Dr. Leonard Perry, Extension Professor
University of Vermont
Begonias are an easy houseplant for beginners, with a range of species and selections for the more advanced gardeners. Some are grown for flowers, others for their foliage. They come in a range of sizes, shapes, and habit, from upright to spreading. Many tolerate low light, and they have few if any pests.
Let’s deal first with the main need for begonias indoors, especially in buildings with forced air heat, that being to increase humidity levels around plants. You can keep a misting bottle (as found in hardware or home stores) nearby and mist plants daily. If this will harm walls or furniture, try a humidifier (this will help the air for you as well). Placing plants on a tray of pebbles, and keeping this moist by watering the pebbles every day or two helps. If plants are under lights, or some form of plant stand, you can place plastic over and around this to maintain higher humidity within the “tent.” Many begonias will tolerate some dry air, but won’t thrive.
Keep plants watered, but not too wet. If in doubt, don’t water. Let soil dry between watering, then water thoroughly so water drains out the bottom of pots. But don’t let plants sit in a saucer of water. You can place water in a saucer under pots, letting the soil wick-up and absorb the water, just make sure to drain any left after an hour or two.
So what soil mix is best for begonias? Use a soil-less mix, one formulated just for indoor plants and usually containing peat moss and perlite or vermiculite. Don’t use amendments as you would in the garden, such as compost, nor garden soil. These may be good in the garden but behave quite differently in pots, keeping plants too wet and often introducing diseases.
Begonias don’t like too large of a pot, preferring to be pot bound. If you have a plant that takes days to dry out, perhaps the pot is too big and you should repot into a smaller pot. If pots are too large, the mix remains wet for too long and often leads to root diseases.
Provide fertilizer (according to label directions on product of your choice) when plants are growing. This actually might be in winter when leaves are off trees and more light may come in windows or be reflected off snow outside. Perhaps better when fertilizing is to use a product at reduced strength, but more often.
Begonias like it warm, not being happy below about 55 degrees (F). More ideal are temperatures between 62 and 72 degrees, with some difference between day and night.
Light preference varies with the type of begonia, so look for this on labels, in catalogs, online, books, or ask your garden retailer for advice. You usually won’t go wrong using bright natural light, but little direct sun (such as an east window) or filtered sun (as with sheer window drapes). Too much direct sun can “burn” leaves, causing discoloration or browning.
Good for most begonias is a supplemental light stand, which could be as simple as inexpensive shop lights with fluorescent tubes. Suspend these over plants, a few inches between the tops of plants and light tubes. Or you can use directed spot fixtures with full-spectrum light bulbs, if possible. Keep any lights on for about 14 hours a day, or in the evening to supplement daylight from windows during short winter days. Inexpensive timers from hardware or home stores work well for controlling lights.
If you end up with leaves staying too wet, as in a tented structure, a whitish disease called “powdery mildew” may cover leaf surfaces. Keep the plants drier and this should disappear. While begonias get few if any pests, keep an eye out for small white cottony masses, particularly where leaves join stems. These “mealybugs” are easily controlled by dabbing them with rubbing alcohol.
If begonias get too tall and leggy, you can root cuttings for more or replacement plants. Or just cut (“pinch”) plants back to the desired height, from which point they’ll grow sideshoots. If rooting cuttings, place in a mix of sand and peat moss, or perlite, keep moist, and keep humid as in a clear plastic bag over the pot (but check daily to make sure plants are too wet). Too tall and leggy may indicate too low light or too much fertility, or old plants needing rejuvenation.
The begonia family is huge, with over 1,600 species and thousands of selections. Some are grouped by root type. Those growing from a swollen yet flattened, brown tuber structure– the tuberous begonias– are best grown outdoors in summer in shade. Those from an enlarged underground stem or rhizome, or those with fine fibrous roots, generally grow well indoors. While the former are usually grown for their leaves and tolerate lower light conditions, the fibrous are usually flowering species for bright light.
You may see begonias grouped by habit, such as spreading, shrub, thick-stemmed, or cane types. Some recommend the shrub and cane types as better choices for indoors. The shrub begonias have multiple canes from the base to make a rounded plant. Cane begonias have tough jointed stems (think of bamboo canes). Another simple grouping consists of the flowering types, and those grown for the foliage.
Of the foliage begonias, the most common are the Rex begonias with their large leaves, perhaps 6 inches wide, in various shapes, and even more striking colors including reds, silver, green, pink, purple, and gray. These are usually rhizomatous, and often need more humidity and moisture than other begonias. All the variations you’ll find descend from one ancestor, a species native to the northeastern Indian state of Assam.
Of the flowering types, the most common may be the fibrous-rooted wax-leaf (often called semperflorens from the species name), and cane-type angel wing begonias. The names are descriptive of their leaves, and their small flowers come in various colors of reds, pink, and white. These are often the types you see and use in summer gardens, and which can be potted before frost in fall and brought indoors.
Elatior begonias are another flowering type, being semi-tuberous and specially developed for long flowering indoors. Angel wing have winged-shaped leaves, often with white or silver markings. These two types, the angel wing and wax-leaf, have been crossed to make the Dragon Wing begonia. They have the leaf shape of angel wing, but are green with no markings.
Another rather new and popular type, with solid green angel-shaped wings, is the Bolivian begonia, found growing naturally on the cliffs of Argentina. These are great in hanging baskets or pots, reaching up to 2-feet across and covered in flowers all summer. Popular examples are the bright orange Bonfire and scarlet red ‘Santa Cruz Sunset’.
If you want to see some of the range of indoor begonias, make plans to visit the greenhouses at the Montreal Botanical Gardens (espacepourlavie.ca/en/botanical-garden) where they have one of the top begonia collections in North America. (A great place to visit in winter in particular.) Or you can find more resources, with photos, from the American Begonia Society (www.begonias.org).
(author’s note: Any videos or ads appearing here, added by WordPress, are not in any way related to nor have been approved by the author.)