Start tuberous begonia tubers indoors about 6 weeks before the last frost date. Place them in a shallow container filled with a growing medium that is porous but moisture retentive and does not contain fertilizer or manure. Coarse sphagnum moss, peat moss or a good potting mix will all work. Completely cover the tubers with the growing medium. Keep the growing medium moist but not soggy. Place the container in a warm spot with filtered sunlight.
