Start petunia seeds indoors eight to 12 weeks before the last expected frost. Sow seed on the surface of seed starter in trays or cells. Do not cover the seeds.
Water to thoroughly moisten the soil and cover with clear plastic to increase the humidity level.
Place in an area that receives direct or bright filtered light. Petunia seeds require light to germinate.
Mist daily to keep the soil moist and do not allow it to dry out. Germination will occur in seven to 21 days depending on the soil temperature and the species.
Remove plastic once seedlings emerge and place in sunny location. Keep soil moist.
Transplant to individual pots when seedlings have their second set of leaves--approximately two to three weeks.
Plant seedlings outdoors once the danger of frost has passed and temperatures remain above 50 degrees.