By waiting for the right thermal window, you ensure your petunias spend their energy on blooming rather than just trying to survive. To give you the best advice, could you tell me: What or State are you in? Are you planting in containers or in the ground ?
Growing petunias from seed is rewarding and cost-effective, but it requires a mastery of the calendar. Petunia seeds are tiny (almost dust-like) and need a long lead time to reach blooming size.
If you plant them too early, your season is over before it begins. If you plant them too late, you miss weeks of blooms. Here is your definitive guide on when to plant petunias to ensure a show-stopping display. when to plant petunias
A petunia planted in warm soil in May will often outgrow one planted in cold soil in April.
Seedlings need a bright light source and steady warmth to prevent them from becoming "leggy." By waiting for the right thermal window, you
If you wait until May to sow petunia seeds directly into the garden, you likely won't see flowers until late summer, missing the prime gardening season.
Before moving indoor-grown plants directly into the sun, place them outside in a shaded, sheltered spot for a few hours a day, gradually increasing their exposure over a week. Growing petunias from seed is rewarding and cost-effective,
Nighttime temperatures are more important than daytime highs for young plants.