Ask Mr. Smarty Plants

We've never tried pumpkins before, either, but we understand most of the members of the Cucurbitaceae family can be very aggressive, sending vine tendrils everywhere. Since at the Lady Bird Johnson Wildflower Center we specialize in plants native to North America, we don't have much expertise in vegetables. Even those that are native to North America have been hybridized so much that they are no longer recognizable as native. That is the case with the pumpkin, so we won't have information on it in our Native Plant Database. But, we will go looking for some information that might help you produce pumpkins for your grandchildren.

From this Farm and Garden site, Growing Pumpkins, we extracted this quote on spacing when you are planting pumpkins:

"Grow pumpkins in a corner of the garden and train the vines to grow outside of the garden. Pumpkin vines are huge and they can take up most of your garden if you are not careful. Space plants 12"-18" apart. If growing pumpkins in a row, space the pumpkin plants at 18" in rows 6' apart. Alternately you can grow pumpkins on a hill of soil, compost or manure. When pumpkins are grown in hills make sure there is approximately 50-100 square feet of space per hill for the pumpkin vines to grow. Pumpkin hills should be approx 3' by 3'. Planting pumpkins on hills of rich soil or organic matter helps ensure these heavy feeders get what they need."

Obviously, it's already too late for that, but something to remember next year, when you plant pumpkins. Next we found this Yankee Halloween.com Growing your Halloween Pumpkin in which we found this suggestion: When the first baby pumpkins appear, select 2 on separate runners, and cut off all the rest. As new ones develop, cut those off also. This is to divert all the plant's energy into growing those pumpkins. Since you apparently only have the one vine, you might want to leave 3 or even 4 runners, each with its own baby pumpkin, for insurance. We couldn't find confirmation anywhere that it was okay to trim off other runners, but it would appear that would, again, divert more energy to the pumpkins you have left. This is not pruning so much as judiciously thinning. And, next time, leave WAY more room for those vines!