Peanuts (Arachis hypogaea) are edible, annual legumes that are used to make cooking oil, which can be found in foods such as packaged baked goods and salad dressings. Many people also enjoy eating peanuts roasted in the shell, and although the shells are edible too, they are usually discarded. Instead of wasting those shells, put them to use in your garden by adding them to your compost pile.

Putting peanut shells in your compost pile keeps them out of the landfill, and they add carbon to your compost. Carbon is an energy source that nourishes microorganisms that break down compost materials, according to Washington State University. When there's not enough carbon in your compost pile, the materials in your heap won't break down as quickly, which can cause the microorganisms to die.

One drawback of putting peanut shells in your compost is that they break down slowly. That's thanks to their tightly intertwined cellulose tissues, according to Barbara Pleasant and Deborah L. Martin, authors of "The Complete Compost Gardening Guide." In fact, you might see peanut shells that you added to your compost pile in the spring still hanging around in the fall. This isn't necessarily a bad thing, however, because they will break down eventually and they do supply organic matter to the rest of your compost, Pleasant and Martin note.

Salted peanuts pose a problem when it comes to your compost. Too much salt will poison the microorganisms in your compost pile, Pleasant and Martin report. Before adding the peanut shells to the compost, rinse them thoroughly to wash the salt off the shells, Kelly Smith recommends in her book "How to Build, Maintain, and Use a Compost System." Soaking them will also help them decompose more quickly.

Though peanut shells can provide valuable nutrients to your compost heap, they can harbor fungal diseases and nematodes, which are pests that eat the roots of your plants, according to the University of Florida. If the shells are infected when you add them to your compost pile, the infection could be transferred to your plants when you layer the compost around them.