DES MOINES

EARLY one morning about a month ago, Don Young peeled the floral bedsheets off the giant pumpkins growing in his backyard. Tiptoeing around the jungly vines, he carefully checked for holes. Then, bending his ear down over the nearest gourd, which was as high as his gut and wider than a truck tire, he gave it a solid smack and listened intently, like a doctor with a stethoscope.

“This one’s thumping pretty good,” he said with a grin.

Mr. Young is one of a number of amateur gardeners whose heart’s desire is to raise a pumpkin bigger than anybody else’s. These enthusiasts have always been obsessed, but now they are especially so. With the current world record at 1,810 pounds (a Smart car, by comparison, weighs 1,600 pounds), these growers can see the most important milestone of all on the horizon: the one-ton pumpkin. Galvanized by the prospect, they are doubling their efforts and devising a raft of new strategies involving natural growth hormones, double grafting and more, to become the first to reach that goal.

This fall’s pumpkin contests have begun, and as many as 14 amateur growers have won regional weigh-offs with entries tipping the scales at more than 1,500 pounds. The contests are far from over — they continue in force over the next two weekends — but already one pumpkin, raised by Dave Stelts of Edinburg, Pa., has come within three pounds of beating the 1,810-pound record set last year. Rumor has it that a record-breaker may emerge in California.

The extreme summer weather this year has somewhat dampened the prospects of many growers in the Midwest, including Mr. Young. Still, he plans to enter a couple of 1,300-pounders in a weigh-off in either Wisconsin or Minnesota this weekend, and true to his hobby’s compulsive form, even as he prepares for those contests he is busy mapping his strategies for next year.