A great way to feed your giant pumpkin plant is to foliar feed them. I believe that where foliar feeding can be the most beneficial is giving small quantities of fertilizers and nutrients where there might be minor (or major) deficiencies.
The leaves of a giant pumpkin plant can absorb many nutrients which can be quickly taken into the plant. Don't however believe all of the hype when it comes to foliar feeding your plants. I know the studies that are sometimes referenced when some companies are promoting their products and how much better foliar feeding is than any other method. The fact is that some of what the studies say are being stretched by the manufactures. The fact is that it really depends on what type of plant you are foliar feeding and what you are spraying that will determine the value. Also how often you foliar feed.
Like I mentioned before, some types of nutrients can't very easily enter through the leaf. Calcium is one of those. However, based on my leaf tissue tests, I think I may have that one figured out. My potassium in my soil is high. Potassium can block calcium from being taken up by the roots so based on that my calcium in the leaves should be a little low. However, my tissue tests actually had my calcium on the high side, so I believe the multi-mineral foliar applications of chelated calcium that is wrapped in an organic material is allowing the calcium to get into the plant. Now the question is can that calcium move to the pumpkin. That is somewhat of an unknown. However, if the leaves are loaded with calcium then in theory there should be lots of calcium available to go to the pumpkin. That is just a theory however.
I use a pump canister that is used for spraying stain to foliar feed my plants. They are exactly the same as the garden pumpkin canisters but cost a couple dollars less and are just a few isles away in the same Lowes or Home Depot. I'll usually add whatever I'm foliar feeding in relatively small quantities (1 or 2 tablespoons) to about 3 1/2 liters of water. Sometimes I'll add Yucca extract which is a non-ionic wetter to help the water stay on the leaves and not bead up and drip off. I'll then spray the tops and bottoms of the leaves as best I can until they are wet but not dripping wet. The stomata in a pumpkin plants leaves are larger on the underside of the leaves so try to get the bottom sprayed as best you can, but it isn't easy. Especially this time of year when the plants are large.
This evening I gave my plants 1 tablespoon of magnesium sulphate with one tablespoon of multi-mineral that was sprayed on both plants.