Starting a perennial garden from seed is an inexpensive way to add variety to the landscape. Unlike bedding plants, seeds give you a greater choice of flowers to choose from. Begonia is a tender perennial that thrives in shade. These flowering plants are available in a large variety of colors, plus there are varieties that sport ornamental variegated foliage. The tuberous-rooted varieties are the ones most often used as bedding plants that can be grown successfully from seed.
Place a ½-inch layer of gravel in the bottom of a seed-starting tray to aid drainage. Fill the pot to within 1 inch of the rim with a fine-textured, sterile seed-starting potting soil.
Fill the drip tray with 2 inches of water. Set the seed-starting tray in the water and leave it in place for two hours or until the soil feels moist.
Sow begonia seeds on the surface of the soil, about three seeds per inch in rows 1 inch apart. Press on the seeds with your fingertips so they are in contact with the soil but are not buried.
Cover the top of the tray with plastic wrap. Set the pot in a brightly-lit area that is not in direct sunlight. Keep the temperature between 70 degrees and 75 degrees Fahrenheit. Seeds germinate in eight to 10 days.
Peel back one corner of the plastic wrap two days after the seedlings appear to allow for airflow to the plants. Remove the plastic wrap entirely when the plants are five or six days old.
Water the begonia seedlings before the soil surface dries completely. Water slowly from the top or place in a drip tray of water to absorb the water. Take care not to wash out the seedlings when watering, as they have shallow roots.
Transplant the seedlings when they have three sets of leaves or when their leaves begin to overlap. Lift them out of the soil by their top leaves, then plant them into the same soil mix in a different tray. Space them 2 inches apart in all directions.
Move the seedlings into 4- to 6-inch-diameter pots when their leaves begin to overlap again. Plant one begonia seedling per pot, at the same depth it was at in the seedling tray. Alternately, transplant them directly into a flower garden if all danger of frost has passed.