I have a small bed of mixed greens I am growing from seed next to the only south-facing window we have. They shot up quickly, but now I am concerned that they are shooting up too quickly. The seedlings are all about 2 inches high now, with only one set of small leaves. They are spindly and seem to place all of their energy into growing taller, instead of producing leaves. I am not able to place them outside, so I am wondering if anyone knows why this is happening, and if there is anything I can do.
From my basic understanding, as it may still be early in the season, and as the sunlight is less intense, they may be "reaching". It's pretty normal if you ask me. Most of their energy has been spend on root development, and now it sounds like they are just starting to photosynthesize. Couple inches from the base of the plant to the first nodes are typical in seedlings, depending of variety, from my experience. I honestly wouldn't worry about it much, once they put on their 3-4th leaf sets you can give them some food, unless it's already in the soil. For my window sill herbs, I like to turn the pots 1/4 of the way aorund a 360 degree axis every couple of days for good light distribution. A little compost topdressing usually straightens things out for me, as well. Hope this helps.
You might find a south-facing window too warm - lettuces will bolt (go to seed) and over-grow if they are too hot. They are also more likely to become bitter. Lettuces won't even germinate over 25 C/77 F. They might actually do better on a cooler windowsill.
I realise your post has been up a while so you may be quite far on with your plants now. It's true they do "reach up" early on, especially if closely-planted, but you can "cut and come again" for small, tender salad greens rather than waiting to pick whole lettuces - this way they have no chance to bolt and they re-grow nice fresh little leaves.
Ah... lettuce. Yum.
With greetings from Britain
It's fun to be me, and still legal in 9 states! Wanna see my tiny ad?