Use new seedling trays or flats to plant begonias from seed. The plants are prone to developing fungal diseases, including damping off and botrytis, so new or disinfected seed trays are a must. You’ll also need new sterile potting soil that’s formulated specifically for seed starting.

Once your seed trays are filled with sterile potting mix, it’s time to plant your begonia seeds. Begonias need light to germinate, so simply broadcast the seeds across the surface of the potting mix and press them against the surface of the soil with your fingertips or a flat piece of cardboard. Do not cover the seeds. Try to distribute them evenly across the soil, but it’s okay to have them spaced fairly closely. Begonias always need to be transplanted when they’re young, so if the seedlings end up too close, it’s no big deal; you’ll be separating them later anyway.

When I start begonias from seed, I water the newly planted seeds in with a mister, rather than a hose nozzle, to make sure they stay in place and don’t float away.

Cover the seeding tray with a sheet of clear plastic or a humidity dome, and place the tray under grow lights that run for about 14-18 hours per day and stand about 2-3″ above the tops of the trays. Put heat mats under the trays to improve and speed germination. Some varieties of begonias can take weeks, if not months, to germinate, so don’t give up on them even if it seems to be taking forever. Make sure the seed flats don’t dry out; water them with a mister or spray bottle whenever necessary. Remove the plastic or humidity dome as soon as the seeds start to germinate. Raise the lights as the plants grow.