Are peanut shells biodegradable? Can they be composted?

  • Date: May 14, 2022

Peanuts are one of the most popular nuts (or rather, legumes) in the U.S. According to the National Peanut Board, Americans each consume up to six pounds of peanut-containing items each year from confectionary to plain peanuts. Whilst peanut shells act as great protection for the peanut, we are often left with a pile of shells after our snack. These, unfortunately tend to end up in landfill via the trash.  But what is the alternative? Are peanut shells biodegradable and can we add them to our compost pile?

A bit of background – what are peanut shells made of?

Peanuts are actually a legume, rather than a nut, and come from the Arachis hypogaea plant. Interestingly, the plant flowers above grown whilst the peanuts, in their shells, grow underground.

During growth the energy-rich peanuts need to be protected from animals. This is where their shell comes into play. Although not the hardest shell around, the peanut shell is fairly tough and durable. Peanut shells are primarily made up of cellulose and lignin.

So, are peanut shells biodegradable?

When a material is referred to as biodegradable, it means that it can be broken down naturally by micro-organisms such as bacteria. Peanuts do, in fact, biodegrade. Although, they will take some time like other shells – most likely a couple of years rather than a couple of months.   But worst-case scenario, if they were to end up in landfill they would not exist there forevermore like some materials!

Can peanut shells be composted?

Composting is a wonderful way to get rid of waste whilst contributing to the health of your garden. Organic waste, anything from a cotton shirt to bamboo, can be diverted from landfill. Your garden and the plant will both benefit!

You may think that since peanut shells are biodegradable they automatically qualify to be added to your compost pile. Although a common misconception, this is not the case – not everything that is biodegradable is compostable. An item should only be composted if it will ultimately contribute to a nutrient-rich compost. Thankfully, peanut shells fall into this category.

Compost ingredients fall into two distinct categories – ‘brown’ and ‘green’ materials. ‘Brown’ refers to carbon-rich ingredients and include items such as twigs and dried leaves.  ‘Green’ composting items, on the other hand, are nitrogen-rich and include ingredients such as food scraps and freshly cut grass.

Peanut shells contribute to the brown part – they are rich in carbon. When adding anything to your compost pile, it is important to adhere as much as possible to the green to brown ingredient ratio suggested. Although composting can include a bit of trial and error – no two piles on the planet are the same – sticking to basic principles can vastly improve your chances of maintaining a healthy pile. If you are new to composting, you can find out more beginner’s info here.

Peanut shells also contribute to a healthy compost pile due to their aeration abilities. Like other shells, peanut shells do not easily compact. This ensures that air can easily flow throughout the pile. A heavily compacted compost pile can sometime leave no gaps for air to flow. This results in the microbes having very little or no oxygen to carry out their role in the process. Adding shells to the pile can help prevent this and promote a healthy, optimally functioning pile.  

Some considerations when composting peanut shells…

Southern blight should be considered when deciding whether to compost your peanut shells. It is fatal disease caused by the fungus Sclerotium rolfsii and it can cause chaos in your garden. Although most common in the southern states of the U.S., if the conditions are right it can also be found further north too.  If you live in these areas, it is perhaps best to avoid adding these to your compost heap. The last thing you want is a lethal fungal disease infiltrating an otherwise healthy pile.

As with other nuts, peanuts are often salted to make them more flavorful. Adding one or two salted shells to your compost pile is unlikely to pose any problems. However, larger amounts will need some extra preparation beforehand to ensure that too much salt does not enter the pile. Simply rinsing them in water will remove this unwanted salt.  

If you want to jumpstart the composting process you can crush up the peanut shells before adding them to the pile. Not the hardest shell to crack, a rolling pin or simply standing on them will do the trick. The microbes can get to work straight away and have a larger surface area to act on – gotta keep them happy!

The bottom line

Peanut shells are biodegradable and can be added to your compost pile – you may need some time and patience though! It will, however, divert them away from landfill whist also benefiting your garden. It’s a win-win! As with all nutshells, ensure that they are not coated in salt – or else you may do your garden more harm than good. You should also be aware of the Southern blight fungus if you live in certain regions. Although the composting process may kill the fungus, many consider it not worth the risk for minimal compost return.