I have used heating mats for years and last year my friend, a new gardener, bought a heating mat for starting her seeds. Many things grew well but she complained to me that none of her snapdragons had sprouted. The seeds were bought from the same seed company so she couldn't figure out why none had come up.

I asked if she had put them on the heating mat and she had. That's why none sprouted I said. Snapdragons do not require bottom heat. The germination temperature is cool at 65 degrees and the mat raises the temperature too high so you cooked your seed.

My advice to newbie gardeners is that when you are using a heating mat pay attention to the germinating temperature on the seed package. With some plants a heating mat is beneficial and to others it is a detriment.