Take Chelle's advise. The purple color that is so dominant on the back side of the leaves is showing you a phosphorus deficiency. Other nutrient deficiencies are probable. Even if you have enough phosphorus in your soil, cold or alkaline soils disallow the uptake. If you do the compost/manure or for that matter any other solid-matter-type fertilizer you will be waiting so long that we'll be harvesting pumpkins before you have any effect. Go with the water soluble. I really like the Dr Earth liquid fertilizers. (like the Organic All Purpose has fish, kelp and molasses) Nice quick response. Later you can go back and fix the soil for future plantings.
(Cottonseed meal is a nice slow pH reducing fertilizer) For now you need something quick.
