same as any vegetable 16 hours on 8 off. keep the lights 1" above the plants. keep them watered when they dry out, those lights are warm but do not over do the water. i wait until the container is dry. also cut them when they get to 5" back down to 3" or they'll be leggy. as thick as a pencil may be too thick, too long to wait. mine are ~ 1/8" at the base when i plant out and they do fine. the key is to get them out as early as possible so they achieve max size prior to mid june when bulb formation starts. also onions do not require a lot of fertilizing so i fertilize just a few times before they go out.

tom

Thanks.I will cut back to 3 inches.I will fertilize lightly with kelp extract.I hope to have in ground by late march.

ohhhh, so I am supposed to trim down the green growth while they are under lights? That would explain why they did so poorly the last time, because I didn't know to trim them. Do the green parts, once trimmed, still grow properly once they are outdoors? And do I also do that with leeks started indoors, trim the tops to 3 inches? That would explain my previous failure.

megmaine.I trimmed the onions i planted a month ago, today to 3 inches.Some of the onions are getting multiple shoots from base.Yes, you trim them under lights as they will get leggy from artificial light and this thickens the shoots.I have grown leeks from seed for 10 years plus and do not trim at all.When they are 1/8 thick i plant in clump in garden and when they are pencil thick i seperate the individual leeks and plant 4 inches apart.I have been eating leeks continuosly threw winter, from may 28 outdoor planting in 2008.