I start several seeds directly in 3.5" pots and do not pot up. I do, however, transplant about 1/3 of my seedlings to position them in the center if the pots, and this disturbs the roots just as potting up does. I have never observed any difference between the transplanted seedlings and those left undisturbed in the 30 years I have been doing this, but my experience seems to differ from that of others here.
I fertilize a couple of times with weak Miracle Grow liquid, and my plants are 10-12" tall after five weeks under lights.
TomNJ
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