MaXMaNanswered grow question 6 years ago I think the question "which week to switch to flower" is the wrong question to ask, as there is no definitive answer. I'd suggest that the most important issue when determining when to make the switch is (as other have suggested) the space you have to work with. Never plan for using all 8 feet of your grow height, and always account for roughly %50 more growth once you switch to flower. So, for example, if you want your final plant height to be roughly 6 feet, then switch to flower at 4 feet. Again, time it's self isn't a good determination of when to go into flower, but rather your particular conditions and goals. Also, it is good practice to give your plants 24-36 hours of dark when you do flip to flower, as it helps kick-start the process.