Sunday, December 29, 2013
Phew! I've just finished planting the last of the begonia crosses I made this year. This is the third batch of seeds I've planted, for a total of about 25 unique crosses using around a dozen different parents. The seedlings from the first and second batches are already good-sized so I'll need to do some repotting soon! This photo gives some idea of just how small the seeds are--generally about 0.5 mm in diameter:
Begonia seeds, ready for sowing
My experience with growing and breeding gesneriads gave me a good head-start with begonias. With both groups, the tiny seeds must be sown directly on the soil surface. I've always heard they require light to germinate, but I've never tested this as they just go on my light stand anyway, in clear or translucent plastic boxes that help keep them warm without drying out.
For sowing begonia (and gesneriad) seeds, I've generally had good results using Pro-mix. This year the garden center where I usually buy it was all out, so I tried Espoma Organic Potting Mix instead and have had similarly good results. The sowing medium should be fairly fine (I pick out the largest grains of perlite), well-drained, and not have fertilizer added. I find that mixes that contain fertilizer tend to burn the seedlings. I generally see the first seedlings within a week, and within two or three weeks the pots will all look like this--assuming the crosses were successful!