Different strains have different rates of growth. For example.. The first grow I ever did was Haze and Kush. The Kush grew small dense nugs and yielded about 2 zips...The haze however grew bottle sized colas and yielded around 3 zips. It all depends on the strain. If they were in two different environments or different nute schedules that would be different but I take it that's not the case.