(Inside Science TV) -- About 100 million Americans drink coffee every day. The average coffee drinker will spend about $165 each year on the beverage. This means a lot of leftover coffee grounds.
Students at Arizona State University in Tempe found a use for the used grounds.
"[The] Grounds for Grounds program is a recycling program that we started to recycle Starbucks coffee grounds on campus and use them in our flower beds and our lawns, and even sometimes in pest control," said Vicente Solis, a civil engineering student at Arizona State.
Solis and fellow student Rigoberto Polanco collect more than 500 pounds of used coffee grounds each week to use as a natural fertilizer.
"We usually just throw straight coffee grounds on the lawns. For our flower beds, we mix [the grounds] with a little bit of compost, like a 50-50 mixture," said Solis.
The results they've seen are healthier flowers and plants, and greener grass.
When spread over flower beds and lawns, coffee grounds slowly release nitrogen -- a key nutrient that helps plants grow -- into the soil. The used grounds also attract earthworms. As the earthworms dig in the soil, the amount of water and air allowed to flow through the soil increases. Earthworms also break down organic matter in the soil like leaves.
Using coffee grounds as natural fertilizer can also save money on lawn and garden care.
"You can use coffee grounds on your flower beds and on your lawns instead of going out and buying synthetic fertilizer," explained Solis.
Used coffee grounds are easy to come by even for those who don't brew coffee at home.
"They can go up to any Starbucks they want and ask for coffee grounds," said Solis.