Answer: Although it would seem that seeds should germinate and grow beautifully under greenhouse conditions, the fact of the matter is that your seedlings need a source of artificial light until they've developed 3-4 sets of true leaves. The tall, spindly and then floppy growth you describe is a classic symptom of too little light. Set up a corner in your greenhouse where you can provide supplemental light to your seedlings. I use fluorescent shop lights (two tubes per unit) and hang them from chains so I can move them up as the seedlings grow. Keep the lights only 3-4 inches from the tops of the plants (moving as the plants grow), and keep the lights on 12-14 hours a day. Be sure to turn them off at night -seedlings need time to rest.
I think you'll find a world of difference in the quality of your seedlings with this simple step.
Best wishes with your greenhouse adventure!
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