If your seedlings are getting leggy, they’re not getting enough light. They are stretching up in search of more light, and the result is thin and weak stems. Generally, even a sunny south-facing window doesn’t provide enough light for most fast-growing annuals (although you can always try). What you really need to do is set up a fluorescent light with two bulbs in it- one warm and one cool to provide the broadest spectrum of light possible- and keep the lights only an inch or two above your seedlings. Other tips:
· If you covered your seedlings to keep them moist after planting, uncover them as soon as they have germinated. An environment that is too moist may cause damping off, where the seedlings basically rot at their base, fall over and die.
· Thin the seedlings so that there is space between each individual one. Seedlings that grow too close together will depend on each other for support, and end up with weak stems.
· Turn an electric fan on your seedlings for at least a couple hours per day. Some air movement will also help to strengthen the stems and prevent mold and mildew from forming.
Why reinvent the wheel? More seed-starting tips can be found here: