Happy Halloween! Do giant pumpkins have a size limit?

Happy Halloween! Google commemorates Halloween with a massive-pumpkin-carving video. What's the science behind gargantuan gourds?

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    Leonardo Urena celebrates after his pumpkin won this year's Half Moon Bay giant pumpkin contest in Half Moon Bay, Calif., earlier this month. The pumpkin weighed 1,704 pounds, making it a new California record. The pumpkin's circumference was 195 inches.
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Google bid the Web-surfing masses a happy Halloween Monday with a time-lapse video of Googlers carving immense pumpkins in the middle of the company's Mountain View, Calif., campus. Each of the pumpkins weighs around 1,000 pounds., with the heaviest of them weighing in at 1,298 pounds.

Pumpkins are the world's largest fruit (botanically speaking, a fruit is any plant with the seeds on the inside), and they can get much bigger than the ones seen in Google's video. According to Guinness World's Records, the heaviest pumpkin ever, grown in 2010 by Chris Stevens of New Richmond, Wis., tipped the scales at 1,810.5 pounds.

Cinderella stories aside, titanic pumpkins are a relatively new phenomenon. In 1991, the world record holder was a mere 493.5 pounds. Ten years later, growers passed the thousand-pound milestone, and they've just kept getting bigger ever since.

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It all began with Nova Scotia grower Howard Dill, the most famous person in the world (at least when it comes to mammoth pumpkins). All of today's record-shattering fruits come from a single gourd from 1979 named the Atlantic Giant, a member of the subspecies Cucurbita maxima. C. maxima was first cultivated in the early 19th century, by growers who crossed a Japanese kabocha squash with a Hubbard squash.

In addition to the right seeds, there are a few other factors that go into colossal pumpkins. According to the National Gardening Association, the elephantine pumpkins prefer a soil pH of 6.5 to 7, with lots of organic matter. Giant pumpkins take 130 days to mature, and at their fastest rate they can gain up to 50 pounds a day, a rate comparable to that of the largest trees.

Why go to all the effort? Brobdingnagian pumpkins can be lucrative. As the NYU student-magazine Scienceline notes, California's Half Moon Bay Art and Pumpkin Festival paid the grower of the fair’s heaviest pumpkin $6 per pound.

If there is a theoretical upper limit to pumpkin size, science has yet to determine what it is. Writing in a 2010 article in the International Journal of Non-Linear Mechanics, a team of Georgia Tech researchers noted that, as pumpkins grow, they morph from spheres to pancakes. The team demonstrated that the flattening allows the pumpkins to distribute internal stresses so that they can grow to ginormous proportions without breaking. Put another way, pumpkins tend avoid cracking by growing only in the spots where they can do so without breaking.

The limiting factor here is gravity. But this could be overcome simply by constructing a hydroponic pumpkin patch aboard the International Space Station.

Okay, perhaps "simply" isn't the right word here. The costs to taxpayers would be enormous, as would the inconvenience to astronauts trying to maneuver around the rapidly expanding gourds. But wouldn't it be worth it so we could have a second moon?

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