Jennifer Schultz Nelson
Extension Educator, Horticulture
This time of year I find myself craving color around my house. After all the holiday decorations come down, everything is a little dull when surrounded by the winter dreariness outside.
Many stores will have great specials on indoor plants this time of year. A little greenery certainly is a pick-me-up, but what about more color? You may immediately think of flowering plants, but they can be pricey to buy in full bloom, the blooms last a limited amount of time, and not everyone has the right environment in their home to keep them alive and looking good.
Consider using plants with colorful foliage indoors. Generally speaking, these colorfully variegated plants will need more light than plants with leaves that are only green. Without sufficient light, the variegation will not develop, and leaves are solid green. Even though they need more light, typically they need far less light than most flowering plants do.
One group of plants with an incredible level of diversity in foliage color and pattern is the rex begonia. These plants are grown specifically for their foliage. They do flower, but the flowers are usually not very showy.
The "discovery" of rex begonias was a very serendipitous event. There are a couple versions of the story floating around, but the most dramatic one says that back in 1856 Belgian horticulturalist Jean Linden received a shipment of orchids gathered in India by plant collector Charles Simmons, and spied a small, rhizomatous, unusually colored plant in with the orchids that he named Begonia rex.
A rhizomatous begonia is one which the stems are thick and grow horizontally along the ground. Most will produce roots as well. The original Begonia rex was rhizomatous, and had dark leaves with a silver band. It was bred with other rhizomatous begonias available at the time, ultimately creating a whole new group of begonias, technically named a "cultorum", because all the members were cultivated. This new group of begonias became an exceedingly popular houseplant, especially for people in Victorian times.
The name "rex" comes from the Latin word for "king". Few would argue this name assignment, given the wide variety of showy foliage available in this group of begonias. Technically, rex begonias are still rhizomatous, but since they have been selected mainly for foliage color and form for so long, they have lost some characteristics of their rhizomatous ancestors, namely showy flowers.
Though they may lack showy flowers, rex begonias make up for it several times over with their gorgeous leaves. They may be bumpy or smooth, streaked with colors such as white, pink, yellow, or purple, and come in as many shapes as you can imagine.
There are some that grow in a whorl, resembling a living sea shell. One called Begonia 'Escargot' looks like a cluster of large snail shells. I recently ordered 'China Curl', which has deep spirals on a chocolate brown leaf with a silver streak spiraling to the center. I also ordered 'Curly Fireflush', which has great spriraling, plus the flowers it produces are fragrant.
There are many sizes of rex begonias available, from large specimens suitable for large patio or hanging pots, or miniatures perfectly suited for terrariums. Another begonia I'm eagerly awaiting is 'Tiny Bright', which stands six inches tall, but in that short stature manages to produce leaves each with bands of black, red, white and green.
Many articles classify rex begonias as "difficult" or "fussy" plants, but don't let this scare you from trying to grow them. Their colorful displays make the extra care worthwhile. And the extra attention will likely benefit your other plants as well.
The big "extra" that rex begonias need is humidity. Crispy brown edges on the leaves are usually a sign that the humidity is too low. Generally, rex begonias need in excess of 50% relative humidity. This can be hard to achieve in homes during the winter.
One way to increase humidity is by placing your begonias on trays filled with water and pebbles, without the water actually touching the pots. Running a humidifier in the room is another option, one that will probably benefit your other houseplants, as well as the human residents of your home!
While they thrive in high humidity, begonias will not tolerate wet feet. In fact, if kept wet too long, they will probably succumb to mildew and botrytis, both fungal diseases related to excessive moisture which turn your plant into a mushy rotten mess. I've killed a few begonias over the years because of overdoing the watering. It is very easy to do.
Two ways to counteract overwatering is to make sure there is good air circulation around your plants, and use a potting mix with excellent drainage. Also strive to avoid "calendar watering"–watering on a strict schedule. Learn to inspect your plants and assess whether they need water, no matter what the calendar says.
In general, the top of a rex begonia's soil should just begin to dry out before watering again. To determine whether it's time to water, let your fingers tell you. Don't be afraid to stick your fingers in the soil and check. They're better than any of the overpriced gadgets I've ever seen for sale!
Rex begonias need bright, but indirect light. Direct, hot sunlight will bleach out their brilliant colors. Morning or late afternoon filtered sunlight is acceptable.
As far as temperatures for rex begonias, if you are comfortable, your rex begonias will be too. They need temperatures higher than 60 degrees and thrive at temperatures around 70 degrees during the day. Some rex begonias will go dormant during the winter, and lose all or most of their leaves. As long as the stems remain plump and firm, water sparingly until spring, when growth should resume.
Rex begonias are relatively slow growers, but benefit from using a balanced fertilizer during the growing season to maximize color development in the foliage.
Rex begonias need little shaping or pruning, except as needed if bare sections develop, or you want to propagate your plant. Cuttings will root easily in water or damp peat moss. Leaves can be cut into wedge-shaped sections, and the narrow end inserted into damp peat moss as well. Create a "tent" with a plastic bag to increase humidity around the cuttings, and within a couple of months you should see small plantlets at the base of the leaf sections, and roots on the stem cuttings. Both stem and leaf cuttings are vegetative methods and will produce plants exactly the same as the parent plant.
Seeds are sometimes used for propagation, but realize that the seedlings will not necessarily resemble the parent plant. Seeds are more useful when crossing plants to produce new cultivars. Another method used to produce new cultivars is radiation induced mutation, a form of "mutation breeding". Sometimes chemical exposure is used to induce the mutation, but in the end the result is the same.
In mutation breeding, plant tissue is exposed to radiation or chemicals which change the DNA sequence in the plant. Depending where the change occurs, this may change the plants color, leaf shape, size, or may kill the plant.
This procedure is one way to "jump start" breeding efforts and generate a lot of individuals to select from in one generation. The desirable individual is selected and used to cross with other plants, or more likely vegetatively propagated to increase plant numbers while preserving all of the desirable traits.
Besides begonia, other horticultural crops, such as poinsettias, chrysanthemums, lilac, sweet potato, and grapefruit have all benefited from mutation breeding. Mutation breeding can be thought of as a man-made version of plants "sporting" in nature.
Sporting is when a natural mutation occurs in part of a plant, and that section, the "sport" appears different from the rest. Natural mutations can occur for many reasons; including exposure to UV rays in sunlight, as well as accidental mistakes in cellular machinery that duplicate a plant's cells during growth.
In crops that take a long time to reach maturity, like tree fruits, or ornamental trees and shrubs, this is a huge advantage. Rooting cuttings of "sports" takes a lot less time than trying to breed desirable traits by crossing plants and cultivating seedlings over multiple generations.
If you do choose a rex begonia for your home this winter, consider that they are not only beautiful, but there is a lot of complicated biochemistry underlying that beauty. In my opinion, that biochemistry deserves the title of beautiful too.