DRESDEN — Sienna Mazone was thrilled when her 65-pound white pumpkin won first prize in the Great Pumpkin Competition at the Common Ground Country Fair.

The 9-year-old is home schooled and helps with the family’s vegetable garden as part of her curriculum. Her science project was to grow a variety of pumpkin bred by Winslow-based Johnny’s Seeds called Polar Bear.

Sienna said she started the seed at the end of April in a greenhouse, then transplanted it into her family’s garden in June. She fertilized the seedling with organic goat manure and covered it with black mulch to suppress weeds and warm the soil.

As the plant grew and developed fruit, Sienna pulled all but one pumpkin off the vines to direct the plant’s energy into growing one, larger fruit.

As it expanded, the family decided to enter it in a contest.

“We were all excited that she won a blue ribbon,” said Sienna’s mom, Kimberly Mazone.

Ben Sturtevant, spokesman for Johnny’s Seeds, said Polar Bear is one of the company’s larger white-skinned pumpkins, capable of growing to between 40 and 65 pounds.

He said the variety is new and bred at the company’s trial farm in Albion by Rob Johnston Jr., the company founder and chairman.

“It’s one of our bigger jack-o’-lantern style pumpkins,” Sturtevant said. “It’s new to the 2011 catalog. It’s a brand new product and bred right here in Albion, so it’s an exclusive variety for us. We’re real proud of it. It really stands out in the crowd. You don’t see many big, white pumpkins.”

He said the company is so impressed with its size and beautiful white skin and uniformity that Sienna was asked if her prize-winning pumpkin could be showed off at agricultural trade shows in northern New England this winter.

Sienna gave the pumpkin to Johnny’s in exchange for photos of the pumpkin and a tour of the trial farm, Sturtevant said.

She also received 40 varieties of seeds for her garden next summer, including more Polar Bear seeds.

“We brought it from the fair to the corporate headquarters in Fairfield, and it took a couple of people to lift it it’s so big,” he said. “It’s one of a dozen Johnny’s bred pumpkins we have in our lineup. We have a pretty cool pumpkin breeding program and seed production facility here in Albion.”

Mechele Cooper — 621-5663

mcooper@centralmaine.com