Supersizing pumpkins

Engineers model extreme growth in fruits

Linus was right after all. Not only does the Great Pumpkin exist, but scientists have figured out how he manages to get so big.

In a sort of self-perpetuating cycle, the bigger a gourd gets the more physical stress it experiences — thus triggering giant pumpkins to grow even more.

“Their weight generates tension, which pulls cells apart and accelerates growth,” says David Hu, a mechanical engineer at the Georgia Institute of Technology in Atlanta whose team has submitted a paper to a peer-reviewed journal.

Chris Stevens’ record-breaking pumpkin weighs 1,810.5 pounds, shown here with New York Botanical Garden staff. Scientists now think they understand how pumpkins like this one can grow to enormous sizes without splitting apart.
Chris Stevens’ record-breaking pumpkin weighs 1,810.5 pounds, shown here with New York Botanical Garden staff. Scientists now think they understand how pumpkins like this one can grow to enormous sizes without splitting apart. Credit: The New York Botanical Garden
Such research doesn’t just illuminate the story behind record-setting pumpkins, like the nearly 1,811-pound behemoth recognized this month by Guinness World Records. The work also addresses larger questions of plant development, such as how tissues cope under stress, Hu says.

All giant pumpkins are grown from a single strain, the Atlantic Giant seed, which has a longer growing season than normal pumpkins. The fruits start out round, but once they get to about 220 pounds they begin to flatten under their own weight, eventually resembling a giant deflated sack.

Wondering how the monsters got so large without splitting, Hu’s group squashed regular-sized gourds in the lab see how much stress they could take before rupturing. The researchers then created a mathematical model of how the fruits could accommodate the stress. 


Smashing pumpkins from Science News on Vimeo.
Pumpkins can take only so much stress before splitting. Some kind of internal coping mechanism must allow pumpkins to grow to humongous sizes, scientists say. Credit: David Hu/Georgia Tech


The model predictions matched observations of giant pumpkin dimensions sent in by 50 farmers from around the country. Hu says that plastic, or irreversible, deformation allows the fruit to distribute stresses so it can grow — sometimes adding 50 pounds a day — without breaking.

The New York Botanical Garden, where the world’s biggest pumpkin will be carved this weekend, says that a 2,000-pound pumpkin could be grown within the next few years.

Pumpkin squash from Science News on Vimeo. Scientists have found that as a giant pumpkin grows its weight distributes higher stress in certain areas (red), triggering more cell growth there and giving the gourd a flattened shape. Credit: David Hu/Georgia Tech

Alexandra Witze is a contributing correspondent for Science News. Based in Boulder, Colo., Witze specializes in earth, planetary and astronomical sciences.

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