. I generally leave seedlings in their 6-packs
until the pots are almost filled with roots. This prevents one type of
problem: Soil ball falling apart when you take it out of the pot, which puts
mechanical stress on the roots, and sometimes the stem, if it's delicate
enough. This may not be the best solution, but the opposite's a mess: Losing
80% of the soil and having to handle the roots too much.

One problem is that the plants seem to go into a 'hold state' and grow very

slowly after they reach about one inch high. I'm not sure what is stunting
their
growth, but I'm reluctant to move them outside when they are that small.