Begonias can be started from seeds at any time of the year. If you plan to transplant your begonias into flower beds or outdoor containers, however, you should start your seeds in September or October. This allows the seedlings to become strong enough so the plants will flourish after they are transplanted in April or May. Begonias also make beautiful houseplants, with their showy blooms and rich green foliage.
Sterilize the clear plastic storage container and the clear lid by washing it with water mixed with a small amount of bleach. Use roughly 1/4 cup of bleach for every gallon of water. Rinse the container thoroughly and dry it.
Make a 50-50 blend of peat moss and perlite to use as the potting soil for your begonia seeds. Fill the 1.5-inch pots to the rim with the soil mixture, less 1/4 inch for watering. Press the soil into the pots to avoid future settling.
Mix the fertilizer so that it is 1/4 of the recommended strength for adult plants. Make the fertilizer water with boiling water; the heat will sterilize the potting soil and soak into the peat moss more effectively.
Add the boiling fertilizer water to a metal pan or tray, covering the bottom with about 1/2 inch of water. Set the pots with soil into the tray so that the soil mixture will absorb the water. Leave the pots soaking in the tray for about 30 minutes so the water will cool before planting the seeds.
Fold a clean sheet of paper in half. Empty your begonia seeds onto the center of the fold, carefully. You’ll see that the seeds are tiny. Pour about 50 seeds into each of the pots. You may wish to remove the pots from the water tray before adding the seeds, just in case you lose some in the water. Do not cover the seeds or tamp them down; begonias need light to germinate.
Place the pots back into the water tray for about 30 minutes to absorb more water, and then place each pot onto a cloth or paper to dry before you place it in the plastic container. Place the cover on the container. Check the pots daily and add water as needed to keep the mixture moist.
Place the plastic container filled with pots beneath a fluorescent light. Place the light 6 inches or less above the lid of the container and leave it on for at least 14 hours each day. Your begonia seeds will germinate anywhere from four to 30 days.