When to go from 18/6 to 12/12?

[turtle420]

I've always just used the old double the size measurement. Once put into flowering it normally doubles in height.

I.e. If its 2 feet tall after 6 weeks of veg and then put into flower it should roughly only grow to around 4 foot.

Definitely... I'm on my 1st grow, so I don't have that much experience, but the general number I've seen is that the plant will grow from 2 to 3 times its veg height. So carefull you don't end up with a tree...