sea shells in garden soil

Sea shells In Garden soil: improving your soil

If you have ever grown tomatoes only to discover they are suddenly afflicted with blossom end rot just as the fruit ripens, you already know how important calcium in the soil is to plant growth. What you might not know is that putting sea shells in garden soil will provide your plants with a ready source of calcium while improving the soil, too. Find out how sea shells in garden soil can help you grow a more bountiful garden this year.

Are sea shells good for garden soil?

Yes, ground or crushed sea shells are good for your garden soil. They provide nutrients and improve the texture of the soil. They are also all-natural, so you don’t need to worry about contaminating groundwater or harming birds and insects. Sea shells are an excellent choice as a soil amendment.

How do they improve the soil?

Sea shells improve garden soil in two ways: by improving the structure and pH of the soil and by providing nutrients to your plants.

The shells help to aerate and improve drainage of your garden soil and prevent it from compacting after rains. They also provide nutrients and help to balance the pH of your soil. Generally, seashells raise the pH of the soil and can replace liming the soil. Be aware that while sea shells are a great option for your soil if it is acidic (pH below 7.0), it may raise the pH too high in alkaline soil (pH above 7.0).

asparagus shoot coming through the soil
High pH crops like asparagus benefit greatly when soil is amended with seashells

The shells of shellfish contain a slow-release source of nitrogen, called chitin, that boosts plant growth. According to a Washington Post article, when you add sea shells to your soil, it encourages the growth of chitin-eating bacteria to break down the shells. Once shell decomposition is complete, these same bacteria seek out other sources of food and attack harmful garden pests, like nematodes, in the soil. This further improves the health of your soil.

Sea shells also contain high amounts of calcium an important nutrient for plant growth. According to CropLife, calcium is needed to build cell walls and cell membranes in your plants. Without adequate amounts of calcium, plants may drop their blooms or fruit and suffer from slowed growth. Blossom end rot in tomatoes is commonly attributed to a calcium deficiency. 

What type of shells should I use?

Oyster shells are the most popular sea shell used for amending garden soil, but other shells can be used, too. Lobster, crab, mussel and clam shells can also be used to amend your garden soil. These shells can all be purchased as either crushed or ground shells. While crushed shells are attractive and can be used for mulch and other landscaping needs, ground shells will work the fastest for improving your gardening soil.

oyster shells in a persons hands
Oyster shells make a great amendment for your soil

How many shells should I add?

The amount of ground or crushed shells your soil requires depends on the condition of your soil and the product you are using. In general, you should apply 4 to 6 pounds of ground shells per 100 square feet of garden area. Check the application rate on the container and follow the recommendations of the manufacturer when using commercially produced ground shells. If your soil is acidic you may need to add more shells to the soil.

Where do I get sea shells?

You can purchase ground or crushed sea shells from home improvement centers, gardening centers, and many outlets online. Look in the organic gardening section and read the label carefully to determine whether the contents are ground or crushed. Ground sea shells will be powdery, resembling lime, while crushed sea shells will contain larger pieces of shells.

seashells on a beach shore
Seashells can be found on most beaches or in garden centers

You can also make your own crushed or ground sea shells. Save the shells whenever you cook seafood or check with local seafood restaurants to arrange to take their old shells.  Many will gladly give them to you as they are often headed to the landfill anyway.

How do I make my own ground or crushed sea shells?

Making your own ground or crushed sea shells takes some work, but it can be well-worth the effort. Here’s what you need to do.

1.    Boil the shells in water to clean them and remove any traces of salts.
2.    Rinse the shells with clean water.
3.    Allow them to dry in the sun. Dry shells are easier to work with and can be stored in an airtight container without worries of moisture buildup in the container.
4.    Place the shells inside a plastic (or burlap) bag and use a hammer to break them down. This may take some work, but the more effort you put in now, the sooner you will see the results of your hard work.

How often should I add them?

While you can add ground shells at any time, it is best done in the spring when you till your garden soil.  Spread the ground shells over the top of the soil and work it into the top 6 inches with garden tiller or hand tools. Water the soil well to settle the soil and prevent any loose ground shells from blowing away in the wind. Alternately, you can amend the soil with ground shells in the fall when you clean up your garden beds.

Sea shells in garden soil

Shells used as a soil amendment should be added wherever you grow plants. While many prefer to amend the entire garden bed, you can add the shells in individual rows are planting time, if you prefer. Be sure to work them into the existing soil before planting seedlings or sowing seeds. Using a cultivator or a tiller can help minimize excessive labour.

worm moving through loose soil with seashells in it
Adding seshells to garden soil aerates the soil and helps to prevent compaction

Can I use crushed shells as mulch?

Yes. Crushed shells can be used as mulch in the garden. Layer 2 inches of crushed shells on top of the soil around the base of your plants. Mulch from crushed shells helps to retain moisture in the soil and provides an effective weed barrier. It will also release calcium and other nutrients into the soil when it rains. 

Adding ground or crushed seashells to garden soil is a natural way to improve your garden soil and to boost plant growth. They improve the texture of the soil, improve drainage and provide your plants with vital nutrients they need to thrive.


Seashells are an excellent amendment for your soil. They are inexpensive to buy and provide a long list of improvements. Start your soil improvements today!