You want to wait until they get at least 4-5 sets of true leaves before they can go into rows in the garden.. Mine go about 1" apart in rows 4-6" apart. I do zigzag them qa bity in the row so that each one has enough room to grow. In the cobweb rows you can go a bit closer although they tend to clump up quickly too.
What I do is to try to tease out group of the seedlings with the soil still attached and then make rows out of them, separating them gently. It is definitely one of those NO COFFEE exercises as you want to have a STEADY HAND. I always leave a bit of the potting soil as I transfer to the row. That seems to cut down on transplant shock. If you can do the process in a light rain it works even better although my neighbors I'm sure have thought "too stupid to come in from the rain". You see what I do for the semps??
If you have the room you can do this process in stages, transferring groups of small seedlings to new pots and then allow those to grow to a size that you can plant outdoors in specially prepared beds. With VERY high densities of seedlings, that might be the only plan.
Now you see why Ed Skrocki raising 20K seedlings each year was so impressive!
Kevin
