I just got a warming mat for germinating seeds. I put it under a grow light and everything seemed okay, but then my seedlings directly under the light died. The ones on the edge are seem fine though. What happened?
A warming mat is great for getting seeds started, but remember that higher soil temps mean that plants will dry out faster than they might otherwise. Also, fluorescent grow lights produce enough heat to dry out the soil and kill your plants. Keep seedlings moist, but not wet. Fill a clean spray bottle with water and let it sit at room temperature. Don't water your plants with cold water.
As your plants get their true leaves and the season progresses, cut down the number of hours per day that you are using the mat. Adjust watering accordingly.