Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
What are Tuberous Begonias?
Tuberous begonias (Begonia × tuberhybrida) are begonia cultivars that are the result of hybridizing begonia species. They do not occur naturally in nature. They are all created by begonia growers who cross pollinated different begonia species in search of new and unusual begonias.
As a result of these crosses, tuberous begonias display a variety of flower colors and forms. Some have leaves that are burgundy or bronze instead of the usual green. These plants are shade lovers so their bright flowers and colorful foliage brighten up shady corners of your yard. They can be grown in the ground or in containers. There are cultivars that have pendant or trailing forms that look particularly attractive in hanging baskets.
The parents of tuberous begonias are all native to South Africa and South America, so they are not hardy in temperate climates. You can either grow them as annuals or dig up the tubers in the fall and store them indoors over the winter.
How to Plant Tuberous Begonias
You can purchase tuberous begonias as plants which can be planted directly into your garden after your last frost or as tubers that you can start indoors. The tubers are actually an enlarged part of the stem which stores food for the plants.
For plants that will bloom beginning in June, start your tubers indoors in February. For flowers in July, you can start your tubers indoors in either March or April.
The tubers have a top from where the plants grow and a bottom from which the roots grow. It’s easy to tell them apart. The top of the tuber has an indentation or hollow. When you plant your tuber, make sure the hollow is facing upwards.
Fill a container with peat moss or vermiculite. Don’t use soil. Plant the tuber in the peat moss or vermiculite so that it is barely covered and then moisten the medium. Keep it moist but not wet. The tubers rot very easily. Place the container where it will receive indirect light.
In about a month, roots should start to grow from the sides and bottom of your tuber and stems should start to grow from the top. When the stems are 1 inch tall, you can transplant the tubers into containers filled with regular potting soil. Each tuber should have its own pot that is 5 – 6 inches in diameter.
Move the pots to a sunny window or add supplemental lighting.
Small tubers should have 2 – 3 stems. Large tubers should have 3 – 6 stems. When they are 3 inches tall, thin out any extra stems. The flowers will be smaller if there are too many stems.
How to Grow Tuberous Begonias
You can move your plants outdoors after your last frost. In my zone 6 NJ garden, I like to wait until the end of May to move my tropical plants outdoors. Before that, the May nights can be very cold and occasionally we get surprise frosts in early May.
Choose a shady spot in your yard for these beauties. Too much sun can scorch the leaves. They can tolerate early morning or late afternoon sun. In between, they like dappled shade or indirect light. Too much shade will cause the plants to spindly.
You can use regular potting soil or if you are planting them directly into your garden, make sure the soil is well-drained. Keep them watered, either weekly 1 – 2 inches when grown in the ground or daily when grown in containers.
Tuberous begonias are what is known as heavy feeders which means that they use up a lot of nutrients in the soil very quickly. Fertilize them every 2 weeks with a diluted balanced fertilizer.
How to Store Tuberous Begonia Tubers During the Winter
After your first frost, it’s time to dig up your tubers. They will not survive outdoors over the winter. If your plants are in the ground, use a garden fork to lift them from the soil. If they are in a container, use a small trowel to lift them from the potting soil. Leave any attached soil. Trim off the dead stems leaving about an inch.
The tubers will need to cure before you store them. This helps them to dry out slightly so that they don’t rot while they are stored. Let them cure to 2 – 3 weeks. Then shake off the soil, then bury the tubers in peat moss, vermiculite or saw dust. They should be stored in an area that is 40⁰F - 50⁰F until you are ready to plant them in the spring.
How to Grow Tuberous Begonias From Cuttings
Unfortunately, you cannot grow more tuberous begonias by cutting up the tubers like you can with potatoes but you can grow new plants from cuttings. When you thin out the stems in the spring, you can root those stems.
Fill a container with vermiculite and moisten it. Plant your cuttings in the vermiculite and then cover the container with a plastic bag to create a mini greenhouse. Place the pot where it will get indirect light. You can mist the vermiculite if it starts to dry out.
The plants should have roots within 2 – 4 weeks. You can tell that they have roots if you see new leaves. Plants without roots cannot grow new leaves. Remove the plastic bag and transplant your new plants into pots filled with potting soil.
You can move your seedling outdoors after all danger of frost. Leave them in their containers or plant them in the ground. By the fall, they should have developed a small tuber which you can dig up and store like the larger, mature tubers.
© 2020 Caren White
Caren White (author) on December 29, 2020:
They make lovely hanging baskets. Thanks for reading and commenting.
Peggy Woods from Houston, Texas on December 29, 2020:
I have enjoyed tuberous begonias as hanging baskets in the past. Thanks for writing about this beautiful blossoming plant, and how best to care for it.