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You've already got your

You've already got your pumpkins off to a good start by applying higher concentrations of Nitrogen (but not too much) in the early growth stage. Before starting fertilizer, I hope your soil was prepared with generous amounts of organic matter such as manure and compost as pumpkins are big feeders.

Switch to a formula higher in phosphorus when the flowers appear--and through the flowering and fruit stage--such as 5-10-5 or 5-15-5.

After fruit set, you can add more potassium for fruit growth. Either switch to a higher potassium formula or just supplement your 5-10-5 or 5-15-5 with extra potassium.