depends on strain too, ive heard some strains such as some blueberrys don't do well when topped.. generally i top first when there are at least 4 sets of nodes generally after one topping i get four tops in the main canopy, however this can be done again and again until you have a real bush going on! make sure you give the plant enough time to sort itself out before you put it into flower as it will be stressed (just had its head cut off!) generally you should look into topping if you have limited vertical space, also if your lighting is not that intense topping can make sure more bud sites get more light as there is an even top canopy not just a single cola sticking up..
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