I went by Northwest Seed and Pet and chatted with the sales associate about growing giant pumpkins. He used to grow giant hubbard squash so he had some tips for me. Heat in the soil is key for squash to grow rapidly and while I've considered buying a heating cable and putting in the soil underneath the pumpkin, that seems to take some of the sport out of it. He explained that he used to take gallon milk jugs, paint them black, fill them with water and bury them half way in the soil 6 inches to the north of where he plants the squash. The jugs harvest the heat from the days sun and hold it overnight. You might think a short growing season is our main gardening problem in the Spokane area. It's actually the cold nights. The soil cools down and slows the growth and delays the ripening. Holding heat int he soil overnight is key to ripening. That's why people shouldn't curse all those round rocks in the Valley. They essentially do what the milk jugs do in holding heat overnight. Another technique I've heard of is to bury fresh manure under two feet of soil and it will heat the soil above as it composts.
Speaking of manure, another key to pumpkin growth is calcium. I guess that's why people are said to pour milk on their pumpkin, even inject it in to the stem. It's a good source of calcium. The sales associate put me onto an organic source of trace minerals including calcium - fossilized dinosaur poop or more properly known as coprolites. So I've got my bag of coprolites and I'll amend that in the soil. It's cheap too, about $4. The kids are going to get a kick out of it too.