Great article! I appreciate when alternatives are given to get to a goal...healthy seedlings in this case. But what I really wanted to comment on is education. Everyone should keep learning...boards like this, garden shows, new books on newer methods of gardening, what ever peaks your interest!
In my case, I have been gardening since I could walk (let's just say a very long time.) I have tried lots of things, some sucessful, some not so much. But the secret is to keep trying! Case in point. I have a bottom heat unit (your DIY version---rope lights between 2 plastic tubs...top tub filled with cell packs or with seed starter) and it makes a a great place to practice your clump transplanting, or to start individual plants. I transplanted tomatoes this year and placed them within 2" of my lights, adjusting them as they grew. But for some reason this year they got leggy. Now I know why. I had tomato and pepper seeds both and left the tomato seedlings waiting on the pepper seeds to sprout to transplant. Since they had overhead light as well, I didn't think it would harm anything, but thanks to your article on heating mats I think I have the answer!! Bottom heat after they sprouted! So you see, you should always keep reading, you never know if someone else has the answer you are searching for, and where you might find it!
Thanks for your articles, I really enjoy your style!
Bonnie aka:seeks roots