How to Start Begonia Bulbs

Starting begonias from bulbs, or tubers, is the easiest way to grow them successfully.

Many gardeners consider Begonia x tuberhybrida difficult to grow and unforgiving of all but the most optimum growing conditions. It's true that they are a bit fussy, but certainly not impossible. Tuberous begonias can be started from seeds, but bulbs are typically much easier to manage. You can start begonia bulbs, or tubers, indoors in the spring and enjoy the plant's gem-like brilliance for many years to come.

Things You'll Need

• Scissors
• Half-gallon paper milk carton
• Peat moss
• Sand
• 6-inch pot
• Potting soil
• Bone meal
• Liquid fertilizer

Instructions

1. Choose large, firm begonia bulbs. Bigger tubers produce bigger plants with more blooms. Reject bulbs that are soft as these are probably rotten. Tubers that are shriveled are already dying.

2. Start begonia bulbs indoors in the spring, about eight weeks before the last predicted frost for your location. Use scissors to cut off one side of a half-gallon paper milk carton. Wash it thoroughly with hot soapy water and rinse well. Punch about a dozen holes in the bottom to allow for excellent drainage. Fill the bulb-starting flat to within ½ inch of the top with a mixture of equal parts peat moss and sand.

3. Plant the begonia bulb in the center of the flat, hollow side up so that it's covered with ½ inch of soil. Set the flat in a shallow container of warm water until the surface of the soil is barely moist to your touch. Remove it from the water and set it in the sink to allow it to drain freely for about two hours.

4. Set the flat in a warm spot with a constant moderately warm temperature range of between 65 and 70 degrees F. Keep the soil evenly moist, but don't allow it to become soggy or wet. Begonia bulbs are highly susceptible to rotting. Move the flat to a warm, sunny windowsill when the sprout emerges in about one to three weeks.

5. Step the begonia spout up to a 6-inch pot when it develops at least two true leaves. Mix three parts good commercial potting soil with one part peat moss. Add a little bone meal according to the packaging instructions. Water thoroughly to evenly moisten the soil. Keep it on the sunny windowsill and rotate the pot a quarter turn every two or three days to encourage the stem to grow straight.

6. Feed the young begonia every two weeks. Use a good liquid fertilizer. Follow the packaging instructions carefully.

7. Acclimate the begonia to the outdoors gradually once all danger of frost has passed. Take it outside and place it in a brightly lit shady spot that has good air circulation, but is well protected from the wind. Bring it in at night, but keep it at around 55 to 60 degrees F. After hardening off for a week, your begonia will be strong enough to leave out overnight. Continue to keep the potting soil evenly moist but never wet or soggy.

8. Move the plant into a brightly lit but partially shaded location thereafter. Plant outdoors in partial shade, if you wish. Increase feeding frequency to once weekly when flower buds appear. Continue throughout the blooming cycle.

Tips & Warnings

• The easiest tuberous begonias to grow are the multi-flora varieties, typified by many stems per bulb. Hanging types tend to be the most difficult. The grandi-floras fall somewhere in between, but require careful staking of tall, brittle stems.

References

• Washington State University: Tuberous Begonia
• Iowa State University: Growing Tuberous Begonias in the Home Garden
• North Carolina State University: Summer and Fall Flowering Bulbs for the Landscape