Why do some pumpkins grow to be so enormous?

• Rating

• pumpkin
• cinderella
• squashing
• heaviest
• biggest
• grows

The ball is where Cinderella needs to be. How do I get there on time? The magic happens when her fairy godmother waves her wand. A pumpkin nearby changes into a lovely carriage.

The fairy godmother isn't real, but huge pumpkins are. Atlantic giant pumpkins are the big ones you might see at your town's fall fair (Cucurbita maxima). Jessica Savage says that what we eat and carve is not the species. She studies plants at the University of Minnesota in Duluth, where she is a botanist.

The Atlantic giant is a huge one. Every year, people try to make the biggest thing they can. In 2016, a grower in Germany broke the record for the world's heaviest squash with a 1,190.49-kilogram squash (2,624.6 pounds). Some small cars weighed less than it.

Savage says that the most amazing thing is that pumpkins can even get that big. She became interested in a problem when she saw pictures of giant pumpkins at the Topsfield Fair in Topsfield, Massachusetts. A transport problem.

In order to grow, a pumpkin has to move water, sugar, and other nutrients. Pumpkins are fruits, yes. The roots need water to move up. Sugars that are made in the leaves by photosynthesis need to get to the fruit and roots. Plants use xylem and phloem to do this. Xylems are the tubes that move water from the roots to the stems, fruits, and leaves of a plant. The sugars in the leaves get to the fruit and roots through tubes called phloems.

Giant pumpkins need a lot of water and sugar, and they need it quickly. A typical giant pumpkin takes only 120 to 160 days to grow from a seed to a big orange squash. At its biggest, it gains 15 kilogrammes (33 pounds) of weight every day. That's like adding a 2-year-old child to its weight every day. Savage says that all of this mass must move through the stem. Most of the time, the stem is thin enough that you can still easily wrap your hands around it.

She asked giant pumpkin growers for small pieces of their competition fruits so she could study how the stems move so much food and water. She also took any pumpkins that exploded before the judges could look at them. She even got small pumpkins that farmers had turned down because they were too small before they grew. (Farmers will only let one pumpkin on each plant grow to full size so they can grow a big pumpkin.) She grew some of her own, too.

Savage looked closely at the pumpkins' stems, leaves, and pumpkins, and then he compared them to the stems, leaves, and pumpkins of other large squashes. She found that big pumpkins don't make more sugars. And neither their xylems nor their phloems work in a different way. The Titans just have more tissue that helps them move. "It's almost like the vascular tissue in the stem is growing in a mass," she says. The stem pumps more food and water into the fruit because it has more xylem and phloem. This leaves less for the rest of the plant.

Pumpkin or pancake?

The giant pumpkins in the contest aren't round like you might think. David Hu says, "They're not pretty." "They're too loose." Hu is a worker at Atlanta's Georgia Institute of Technology. He studies how things move and grow because he is a mechanical engineer.

As they grow bigger, giant pumpkins get flatter and flatter as they grow. Hu says that gravity just pulls them down. "They are stretchy. They have bounce. But as they get bigger and heavier, the spring isn't strong enough," he says. Pumpkins get crushed because they are too heavy. And if they get big enough, a small arch will grow under them. Hu says, "It looks like a small dome in the middle."

As a pumpkin gets bigger, the wall doesn't get much thicker. Hu says that a small pumpkin can hold up to 50 times its own weight without breaking. "But the big ones can't even hold their own weight," he says. "They can't do any more."

Hu made a model of how a giant pumpkin grows by taking samples of giant pumpkins and squashing normal-sized pumpkins to see how much weight they could hold. He says that a car big enough for Cinderella would never be a good car. Even if growers made giant pumpkins twice as heavy as they are now, the fruits would just get flatter.

Hu says of Cinderella, "She'd have to lie down." He also points out that her ride "wouldn't be very elegant." Also, the pumpkin would probably take a lot longer to grow. "If we wanted it to be eight times bigger," he says, "we would need an eight-year season."

Hu says that it wouldn't matter how tall a pumpkin was if you could grow it in space or under water. "In the end, all of the forces that flatten things are caused by [Earth's] gravity." In 2011, Hu and his coworkers wrote about their findings in the International Journal of Nonlinear Mechanics.

But Savage says that Cinderella might have had other ways to get around if a pumpkin carriage wasn't possible.

After all, you can hollow out giant pumpkins to make pretty good canoes. In fact, every year in Windsor, Canada, only giant pumpkins can enter a boat race. So, if the prince's castle has a moat, Cinderella might still be able to come out of a pumpkin.