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How to Plant Petunia Seeds

By Amma Marfo ; Updated September 21, 2017

The petunia is a delicate looking, yet hardy warm-weather annual that is typically grown in planters, flower beds, as borders to yards, or from hanging pots. With their flowers’ trumpet like shape, petunias resemble the climbing morning glory, but show off in more of a bush-like appearance. Once your seeds are grown, and seedlings planted outdoors, you can enjoy the attractive multicolored showings of pink, purple and white petunias in bloom throughout the summer.

Place your pots in the seed tray and fill them with soil. Set the tray under a grow light or in a sunny window.

Sprinkle the petunia seeds over the top of the soil 10 to 12 weeks before the last spring frost for your area. Don’t bury the seeds in the soil or cover them, simply press gently to ensure they are in contact with the soil.

Fill the bottom inch of the tray with water and give the pots time to absorb it. Refill the tray as needed to water the pots, but do not allow the pots to sit in standing water for more than an hour before you pour off any excess.

Cover the tray to let the seeds germinate. Continue to monitor growth and water as needed. Once the seedlings have sprouted, remove the lid and tend to the seedlings until your region has passed the frost free date.

Harden off your plants by setting the petunias outdoors during the day but shielded from any direct sunlight or wind. After doing this for a week, the seedlings should be strong enough to handle outdoor planting in areas which receive full sun.


Things You Will Need

  • Seed tray and lid
  • Small seedling pots
  • Potting soil or seed starter mix
  • Grow light, optional
  • Petunia seeds
  • Water


  • Maintain your outdoor plants over the summer by cutting back half the growth of plants which look scraggly, followed by good watering and feeding. Often pinching off the growth tips of the petunias when they are young will encourage the plant to branch and form a denser, bushier shape.


  • Be sure to keep the soil in your pots moist, but not dripping with water when picked up. A dry seedling will die of thirst, while an overly wet seedling can die of disease. Monitoring your soil moisture daily will help you keep a keen eye on your plants.