The two cotyledons (seed leaves) normally turn yellow and fall off. But if they are true leaves you are talking about then the most likely cause is excess water - either you are giving it too much or it isn't draining well and causing root rot. So let them dry out well before watering again. Stick your finger in as far as possible - if damp don't water.

If your soil mix has no added fertilizer in it then they will want a mild feeding of a well-diluted liquid fertilizer of some kind. Coir and mushroom compost have little or no nutrient value so some form of feeding is required. But they need to dry out some first. ;)

Dave

Thanks Dave,

Will let them dry out first before watering next time. Just a little nervous since never grew tomatoes from seed before.

The last time I grew from seed, lost everything to damping off. *You'd think I'd know not to over water. :o

La Donna

I started two different varities of tomatoes by seed they shot up in a covered seed tray. They grew so fast they were spindely. They got their second set of leaves and were transplanted. I put them on the porch for a few days and then in the sun, now they seem not to be growing. I did use a mild fish emulsion solution on them.