pumpkineer
n. A person who grows giant pumpkins, particularly ones meant to be entered in pumpkin-weighing contests.
Etymology
Examples
2002
Driving by in their cars in Cedar Valley, a small community north of Toronto, people will often slow down to take a look at the massive orange mound growing in Bach Bennett's yard. The really curious will stop and knock at the farmhouse and ask for a better look at the 650-pound (300-kilogram) pumpkin dominating the yard.

Bennett is always happy to oblige. He is not a farmer — he works as a designer and decorator in Toronto. But he is what he jokingly likes to call a pumpkineer.
—Rebecca Caldwell, “My, what a huge gourd,” The Globe and Mail, October 19, 2002
1988 (earliest)
In the World Pumpkin Confederation's [weigh-in] contestants compete with growers in Australia, New Zealand, Italy and the United States for prizes that can total $5,000. Last year's winner weighed in at 604.5 pounds, grown by a Vermont pumpkineer.
—John Spears, “Rival groups weigh in for gold in Nova Scotia pumpkin patch,” The Toronto Star, October 08, 1988
Notes
The first thing you need to know is that giant-pumpkin growing is a serious business. There's the grandly-named World Pumpkin Confederation; there are websites galore (BigPumpkins.com is good for general news, but big-time growers swear by the seeds found at Dill's Atlantic Giant); and there's even a book: How-to-Grow World Class Giant Pumpkins II. ("If you have ever dreamed of growing a giant pumpkin, then this book is for you.")

Then there's the money. Even small state fairs and pumpkin festivals award a few thousand dollars to the grower of the heaviest gourd. In Ontario, Canada, one of the world's best places to grow humongous pumpkins and the home of a large and dedicated patch of pumpkineers, the annual province-wide pumpkin fest comes with a first prize of CDN$15,000. The Guinness Book of World Records — who, you can just imagine, absolutely love this kind of thing — pay US$30,000 for a new pumpkin world record.

And it looks as though Guinness is going to have to pay up because the big-pumpkin world is still buzzing from the news of a new world record being set at the Topsfield (Massachussetts) Fair on October 5, 2002. The behemoth squash tipped the scales at a jaw-dropping 1337.6 pounds. That's a lot of pumpkin pie!