Yes! You Can Compost Shrimp Shells! – Find Why It’s Good!


Shrimp shells can be composted in regular backyard compost piles or bins. They are rich in Nitrogen, and should be considered a green material. In addition to being quick to decompose, the materials that make up shrimp shells also have antifungal properties, as well as other metabolic benefits to plants.

But we don’t need to stop with just shrimp shells and shrimp tails! Lobster, crab, mussel, prawn, clam, and even oysters shells can all be broken down in a compost pile. Even if you don’t have a compost pile, bin, or tumbler,

Although it may be surprising, Shrimp Shells and Tails, as well as all crustacean shells are fully biodegradable. They will decompose readily in an active compost pile, and are an excellent ingredient in any compost recipe. I’ve been using shrimp shells in my compost for years, and will share all that I’ve learned.

If you are in a hurry, then I can cut to the chase right here: If you have an active compost pile, you just simply toss them in to the middle of the pile. Don’t wash them, don’t rinse them, don’t do anything but get them in the middle of the hot pile. Their C:N ratio is really low, meaning they are going to breakdown really fast (and they do, trust me).

But none the less, I thought perhaps some of you may be interested in the finer points of shrimp shells and their biodegradability. So, I will organize this article into smaller sections, as there is quite a bit of interesting information into the material make up and decomposition of shrimp and crustacean shells.

In this article:

What are shrimp shells made of

We all know shrimp, and their pesky little shells. Shrimp meat is delicious, fried, steamed, sautéed… you name it – it all tastes good. But when we think of shells, we mostly don’t consider that these were part of a living breathing organism. Well, the shell of a shrimp is made up of a few ingredients. Let’s take a deeper look into the breakdown:

Shrimp, lobster, and crustacean shells are 20–40% protein, 20–50% calcium carbonate and 15–40% chitin[1] So, whether we are talking about a shrimp, lobster, claim, or oyster- their shells are all made of chitin, calcium carbonate, and organic protein.

This went from my plate, straight to the compost bin.

Now, anything that is part of any organic lifeform can break down, and shrimp or crustacean shells are no different. We may think of clam shells or shrimp shells as being hard (which they are), but they still can and will decompose if properly composted.

Chitin – what is it made of?

Chitin is a term of a complex molecule that makes up between 15%-40% of a shrimp shell, lobster shell, or any other crustacean. Chitin is the reason Shrimp Shells are so excellent for composting. Basically, it is a combination of carbon, nitrogen, hydrogen and oxygen. The chemical formula for Chitin is C8H13O5N·H2O [2]

So, what can we learn from that chemical formula in regards to composting? Well, simply put, the C:N ratio of Chitin is 8. Meaning that Chitin is a very ‘green’ material. A perfectly balanced compost pile will have a C:N ratio of roughly 20-30 parts carbon to 1 part nitrogen.[3] That means that shrimp shells are an excellent source of nitrogen rich compost material. They will help your compost pile or bin get quite hot. And, a hot compost pile is necessary to kill any weed seeds that may be hiding in your pile.

Calcium carbonate. What is calcium carbonate made of?

The other main component of shrimp shells is Calcium carbonate, which is made of Calcium, carbon, and oxygen. The chemical formula is CaCO₃. Calcium carbonate is neither green nor brown carbon material, as it has no Nitrogen and little carbon. It is “along for the ride” in regards to composting in that it will decompose. Composted calcium carbonate adds significant amounts of calcium, but doesn’t directly feed bacteria or microbes in compost.

None the less, calcium carbonate will be greatly beneficial for adding a source of calcium to your garden though. Simply top-dress you compost onto your vegetable garden to allow the calcium to naturally infiltrate your soil.

Benefits of Chitin

In addition to being high in Nitrogen, Chitin also has antifungal properties. Research has found that compost made from chitin reduces fungus and damp-off disease of cucumbers and other plants. So, it has anti-fungal properties. [4][5]

Are shrimp shells brown or green

Shrimp shells are a ‘green’ compost material, as their C:N ratio is 8. Any material with a C:N ratio less than 30 can be considered a ‘green’ material. [3][6]

As stated above, Shrimp or other crustacean shells are made up of between15%-40% chitin. And the chemical formula for Chitin is C8H13O5N·H2O. To determine if a material is ‘brown’ or ‘green’, we just need to determine it’s C:N ratio. In this case, chitin has eight carbon atoms and one nitrogen per molecule, thus it’s C:N ratio is 8.

==>Related – 101 household items you can compost (printable list)

How long does it take for shrimp shells to decompose

The time required for shrimp shells to decompose will be determined by the temperature of the compost pile. In a hot compost pile with internal temperatures at or above 120F , the shrimp shells break down in 7-14 days. In most compost piles shrimp shells should decompose within a month. However, a cold compost pile that is not active it may take several months to decompose the shrimp shells. [4]

I can’t tell you how many times I’ve added 50-100 shrimp shells to an already active pile, only to go turn it a week later and not see ANY shells. Shrimp shells, prawn shells, crab shells, lobster shells….they all break down lightning fast in an active, hot compost pile. It is fairly incredible.

A 5 gallon bucket filled with green materials for one of my ‘Winter’ piles. You can see the shrimp shells toward the top of the bucket.

How do you prepare shrimp shells or sea shells for composting

If there is other food residue on the shrimp or lobster shells, then you should rinse the shells to remove anything like butter, oils, or sauces. This is primarily important for those with pest problems at their compost piles, or those who have small tumblers that do not get hot.

If you do not have significant pest/animal problems with your compost pile, and you have a hot & active pile, then you can just add the shrimp shells directly to the interior of your compost pile, and mix. A hot pile without pest problems will break down full shrimp shells quickly.

I personally don’t wash my shells, as I generally have a hot & active pile. The temperature of your pile really is the deciding factor if any preparation to the shrimp shells is necessary. If you have a hot compost pile, the shrimp shells will decompose rapidly, along with oils or sauces that may be present on the shell. I have done this numerous times for many years.

How to prepare other crustacean shells

For thicker crustacean shells such as mussel, clam, or oyster shells, they should be rinsed and then crushed or broken up. This is because the thick walls of clam or oyster shells will take much longer to decompose. This has to do with their surface area to volume ratio, in which is much lower than shrimp or lobster shells.

Final thoughts

Shrimp shells, lobster or crab shells, and really any other crustacean shell can be an excellent ingredient to the compost pile. As long as you build a properly balanced pile that heats up, the time to decomposition will be short. The low C:N ratio of chitin, means that these materials can add lots of nitrogen to your pile, helping everything get hotter, and thus decompose quicker.

References:

[1] – Yan, Ning, and Xi Chen. “Sustainability: Don’t waste seafood waste.” Nature 524.7564 (2015): 155-157.

[2] – Dweltz, N. E. “The structure of β-chitin.” Biochimica et Biophysica Acta 51.2 (1961): 283-294.

[3] – Cullen, Mark, Johnson, Lorraine. The Urban/Suburban Composter: The Complete Guide To Backyard, Balcony, And Apartment Composting. New York : St. Martin’s Press, 1994, pp155

[4] – Abirami, S., G. Gnanamuthu, and D. Nagarajan. “Bioconversion of shrimp shell waste into compost preparation and its plant growth study.” Indian Journal of Agricultural Research 1 (2021): 5.

[5] – Yurgel, Svetlana N., Muhammad Nadeem, and Mumtaz Cheema. “Microbial Consortium Associated with Crustacean Shells Composting.” Microorganisms 10.5 (2022): 1033.

[6] – Karen Overgaard and Tony Novembre. The Composting Cookbook: How To Make The Perfect Compost, Greenline Products, 2002. pp.76

Joe Foster

Hi - I grew up outdoors in nature - hiking, fishing, hunting. In high school I got my first job at a garden center where I learned to garden and landscape. I've been growing plants from seed and designing native plant gardens for over 10 years. I hope to share some of my knowledge with you! You may have seen some of my videos I create on our YouTube channel, GrowitBuildit (more than 10 million views!). You can find my channel here: https://youtube.com/@growitbuildit Additionally I am a wood worker / DIY enthusiast. I enjoy designing/building projects (with hand tools when I can!). I hope to give you some tips and useful information!

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