syde00 is right, i recently had the same problem where i had 2 growing in the same very large pot. by the time of harvest one of them still looked like it was only 3 weeks into flower and yeld was non existant and the other plant looked as though it was only about 5 weeks into flower.
when they are all in the same pot you cant move them around or turn them to get more light as many people prefer to put the shorter plants in the middle to get more light. also if there is any problems with nutes or soil desease or bugs then all will probably suffer the same. i would never grow more than one in a single pot again its a lesson ive learnt the hard way.