and reduce air humidity.

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Florist’s gloxinias: tubers are available in your local garden center every spring, so why not try one?