Actually, I can't claim credit for this as my tomato trick, I learned it from Fran on the winter sowing forum at GardenWeb. I used to live one town away from Fran when I lived in Massachusetts, and sometimes we would coordinate our winter sowing efforts. She would sow tomatoes and if I had seeds she liked, I would sow extra of those for her. Anyway, this is what I do with my tiny tomato seedlings, and I learned it from Fran.
Often tomatoes grow very leggy, no matter how much light you put them under, or how close you set it. This is how I deal with that legginess.
First, I start them in only one inch of moist soil. Once they've sprouted, and are starting to show their first true leaves, instead of potting them up, I just add soil to the cup that I started them in. The tomato stalk will root in the new soil all along its length.
I hold it very gently by its seed leaves, and then very carefully spoon loose soil all around the stalk. It's important to be gentle, because if the stalk breaks it's a goner. Then I spray it with water on top to clean some of the soil off the leaves, and set it in a few inches of water, until the new soil has drawn water up into the cup.
About a week later, I give them all a nice drink of fish emulsion (actually, Fran doesn't use fish emulsion, I added that part because I prefer keeping the seedlings organic). I keep an eye on them to make sure the soil doesn't dry out.
The ones in these photos were topped up with soil on February 18. Today they look like this:
I plan to leave them in these cups until I set them out at the beginning of April. I'll give them another couple of drinks of fish emulsion, and probably some seaweed extract too.
And when I set them out in the garden, I will dig an extra deep hole, strip off some of the leaves, and set as much of the stalk as possible into the hole, so it can continue to root.
This trick works really well for me. Now, if the weather here would only cooperate and give us some heat this summer, I will be happy.