When pumpkins are sent to landfill, they release methane, a potent greenhouse gas that, over a 20 year period, is around 80 times more powerful at trapping heat in the atmosphere when compared to carbon dioxide. 

The lack of oxygen in landfills causes pumpkins to rot “anaerobically,” which releases methane. They are alsofull of water, and when they mix with waste and moisture it creates leachate, a toxic sludge that can pollute the environment. 

Though a single pumpkin might not do much damage, if you consider how many pumpkins are trashed each autumn, it adds up. 

“Maybe if we had a handful of pumpkins going into that waste stream, that might be one thing,” says Chris Enroth, horticulture educator with the University of of Illinois Extension, which organizes annual “Pumpkin Smash” events to help people recycle and compost old jack-o'-lanterns and pumpkins. “But we have millions of people who buy multiple pumpkins. We're talking about hundreds of millions of pumpkins that need to be disposed of post Halloween, and it's just a massive amount of organic material that goes into the landfill system.”