Seeds Selecting a good genetic seed increases your chances in growing a large pumpkin. To get good seeds, join a local pumpkin grower association such as The Giant Vegetable Growers of Ontario,. Great seeds with proven histories of success are distributed annually to all club members free. Nursery store bought giant seeds are generally of low quality and will produce pumpkins under 400 pounds. With, proper care today’s modern seed stocks available from the GVGO have the capability to reach weights as high as 1800 pounds.