How to Start Plant Seeds Under a Light With a Heat Mat


Starting seeds indoor in early spring allows your plants time to grow strong and healthy before being transplanted outside. Indoor conditions often don't meet the requirements for healthy plant growth on their own. Supplying bottom heat to the soil and using grow lights helps provide the proper temperature and light requirements for your plants. Soil maybe up to 5 degrees cooler than the room temperature, and light from a window is rarely sufficient. Providing proper heat and light takes little additional effort and is worth it.

Step 1

Fill seed starting pots or trays with a quality potting mix. Moisten the mix thoroughly and evenly with water before sowing the seeds.

Step 2

Sow two seeds per pot or space seeds 3 inches apart in trays. Sow seeds to the depth recommended on the seed envelope and then moisten the soil surface.

Step 3

Place a plastic bag over the pot or tray to hold in moisture during germination. Set the pots on top of a seedling heat mat then plug it in and turn it on. Maintain a temperature of 70 to 75 F during germination.

Step 4

Remove the plastic bag once seedlings emerge. Set an adjustable grow light over the pots, adjusting it until the light is 3 inches above the top of the seedlings. Leave the light on for 12 to 14 hours a day, turning it off at night.

Step 5

Adjust the temperature of the mat down to 65 F after germination. Provide enough water to keep the soil mix moist but not soaking wet.

Step 6

Adjust the lights to maintain the 3-inch space between it and the seedlings as they grow. Avoid letting the top of the plants touch the bulb as this may burn them.

Tips and Warnings

  • Always provide enough light and heat. Too little causes the seedlings to dampen off and die.

Things You'll Need

  • Pots
  • Potting mix
  • Plastic bag
  • Seed heat mat
  • Grow lights


  • University of Minnesota Extension:Starting Seeds Indoors
Keywords: grow lights, seed heat mats, starting seeds indoors

About this Author

Jenny Harrington is a freelance writer of more than five years' experience. Her work has appeared in "Dollar Stretcher" and various blogs. Previously, she owned her own business for four years, selling handmade items online, wholesale and via the crafts fair circuit. Her specialties are small business, crafting, decorating and gardening.