From summer through fall, tuberous begonias produce beautiful, showy flowers that measure up to 8 inches across. You can buy tuberous begonia plants, but many gardeners prefer to grow them from tubers. In most parts of the country, gardeners have to start their begonias indoors, transplant them to pots or flower beds when the weather warms up, and then bring them back inside in the fall.
Start begonia tubers indoors about a month before the last average frost date for your area, since they bloom about three months after planting. Contact your local county extension service to learn what that date usually is.
Fill shallow pots with damp potting soil.
Turn the tubers hollow-side up and set them in the pots about an inch apart.
Cover the tubers with about an inch of soil.
Water the tubers well one time. Thereafter, keep the soil damp but not soaking.
After the tubers have grown to 1 or 2 inches long, repot each one in a 6-inch pot or plant them permanently in big pots. Cover each tuber up with soil, to a maximum depth of 2 inches.
Choose the right location outdoors for your young begonia plants after the danger of frost has passed. They should get sunshine either in the morning or the late afternoon. Begonias don't do well in full, hot sunlight.
To plant the begonias in flowerbeds, place them into the soil eight inches to one foot apart, with the tops of the plants just above the surface of the soil. If your begonias are in large pots, move them to the spot you chose outside.
Fertilize your begonias regularly. Water them well but don’t let them get soggy.