Fibrous root begonias, also known as wax begonias, are propagated from seed. The seeds are exceptionally small and have a low germination rate, so many people prefer to purchase nursery-grown seedlings for their gardens. If you would like to experiment with starting your own begonia seedlings or are in need of a large amount of bedding flowers for less money, starting your own begonia seedlings may be worth it. Plant more seeds than the amount of plants you need to make up for the low germination rate.
Fill a seed starting tray with a sterile potting mix. Water the mix until it is evenly moist throughout but not soggy.
Sow begonia seeds in rows 3 inches apart directly on the soil surface. Seed in rows as thinly as possible because of the small size of the begonia seed.
Mist the surface of the soil with water in spray bottle, taking care not to wash the seeds under the soil surface. Cover the trays with plastic wrap and place them in a warm, well-lit room.
Remove plastic wrap once seedlings emerge, approximately 10 to 15 days after sowing. Place seedlings in a warm, brightly lit window or under grow lights that are positioned 4 inches above the tops of the seedlings.
Thin seedlings to one plant every 4 inches once they produce their second set of leaves. Cut off the weaker seedlings at soil level using small scissors and leave the strongest plants to continue growing.
Keep the soil moist at all times. Transplant begonias outside once all danger of frost has passed or into individual pots once they produce their third set of leaves.