Pretty petunias bloom and add color to the garden all summer long. They flower profusely in beds, borders, containers and hanging baskets. While petunias are available as transplants from nurseries in spring, it is much less expensive to start your own bedding plants from seed. Growing petunias from seed also gives you a greater variety to choose from, as nurseries sell only a few varieties as seedlings. Petunias are ready to be set out in their permanent garden home after all frost danger is past in spring.
Fill a seed-starting flat to within ¼ inch of the rim with a sterile potting mixture. Set the flat in a tray filled with lukewarm water. Drain the excess water from the tray once the soil surface in the flat is moist.
Sow petunia seeds 1 inch apart in rows that are also spaced 1 inch apart. Place the seeds on the soil surface, then press them lightly into the soil with your fingers. Do not cover the seeds, as they require light in order to sprout.
Mist the soil surface with water to moisten it, then cover the flat with clear plastic wrap. Place the flat in a room whose ambient temperature is 75 to 80 degrees F in indirect light. Petunia sprouts in approximately seven to 10 days.
Remove the plastic once seedlings appear. Move the flat to a sunny window in a room whose ambient temperature is 60 to 65 degrees F. Water the potting mixture when the surface begins to dry, approximately every four to seven days.
Transplant the seedlings to individual seedling pots when they produce their third set of leaves. Plant one petunia seedling per pot at the same depth they were in the flat. Transplant the petunias to the garden once soil temperatures reach 60 degrees F and frost danger is past.