thanks man thats heaps good to know but by cutting the top half of the plant off it wont stress it out will it
sure as shit your gonna stress it, badly, that's okay. Your removing the head and torso of your plant practically speaking, waiting for it to re-route it's energy and continue it's flower developement with what the plant has left to work with. All energy is concentrated on bulking up and ripening the lower flowers over the time from when you take your first harvest. You won't have any issues if you clip it right, there is a way...
Double Harvests
Most marijuana plants take at least five months to reach maturity. Once the plant has reached maturity, it is forming its most potent marijuana, and should not be cut down completely. You can often induce the females to flower a second (and sometimes a third) time, especially if the plants are indoors or if the weather is expected to stay mild for several more weeks.
To encourage a second bloom, first take the bulk of the harvest: all but the smallest buds, and most of the leaf. Some green leaves should be left on the plant to maintain the plant's growth. After harvesting, give the plants a thorough watering, and water with a soluble, complete fertiliser that provides a good supply of both N and P. This will encourage new growth and continued flowering.
Indoors, the best procedure is to treat the plants like a hedge. Cut all the plants back to equal heights, about two to three feet tall. Remove most of the grass, but again leave a few green leaves on the plant. Don't remove lower branches even if they are leafless, since these will sprout again. Lower the light system to the tops of the plants, and maintain the daily cycle at about 12 hours. The second crop of buds will be ready for harvest in four to eight weeks. With this system, the plants appear like dense hedges of buds. If the second crop of buds forms quickly, you should try for a third crop. Continue to fertilise the plants regularly, and watch for signs of magnesium deficiencies, which often show up when the plants have been growing for an extended time.
Double and triple harvests are one of the benefits of indoor growing. Although plants are relatively small indoors, the original harvest of buds can be triples in the next four months.
~ BCbuddy