When I start Tomatoes I do it in a communal container that is about 4"x5"x2". When they have their first true leaves I transplant them into 16" drinking glasses that I've put holes in the bottom. I sink the seedlings into the soil less mix up to the leaves. Tomatoes grow roots all along the stem. I don't know of any other plant that does this. There they stay until planting out.

It does not hurt your plants to transplant more than once but you set your plants back a week or 2 every time you do.. That having been said it is better to transplant than have them in too small containers. Another year do it only once and save yourself the work of a lot of extra transplanting.

Yes sink the stem into the soil but don't do it too often or when you plant them outside. You don't want your tomatoes roots deep in the soil in cold ground. We do dig a bit deeper so we can make a water reservoir around each plant but the roots are not too deep.

here is one of my tomato seedlings,
and today one of my tomato seedlings seed leaf fell off
it was the size of the one in the picture

I think you may be watering it too much.

Yep, too much watering. Yellowing cotyledons is a sure sign. Even the true leaves are too pale.

And yes, for future reference it is fine, even good for them, to bury all the stem.

Dave

I never have any luck getting to the first true leaves with tomatos. What do you think I am doing wrong ?

Dowlinggram - I have seen you post the "it sets your plants back 2 weeks when you transplant" statement numerous times. - It simply isnt true.

Maybe if you are transplanting older plants and being really ham-handed with them. However if you are transplanting seedlings that are young, it maybe stalls their growth for 2 days. Yesterday I divided and potted up my tomatoes - they were 3-5 per 3oz cup, and are now all in individual 9oz cups. They were 2 weeks old with the second set of true leaves just emerging, and I know from past experience that they will be at least twice that size in another two weeks. I will move them into 16 or 20 oz cups in mid May, and plant them out June 1st. TIme and time again I have seen plants that I potted up grow faster and stronger than those I didnt get to for some reason. And starting them in bigger pots doesnt work for me either, as the soil stays to wet for the little guys and they drown.

Um, I also pot mine up several times, from tray, to modules, to 1litre pots - a gentle upturn of the damp pot or module - the little plantlets barely notice.
Otoh, tomatoes can and do get checked - mine go from a greenhouse in a sheltered home garden to a windy frost-pocket on my allotment - even with a long hardening time, a cold snap really can mess with them and not only set them back, it seems to lessen the overall vigour for the rest of the season........ so I don't transplant till really late (the 1litre pots).