Hi chlobell,

Answers to your questions:

"1. Should I cover them and turn the heat mat back on?" No, they don't need either.

"2. Our outdoor temperatures are warm now (70-80 degrees). Should I bring them outside for a few hours instead of letting them sit all day under the grow light?" Your temperatures are warm enough that you could start that now. Begin with a couple of hours in the shade then gradually increase the time, moving them into filtered sunlight and finally full sun.

"3. Given that it is warm enough to plant outside now, how big do they need to be before I put them in the ground." Most of the time we plant out when the tomatoes are at least 6-8" tall, but that is for tomatoes that are started indoors before it is safe to plant them out. I'd wait until they get at least two sets of true leaves.

Now I have a couple of questions for you:

What medium do you have them in now? Is it a soilless seed starting medium? It looks pretty wet to me, but I could be wrong. Are there drainage holes in the bottom of that container? If the growing medium is too wet, that could account for the slow growth, particularly if it is also a "heavy" mix.

We usually wait until we have true leaves before potting up, but that medium may not be the best for growing seedlings, so you might consider transplanting them into a standard growing medium (potting mix, not soil). If you do that, then wait 4-5 days before putting them outside.

I hope that helps.

Betsy

Here is a link that might be useful: Hardening Off and Physiological Changes

Thank you for your response! I had just watered them when I took that picture. Should I let them dry out completely before I water them again? Yes there are drainage holes in that container. The growing medium is Hydrofarm Jump Start Biodegradable pellets. I can see another set of leaves coming in on at least one of the plants so I'll take that as a good sign. Thanks for the help!