How to Grow a Giant Pumpkin
good genetics. Buy the best giant pumpkin seed you can afford. The good ones are expensive!
Prepare the ground well. I started in March by making a mound of the best compost I could find. A whole barrell of kitchen compost, two bags of well rotted horse manure, a couple of bags of potting compost, several bags of lawn clippings... and leave them for weeks to settle down and relax before planting. This mound will ensure that the roots are well drained.
Have enough space for this giant plant to ramble. You probably need about 10 yards in each direction, that's 100 square yards!! When the pumpkins have set choose just one pumpkin to grow to be a giant and pinch out all the others, and pinch out the ends from all the side shoots. You want the plant to put all its energy into this one pumpkin and not into growing more green leaves.
bury some of the leaf joints with soil so that additional roots will make their way into the ground to bring up water and nutrients.
Feed and water regularly. The advice varies about how much to feed and water, but that depends on the weather. In hot weather it might need as much as 20 gallons a day. I make up a comfrey or nettle feed and use a couple of gallons of feed about 3 times a week. I might also use a high potash tomato food as a foliar feed. I have heard of people feeding beer to their pumpkins..what a waste of beer!
shade from hot sun if you can. If the skin ripens and hardens while it is still growing then it might split. Some people erect a little shade tent around the pumpkin. Here I have used a couple of layers of fleece but I might give it some more shade soon.
The other thing you need is lots and lots of bright sunshine and heat!.. Oh and some luck too!