Answer: Petunia seeds take 10-21 days to germinate and should be started 6-8 weeks before planting outdoors. Your average last frost date is mid-May. If you allow 8 weeks for the seeds to develop into seedlings, with a target date of planting in warm soil towards the end of May, you should start your seeds indoors around the middle of March. If you start any sooner, the plants will become leggy and pot-bound before you can transplant them outdoors. Petunia seeds need light and warmth to germinate. Sow them on the surface of moistened seed starting mix and press them in with your hand. Place the trays or pots in a warm area, such as on top of the refrigerator, or on greenhouse propagating mats. As soon as the seeds sprout, place them under a source of bright light and keep the light on 12-14 hours each day, turning it off at night. Adjust the light source so it remains about six inches above the tops of the plants. Thin the seedlings by clipping the stems at soil surface, and keep the soil moist, but not soggy wet. By outdoor planting time, you should have some healthy, vigorous transplants.
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