I love my heat mat, it seems to really help my tomato and pepper seed to germinate. But I've been reading lately that it can make tomato seedlings leggy. It sure dries out the cells fast also.
Thinking of maybe only using it on peppers next year, right now I mix my toms and peppers in a seed starting tray with separate cells.
As soon as I see the seedlings come up I'm torn of when to take the heat away. Right now I've got some habanero seed still not up, but I've already taken the heat away! Arrggg, thinking that next year I'll start my toms and peppers separately!
I always take the heat away when things germinate, I think if you do that then you won't run into problems with things being leggy (as long as you have the right amount of light for them). I also put a dome over top until the seeds germinate, that helps a lot with the drying out problem (but make sure you take it off when the seeds germinate, otherwise you can end up with fungus problems)
Definitely do pepper and tomato seeds in separate little seed starting containers... The peppers will love the heat, and I keep mine on the mats at least until they have their first true leaves and are ready to go into 2 inch pots. If you have room on your heat mat, they don't mind staying on the mat for a couple more weeks after being up-potted, either.
But I've noticed the same thing about tomatoes -- if you keep them on the heat mat even a day after you see the first seed germinate, you end up with leggy seedlings (no matter how close or how bright the light is). The heat mat shortens the germination time for tomato seeds by a couple of days, but they will germinate just fine without the heat mat (just keep them at indoor room temperature), and I don't know that I'll even put my tomato seeds on the heat mat at all this year.
So let's say after reading this, you've learned a valuable lesson...and you have leggy seedlings. Are they goners?
My tomato seedlings are btwn 1 1/4 to 2 inches tall with first leaves coming in.
My pepper seedlings are btwn 1 1/4 to 1 3/4 inches tall with first leaves coming in.
Marigolds are 1 1/2 inches tall with first leaves coming in.
Basil are 1 inch tall with no true leaves yet...?
All were sown same day...March 4.
Thanks for your input.
Pinger -- the marigolds & Tomatoes will both grow extra roots along the stem. When you go to prick & transplant them, plant them waaaay down there in extra-deep pots so the seed leaves are sitting on top of the soil line. I'm not sure about the basil & peppers, but I have been deep planting ALL my seedlings this year with very good luck (I just have't gotten to the basil yet and don't grow peppers.).
Get the lights on them ASAP -- it will help thicken the stems. Keep the lights very close to the tops of the seedlings -- I don't think any of the four you mention can have too much light, so even running them 20 or 24 hours a days won't be too much.
I keep things on a heat mat until I need the room for something else, or until they get transferred to such large pots that I can't afford the space. Petunias and impatiens have had heat for 4 weeks? 6 weeks? Begonias have been on the heat mat since early January. I bought my heat mat form the Park's 40% off sale last fall and wish I had bought 2 or 3!
Ping, just plant them deeply like Suzy said -- the basil too. I don't think that peppers will grow extra roots along the buried stem, but planting them deeper shouldn't hurt and will help them be stable in their new pots.
While the tomatoes might be leggy from being on the heat mat, the peppers and basils love bottom heat... so I am thinking that your seedlings are leggy because they aren't getting enough light.
I had some early tomato seedlings get leggy on me because I was germinating them upstairs by a window before I had my light shelves set up for the season... I just buried them as deeply as possible when I put them into their 2 inch pots, and they are already looking sturdier.
By the way, I just checked on my chile pepper trays and found that the seeds of nearly all varieties have just started to germinate -- a mere 5 days after sowing!! I know I've said it before, but my heat mats rock!!
My tomato seeds were beginning to sprout in about 42 hours after sowing... so keep a sharp eye on them if you put them on a heat mat (or just let them germinate at regular room temperature -- it'll only take a few days longer).