Thanks! How long can they veg in the 4 inch rockwool cubes before I need to transplant them? If I'm keeping the cubes watered but the roots are growing out of the bottom of the cubes and dying, does this hurt the plant?
depends, but in general; no, not really.... I've had plants in hydroton, rockwool and perlite with roots coming out the bottom all the time...in fact if I didn't see roots I'd suspect something was wrong////
now granted, this all supposes you are on some sort of timed watering/feeding schedule (manual or auto) and your roots won't be dry for hours on end....
....as far as how long/big the plants get in 4" cubes: I'm pretty sure they can get as big as practical before tipping over, et...although the limit of all this is how much ANY medium can remain moist in relation to the water/nutrient
transpiration rate of the plants foliage mass & surface volume... in other words a 4" rockwool cubes moisture will be used up pretty fast with a big plant, thereby the roots sticking out of it will be doing most of the uptake....I mean gheez, this is sort of a common sense call, esp w/o references or pics...
I'm thinking 2 weeks or 8-12" tall max (not topped) with all things being avg/equal (this is w/o knowing if your plants are in trays, or whatever other environmental variables are in play)