Bottom heat is normally the most critical factor. It is also important to make sure the seeds get sufficient moisture, but never let them stand in water. Be sure to read the package, since some seeds germinate best in light and should not be covered with soil. Speaking of soil, a good potting or seed starter mix purchased from a nursery works well, or you can make your own by combining sand, peat moss and vermiculite or pearlite. Once the seeds germinate, move them immediately to a sunny location to prevent leggy plants, Goodspeed says.
Most homes are too dark and too warm at night.
A small cold frame next to the house, a hobby greenhouse or sunroom that can be cooled down are usually better than a warm, south-facing room in the house. After the seedlings begin to grow and produce their first couple of true leaves, transplant them from the seeding flat into individual pots or small packs, he says. When transplanting, be careful not to disturb the roots any more than necessary. Use a dull table knife to separate the plants and support the roots as you move them to the new containers. Another precaution is to make sure that the new container's soil drains well.