How to use crushed shells as mulch

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How to use crushed shells as mulch
Seashells have long been used as decoration for the home and garden. (Juan Silva/Stockbyte/Getty Images)

People have used seashells for thousands of years for their decorative properties. Whether purchased in bulk from feed stores or garden warehouses, or simply found laying around in nature, seashells add an instant nautical-themed natural touch to any environment or decorative theme. However, for gardeners, shells have important properties that extend far beyond the ornamental. When crushed and used as mulch, shells can have many benefits for the garden, both cosmetic and practical.

Skill level:

Things you need

  • 0.907kg. seashells per square foot of garden space
  • Hammer
  • Potato sack or thick cloth
  • Large pot
  • Water
  • Stove
  • Watering hose

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  1. 1

    Purchase the shells. Obtain enough shells to cover your garden with a layer of mulch at least 1 inch thick. This usually amounts to 0.454 to 0.907kg. of shells per square foot of garden space. Purchase the shells from a feed supply store, which sometimes sells them pre-crushed or even ground into coarse chunks. You can also collect them yourself at the beach, though this may be time-consuming, particularly because you will need to remove all traces of sea salt from shells before placing them in your garden. Another alternative is to contact a local seafood restaurant and offer to take their excess shells. These will require boiling to clean off excess fish matter.

  2. 2

    Clean and prepare the shells. If they have not been thoroughly cleaned, boil and rinse the shells before placing them in the garden. Bits of organic matter still clinging to the shells won't hurt your garden, but may cause a serious stench over time and attract rodents. Sea salt can affect the chemical composition of the soil and hinder your plant growth, if not kill some species of plants and vegetables that prefer a more alkaline soil composition.

  3. 3

    Crush the shells. If the shells are not already crushed, place them in a cloth sack, tie off the end to close it, and strike the shells with a hammer a few times until they are crushed to your satisfaction. Ensure that the end of the sack is closed tightly in order to prevent injury from flying bits of shell debris. Break them into small pieces no larger than 1cm in diameter; larger pieces may sink into the soil over time and act like rocks to prevent root growth.

    How to use crushed shells as mulch
    A few strikes from an ordinary hammer will crush most sea shells. (the hammer image by Jim Mills from
  4. 4

    Layer the mulch on top of your garden. Sprinkle the crushed shells evenly over your soil. Sprinkle the shells in layers at least 1 inch thick, if not 2 inches, but no thicker. Shells are heavier than traditional cedar mulch and can weigh down the soil, making it difficult for plants to stretch out their root systems.

  5. 5

    Water your garden. The water helps the shells to interlock and settle into a tighter formation over the soil, preventing wind erosion and making your new shell mulch cover that much more permanent.

Tips and warnings

  • Fertilise your garden before mulching with crushed shells. Moving shells aside in order to fertilise, then moving them back into position, can be an extremely labour-intensive endeavour.
  • Crushed seashells are the perfect mulch and ground covering for seaside gardens.
  • If your soil is already very rocky, consider using another type of mulch. Shells will eventually make their way into your soil, giving it a much more rocky consistency over time.
  • Shells leech calcium into the soil. While this is beneficial for many kinds of plants and vegetables, it can be a repellent for others. Make sure your garden can handle larger quantities of soil calcium.

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