how tall until i flower?

wondering how tall i can let my plants get before i flower them. im using 4 inch sure to grow cubes.

i have an ebb and flow set up, my cieling space is unlimited, my temps are perfect.
i have 400 w mh light, going to switch over to hps when i flower.

but i really would like to know the max height i can start to flower them at before they get too big.. cause i can only get one grow in for the next 4 months.

im a first time grower, i really need the info

thanks everyone

depends on the strain. get a taller variety. grow it for a month and a half or two. it should be around 3-4 feet. then flower it. It will grow probably another foot or two. some may grow even more. do the research on the strain.

i have northern lights they are already 10 inches tall, 3 or 4 ft sounds great to me!! but 4 in grow cubes can sustain those beasts?