Why are my tomato seedlings turning yellow?

I'm sure this question has probably been asked many times, but I'm new here - and relatively new to gardening - and don't know how to look it up!
Boy, this site is HUGE! LOL!

Could be many things. What's your setup? Lights or windows? What type of growing medium/potting soil and fertilizer? How many weeks ago did you plant them?

A picture would help, if you've got one. We always enjoy looking at pictures of seedlings! :o)

Could be too much fertilizer/not enough. It's hard to tell without knowing more. And honestly, I had the same problem with mine and it took me some time to figure it out. We'll get you headed in the right direction, though.

Thanks dividedsky!

Well, I planted them at the beginning of April. I planted them in small peat pots in a mixture of potting mix and one of those bricks that you add water to and it expands. (can't remember what it's called - but it's made by Burpee). I've watered them everyday - or when they felt somewhat dry, at least. I might have overwatered. And I have to admit that I haven't added any fertilizer, though I do have some Miracle Gro for tomatoes. Should I add some of that? I'll try to post a picture, if I figure out how! (and if I'm not too embarrassed)!

No need to be embarrassed. I finally got 8 beautiful trays of seedlings last year after much failure, and felt a little like an expert. Then all but killed my tomato seedlings this year with a bit of an accident. It happens.

They might need 1/4 to 1/2 strength miracle grow - once a week? Someone else should chime in on this one. Sounds like they might be a little hungry. Not too much, though, or you'll burn them.

The bricks are coconut coir? Love that stuff.

I looked up the coir pellets on Burpee's web site and the description did not mention "fertilizer" so I'm assuming that's why your seedlings are yellowing.

I agree with dividedsky - use 1/4 to 1/2 strength to start out with.

http://www.burpee.com/product/seed+starting/coir+pellets+-+48+pellets.do?search=basic&keyword=coir&sortby=newArrivals&page=1#reviews

They might be turning yellow because they're getting too much water - tomatoes do that. I'm having the same problem now because of 3 days of thunderstorms and heavy rain. My garden is saturated, and the tomato plants are turning yellow. They'll be OK again, though, when the garden dries out.

Water your plants from the bottom. Wait until potting mix looks a little dry on top, then just set your cups in a container with about a half inch of water. It will take a while but when the top looks moist, take them out. I mix just a little miracle grow in the water. Just enough to give it a slightly blue tint.

OK, I admit that I have been watering them quite a bit. Also, I finally put fertilizer on the yesterday and we'll see how they do. I didn't know that over-watering would do that! I'm learning. I just hope I don't kill the poor things!

When I'm rearing seedlings, I check them morning and evenings - the grow light is in the same room with the computer, so it's easy to do (and easy to remember to do). One indicator I use is how heavy a seedling / pot feels. If it feels "light", it's definitely time for water. If it feels "normally" heavy, I wait a half day & check again. I'd guess I average about 36 hours between watering. The seedlings are in peat.