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How to Grow Vegetables in a Flat

By Jenny Harrington ; Updated September 21, 2017
Start vegetable seeds in flats indoors.

Starting vegetable seeds indoors allows you to get a head start on the gardening season. Depending on the type of vegetable, seeds are started four to eight weeks before they would normally be planted in the garden. They are then transplanted outdoors healthy and strong, making them better able to thrive in the more challenging outdoor conditions. Using flats, or seed-starting trays, to start your vegetables saves space as well as making it simpler to sow small, fine seeds, such as carrots.

Set the seed flat on top of a shallow tray, which will catch any water draining from the flat. Fill the flat with a moist, seed-starting potting mix to within ½ inch of the rim.

Make shallow, ¼ inch deep furrows in the soil with the eraser end of a pencil. Space the furrows two inches apart in the flat.

Sprinkle seeds in the furrows, following the spacing directions on the seed packet. Cover the seeds by filling the furrows back in with soil, then sprinkle water on the soil surface to moisten it.

Cover the flat with plastic and place it in a warm room to germinate. Most vegetable seeds germinate within seven to 14 days.

Remove the plastic once sprouts appear and place the flat in an area that receives at least eight hours of sunlight. Continue to water the soil as needed to keep the soil moist.

Thin the plants in the flat once they develop their second set of leaves. Pluck out the extra plants so each remaining seedling is two inches away from the next seedling.

Transplant the vegetables to a larger pot or to the garden bed once they have produced their fourth set of leaves. Cut the soil into squares with a sharp knife, so one seedling sits in each square. Plant the seedlings to the same depth in their new bed or pot that they were growing at in the flat.


Things You Will Need

  • Seed flat
  • Drip tray
  • Soil
  • Pencil
  • Plastic wrap
  • Knife


  • You can reuse flats from year to year; just rinse them in a diluted bleach solution to sterilize them.
  • Use aluminum baking pans or other shallow dishes as flats. Just poke some holes in the bottom for drainage.


  • Avoid over-watering the plants and make sure they receive enough sunlight. Fungus grows on soggy soil in low-light conditions and can quickly kill every plant in the flat.

About the Author


Jenny Harrington has been a freelance writer since 2006. Her published articles have appeared in various print and online publications. Previously, she owned her own business, selling handmade items online, wholesale and at crafts fairs. Harrington's specialties include small business information, crafting, decorating and gardening.