[dmforcier]

Depends on how deep the containers are. I would want to transplant before the roots become too bound, and the deeper the soil in the cup the longer the plant can go before getting there.

In order to keep the root ball coherent, I make sure it is nice and moist before moving it. then water in pretty well. If you are careful there should be very little shock from the transplant itself. Thing is, people put the new pot in different surrounding conditions, e.g. sun instead of artificial light, or outside to wind, and this can cause a modicum of shock.