CRUSTACEAN SHELLS as Fertilizer and Soil Amendment


How might shells benefit the garden?

As shells break down, they slowly release nitrogen, phosphorus and calcium into the soil, adding organic matter and improving soil quality. Shells also contain trace minerals that benefit growth.Crustacean shells help improve soil quality

Where do I find shells?

Garden centers and online storefronts sell a variety of shell-based soil amendment products, usually packaged in large, 50 pound bags. Most are ground oyster, crab and shrimp.

Country feed stores may carry bags of crushed oyster shells used as animal feed. Check the label to ensure that there are no other ingredients in the package before using them in the garden.

If you live near the ocean, save your money and make your own shell meal in small quantities. Instead of buying a product because you lack access to the beach, save shrimp and other shells from your meals or scrounge free shells from restaurants or processing plants.

What plants may benefit from shells?

I throw crustacean shells in with my potatoes at planting time. Shells also make a great addition to planting holes and containers prepared for tomatoes.

Any plant that will eventually flower and produce edible fruits or vegetables are good candidates for shells. If I had enough, I would use them alongside all my food crops.

Crustacean shells also contain chitin, a protein-based lining of the shell (also found in the exoskeletons of insects) that stimulates microorganisms to fight off attacks from microscopic nematodes that live in the soil and damage roots.

It’s important to thwart the nematode because infestations can spread by tools, boots and soil exchange. The number of vegetables, nuts and fruits that can be damaged by nematodes in California is extensive:

Beans, beets, carrots, celery, cole crops, corn, cucumbers, eggplant, garlic, lettuce, melons, onions, peas, peppers, potatoes, radish, spinach, squash, tomatoes, grape, blackberry, raspberry, strawberry, almond, apple, apricot, avocado, cherry, citrus, olive, peach, nectarine, pear, plum and walnut.

The list above was generated from an article published by the University of California, Statewide Integrated Pest Management Program. To read the Guideline, visit the Bibliography and look for the topic, Crustacean Shells.

Combine shells with…

Shells break down slowly and the smaller the pieces, the faster the nutrients will become mineralized so they can be absorbed by plants. If you are planting vegetables that need lots of nitrogen at the beginning of their growth cycle, recommend you combine the shells with a material such as alfalfa pellets so you’ll be supplying the plants the nitrogen they need up front plus slow release minerals as growth continues.

Sometimes I throw kelp leaves and seaweed in with the shells to contribute growth hormones and enzymes to the mix. 

Crustacean Shell Soil Amendment Recipe

Save and collect shells from shrimp, crabs, clams, snails and lobsters. Crush them as small as possible. I use a few handfuls of crushed shells in the planting holes of my potatoes and tomatoes. If I’m feeling lazy, I don’t crush freshly collected shells – I place them under the soil beneath the transplant or seed and scatter around the root zone.Use crustacean shells in a garden

Crustacean Shell Liquid Fertilizer Recipe

To create a liquid fertilizer from shells, crush or grind the shells up into small pieces – the smaller the better to get the most surface area in contact with the water. Add a few handfuls of crushed shells (about a cup) to a gallon of water and let it sit, loosely covered for two days.

Some of the minerals in the shells will dissolve in the water, creating a natural emulsion to feed your plants and soil microbes. Pour the liquid around your plants, fill the container again with water if you need more, or add the shell solids to the compost or planting hole.

Crustacean Shells Quick Tips

  • Add shells to your compost pile. The best position to start is in the middle of the pile where they will be subjected to the most heat.
  • Wear protective gloves when you crush thin shells so you don’t cut your fingers. Protective eyewear may be in order too, depending on how wild you’re feeling.
  • Children have lots of fun crushing shells. Please take the safety precautions mentioned above and adjust based on the child’s age and temperament. A brick works great as the “crusher”. Place a small amount of shells on top of a flat stepping stone. Make sure to hold the brick well away from the crushing end. Gently smash the shells. This works much better than a small rock because little ones tend to get their fingers caught underneath the stone. Once a small batch of shells is crushed, it can be easily brushed (with gloved hands or tool) into a container.