I received this question from a reader after my own heart:
"Hello Colleen. I started 11 different heirloom tomato varieties under fluorescent lights. All of the plants have at least two sets of leaves now, and I'm noticing roots coming out of the bottom of the plastic cell packs I planted them in. They look very spindly to me, like the stems are way too tall compared to tomato seedlings I'm seeing on different web sites and blogs. Is there anything I can do to make them less spindly?"
Thanks for the great question! Yes, there are a couple things you can do to make your tomatoes grow a little more stocky and less spindly. The first step, especially since you mention that the roots are coming out of the bottom of the pots, is to transplant them into larger containers.
If you're going from cells to a pot, I'd try to get 3.5 inch (roughly) pots. These are large enough that they will give the roots plenty of room to grow, but not too large for growing them under the lights (I know I run out of room under my lights very quickly!) You're going to bury as much of the stem as possible when you pot them up. Since yours are rather tall, I'd recommend placing the plant fairly low in the pot, so just the leaves are above the soil, filling the rest of the pot with either a peat/compost mix or a good quality organic potting soil.
There are two other things you can do to prevent leggy seedlings. First, keep your lights within 2 to 3 inches of the tops of the seedlings so they're not stretching toward the lights. The easiest way to do this is to suspend your lights from chains, which you can shorten as you need as the plants grow. Also, there is some evidence that either rubbing your hand across the foliage a couple of times per day or having an oscillating fan blowing air at the plants helps them grow sturdy stems.
I hope this helps! Thanks so much for the question!