Most varieties of seeds require warm, moist soil in order to germinate. Even if you start your seeds indoors, the soil temperature may be cooler than the ideal germination temperature for your plants. Germinating seeds with the help of a heat mat gives you control over the soil temperature and gives your seeds the best change of successfully sprouting.
Begin your seeds indoors based on their particular germination times. Seeds should be started anywhere from three to 15 weeks prior to the last frost of the season.
Plant your seeds according to the package directions of each variety. A good rule of thumb is to plant four times as deep as the width of the seed. Sow in a planting tray and a soilless seed-starting mixture. This will help maintain adequate moisture during germination and prevent soil-borne diseases.
Place your seed tray on your heat mat. Set the temperature to the ideal germination level for the variety of seeds you planted. Plant varieties with similar germination temperatures together in the same tray.
Moisten the potting mix regularly with a spray bottle at the lightest setting. Fertilize your seedlings with an all-purpose liquid fertilizer diluted to one-quarter strength.
Remove seedlings from the heat mat two weeks before you plant to transplant them to the garden. Gradually acclimate your plants to outside temperatures and conditions by placing them outside during the day for several days prior to planting.