Answer: There are a couple of reasons I can think of for why your pumpkins would slow down and stop growing. The first is lack of water; pumpkins are water hogs because about 90% of the pumkin is actually water. Another is lack of nutrients; since they grew in the same place last year they may have depleted the soil in that spot. Third is that some disease has actually attacked; pumpkins are subject to a number of foliar problems which cause the leaves to shrivel; finally, perhaps you are growing an extra-early-maturing variety? (The normal range is 90 to 120 days with the approximate timing listed on the seed package or label.)
In any case, leave them on the vine as long as possible and do your best to cure them as well as you can to try to increase their storage time; depending on the variety and curing and storage conditions, some can be held for up to a year.
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