Begonia Growing Guide
Begonia (Begonia spp.) is an annual flowering plant when grown in cooler climates, but are perennial plants in their native moist tropical and subtropical climates.
There are hundreds of varieties whose flower colors range from red, pink and white. There are many varieties with large attractive variegated leaves.
Some varieties are only grown as annuals and discarded at the end of the season. Others are known as tuberous begonias and are hardy in USDA zones 8 to 10. In colder areas they need to be lifted out of the ground at the end of the season, with the tuber stored over the winter.
They bloom from late spring to fall and have a typical height of 10 to 12-inches.
Starting From Seed
Follow the seed packet instructions. Annual variety seeds can be started indoors 8 to 12-weeks before your last expected frost date.
The begonia seeds are very small and need light for germination. The seeds should be lightly pressed into the surface and may take up to 3-weeks to germinate.
For more detailed information visit the seed starting page.
Soil Preparation
Plant in full sun to part sun in a nice loose well-drained garden soil and they will do best in a slightly acid soil with a pH range of 6.0 to 7.0. In very warm climates they will do better in an area that gets some part shade.
Planting Annual Varieties
Annual varieties should be planted in the late spring 1 or 2-weeks after the last expected frost.
Plant begonia according to the plant tag 8 to 12-inches apart or in groups of 3 or 5 behind other shorter plants. In general you can plant the dwarf varieties 8-inches apart and taller varieties 12-inches apart.
Dig a hole as deep as the pot and twice as wide. To the soil you just removed add the same amount of good garden soil so you have a nice blend of new and native soil.
Take the plant out of the pot and gently loosen the root ball pulling away any roots that have grown in a circle around the pot.
Place the root ball in the hole with the growing crown even with or an inch higher than the surrounding soil. Gently spread out the roots and back fill the hole around the root ball leaving a shallow depression around your plant. Fill the depression with water to settle the soil around the roots adding more soil if necessary and water again. Water daily tapering off as the roots grow and get established.
Planting Tuberous Varieties
Plant begonia in the spring after all danger of frost has passed. Very large tubers can be divided in the same way as dividing potatoes.
Prepare your tubers a day or two before planting. Carefully look at the tuber and cut the tuber so that each section has at least one or more growing points or eyes on each. It is important to let the cut surface dry and heal over. After cutting, place the cut pieces in a single layer and let them air dry for 1 or 2-days to let them scab over. If you have problems with fungal diseases, dust the tubers with powdered sulfur to help prevent rotting.
When purchased by the bag full from a garden center it may not be readily apparent which way to plant them. One side will be rounded, which is the bottom where the roots will come from. The top portion may look flat or depressed, which is where the growth will come from.
The tuberous varieties should be planted with the tuber 1 or 2-inchs below the soil surface. Water them in and then daily, tapering off as the roots grow and get established.
A large mass planting makes an impressive floral display.
Watering and Care
Begonias are low maintenance and easy to care for. All you need to do is add a layer of mulch to help retain moisture and keep out competing weeds. Keep the mulch a few inches away from the stem.
They should get an inch of water each week and during dry spells give them some water to keep the soil moist. They usually do not need any fertilizer, but a light side dressing of organic fertilizer can be placed around the plant in the spring.
To encourage more flowers pinch off the old spent blooms.
In the late fall as the foliage yellows or just after the first frost kills off the foliage of the tuberous varieties the tops can be broken off. They should be lifted out of the ground before a hard freeze hits. Put the tubers aside in a dry place to dry out. Break off any stems and roots and shake off any remaining soil. To prevent any fungus problems you can sprinkle some dusting sulfur on the tubers.
Wrap each dry tuber in newspaper and store in a cardboard box or paper bag in a cool dry location.
Diseases and Pests
Bacterial leaf spot (Xanthomonas campestris), is usually caused by excessive humidity and high temperatures. Remove affected leaves with leaf spots as well as any dead leaves.
Botrytis blight (Botrytis cinerea), causes the stems to rot and the lower leaves turn yellow and fall off. The entire plant may appear wilted and collapse. It is difficult to treat and the plant should be tossed out. If it is a variety you want to keep try propagating with a leaf cutting.
Powdery mildew fungus (Erysiphe cichoracearum) causes white spots to form on the upper and lower leaf surfaces. Poor air circulation and humid conditions in shady locations increase the occurrence of powdery mildew. When it occurs remove infected leaves and flowers. If the plants are crowded, remove the entire plant to increase air circulation between the remaining plants.
Always toss all infected plants in the trash, not the compost pile.
Popular Begonia Varieties
The Boliviensis, Reiger, Tuberous and Wax varieties are the most common annuals found in garden centers. The Rex varieties are easy to care for houseplants that have beautiful variegated leaves in shades of bronze, purple, pink, red and silver.
Sources: Brecks, Eden Brothers, Park Seed.
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