Actual plant size is IMHO less important than the maturity of the plant and whether it has as many branches as you would like.
If you are strapped for space, you can always bend, tie, or even remove branches.
The best time to initiate flower in a from-seed plant is when the nodes have gone alternating, signalling that the plant has reached sexual maturity. The top of the main stem will start to look a little zig-zag. This is when you can flower with least stress, and it will take very little time to show sex.
Clones my be flowered as soon as they have good roots.
stinkyattic Reviewed by stinkyattic on . when should i turn lights to 12/12 diff size plants hello every one please have patice with me i am new to all this. i have been searcing for good advice from smart people and this is the best site i have found. this is my first time growing and talking on line, so here's my guestion. i had 10 bubblious plants two died the eight left are all different sizes from one 20in,15in,15in15in,12in,12in7in,4in. they say to turn lights to 12 hous on and off at 18in.they sprouted 1 of april,so they are over two months old. i try to get pic. any advice my Rating: 5