Crab shells in garden

‘Hello Garden Doctor,
I have heard that dried seaweed collected from the beach can be used as a beneficial addition to the garden. Just wondering if there are any other materials found at the beach or anywhere else that can be used as an organic garden addition?
Very thankful for any of your thoughts on this, Greg’

Natural organic fertiliser is the best way to feed your plants and improve your soil. The sea contains a large spectrum of trace elements in solution, and some of the debris that is washed up on the beach like seaweed, shells and rocks also contain quite a lot of these trace elements. After foraging at the beach on many an occasion I can tell you of quite a few materials that can easily be collected at the beach and recycled into the garden as organic fertiliser. The many types of shell, seaweed, sea sponge, cuttlefish and even pumice stones can all be used in varying ways that will benefit your garden.

Mulching with any of these materials will be beneficial. It will improve the soil, retain water and reduce the weeds. Seaweed is perhaps the best known of natural fertilisers from the sea, though shells have also been used in the garden for thousands of years. You can easily use crushed up seashells as a layer of mulch just like pebbles are used in some gardens. Be sure to thoroughly wash and then soak the shells in a bucket of water as seashells will be encrusted with salt. Pour off the water after two days and then soak the shells again to make sure excess salt has been leached out otherwise this could harm your garden. There is no need to break up small shells, so just collect those ones. You should really be able to find enough small shells pre-crushed by nature.

Collect all the crushed shells and apply a layer over the garden surface. To do this, simply throw or sprinkle the crushed shells out over the site you want to mulch, These shells will provide the soil the minerals and calcium as they decay, providing a good natural slow release fertiliser that is also organic. The great benefit is that the shells decay very slowly, preventing the need to replenish the mulch for at least a few years, and it is good for all types of plants such as flowers, trees, ground covers and many other herbs and vegetables. If at any time you need to compost around your plants, simply rake the seashells aside add compost, and then replace the shells back on top. You can use seashells as a surface mulch of your potted plants such as flowers or succulents, enhancing their appearance. You can also mix the sea shells into the soil and the coarseness will improve the drainage, which would be beneficial for any plant that likes a well-drained soil.

Using cuttlefish or even crushed lobster and crab shells can also be beneficial to the garden. Cuttlefish like all other shells is composed of calcium which is an important element in plant nutrition. After nitrogen, potassium and phosphorus, calcium, magnesium and to lesser extent iron are essential for plant growth. Cuttlefish bone is a pure form of calcium carbonate. Pulverised cuttlefish should be sprinkled around the garden, your pot plants and definitely in the compost. It is soft and easily broken into small pieces if wrapped in a cloth and hit with a hammer or large stone. It is a very useful way to provide a natural organic slow release of organic calcium. Crushed cuttlefish bone is an alkaline substance and is also very useful for neutralising soil acidity.

Pumice stones that can also be found washed up at the beach are also another useful addition to the garden. Pumice stones are very light, airy rocks that float on water. They originate from volcanic regions and contain many beneficial minerals for the garden. They can be broken up into chunks and added to the compost or around the garden as a slow release fertiliser. Pumice is soft and easily crushed. If the rocks are pulverized into dust then the mineral release will be much quicker. Pumice is beneficial for both clay and sand soils, helping to provide aeration in clay soils, and water retention for sandy soils.

Seaweed is the number one gift for your garden, as it contains an abundance of beneficial minerals and trace elements. It’s just too hard to walk by it at the beach and not pick it up. I prefer to take the dried seaweed, because that way you can fit more into your bag, and will be more concentrated in minerals by weight.

Crush it up in your hands or add it whole to your compost and garden beds, it is really one of the best things you can do for your garden. Seaweed is packed with everything that a plant and soil needs. The trace elements contained in the seaweed are transferred to the soil and then into the plant and its fruit. Seaweed is a good way of adding iodine to the soil. Iodine is a very important nutrient for human health, and these days many of the soils used for agriculture and the people eating the produce from them, are deficient. To make seaweed ‘tea’ fertiliser, soak seaweed in a container for a week or two until it begins to resemble the colour of tea. By this time it will contain all the trace elements and nutrients released from the seaweed. This would be far too strong to use on its own, so make sure to dilute a small cup with a full watering can and water it around the garden.

Seaweed itself contains little salt it is the sand attached to it that is quite alkaline and needs to be removed with a good wash. Seaweed can be used around almost any plant except acid loving plants such as strawberries. Sea sponge also contains many of the trace elements and minerals found in seaweed. When added to pot plants or sandy soils sea sponge will retain water (it is a sponge after all!), particularly useful for drought prone areas. Sea sponge is like a natural water crystal, absorbing and retaining moisture in the soil. Some people even use sea sponge as a medium in which to grow herbs without soil!

Put the seaweed, sea sponge, shells, cuttlefish and pumice in the compost as well as in the garden beds. With all of these items collected from the seashore be sure to thoroughly wash or soak them to remove excess salt which may leach out over a few days. All of these materials are a valuable, efficient natural source of fertiliser and mulch. The best bit is you can enjoy a walk along the beach whilst collecting it and it’s also free! With these additions your soil will be better off allowing you to save money and avoid using chemical fertilisers as soil additives or amendments.

Dr. Kris
Garden Doctor
Contact: [email protected]
Copyright © 2013 Dr. Kris
You can read all past articles of Garden Doctor at

Oyster Shell

There might be many more uses for your kitchen scraps than you realize.

Specifically, the empty oyster shells from your last seafood feast have some surprising benefits for your lawn and garden. It might seem like too much time and effort to turn these shells into a form that your plants can pull nutrients from, but the truth is that the process is easier than you expect. With just a little pre-planning and effort, you can add the nutrients of one of nature’s best forms of natural calcium and minerals right where the roots of your plants can take advantage of them.

We realize many of you are landing on this page in hopes to purchase oyster shells and we apologize, but we do not sell them. However, you can purchase them from our affiliate here.

What Are Oyster Shells?

As the name implies, oyster shells are the hard exoskeleton of a variety of mollusks that are in the family Ostreoidea. Most oysters live in saltwater or brackish environments. Additionally, their shells tend to contain high levels of calcium carbonate (about 96%). When oysters die in the ocean, their shells create reefs that are habitat space for dozens of other creatures. For this reason, they are considered a keystone species.

Oyster shells have plenty of benefits on land as well. When ground into a fine powder, they are a high-quality soil additive due to their calcium and micronutrient content. Adding crushed shells to the soil produces a long-lasting release of nutrients. This results in regulating pH levels and increasing the intake levels of fertilizer for your garden plants. Crushed shells also help to create habitat spaces for soil microbes in compost piles, which helps them to break down compost piles faster.

Where Can You Get Oyster Shell?

Crushed oyster shells can be bought from most landscaping supply companies. However, the quantities they are sold in means that getting enough shell for your lawn or garden might get expensive. Although, a better idea is to collect them yourself if you live near the ocean or simply contact a local seafood restaurant to see if they are willing to set you up with some of their daily shell garbage.

When you collect your own shells, be sure to wash and boil them before adding them to your soil. This is important since the sea salt that naturally gets encrusted on these shells can burn your plants if it builds up too much. After washing them thoroughly, you can break the shells into smaller pieces by covering them with a cloth and using a hammer to pound them into a powder.

Instead of using whole oyster shells and having to crush them yourself, you may also find using oyster shell flour provides the same benefits.

How Does Oyster Shell Benefit the Soil and Crops?

There are plenty of ways that oyster shells are useful for your garden. Their calcium content helps to balance soil pH levels, improves nitrate uptake, aids enzyme formation and strengthens plant cell walls. If you’re growing leafy greens like lettuce and spinach or cruciferous vegetables like cabbage and broccoli, adding powdered oyster shell to your soil will make a big difference in your plants’ overall growth rates and vitality. The coarse texture of oyster shells also helps to reduce compaction in the soil. And, it helps prevent potted plants from getting waterlogged by allowing water to run through the soil without getting trapped along the way.

As it turns out, oyster shell has plenty of advantages for your home besides the fertility of your garden. Because oyster shells are almost pure calcium carbonate, they make a useful supplement for poultry farmers that want their chickens to lay thick-shelled eggs. You can also use oyster shells to keep garden pests away. When applied at the openings of their tunnels, the sharp shards and gritty texture also works as a deterrent in the soil to keep moles and voles far away from your plants.

General Application Rates

There are many different strategies for applying oyster shells to your garden. The best time of year to add oyster shell mulch is in the late spring or early summer when the soil has warmed up. Apply the crushed shells over your garden in thick layers, depending on how much you need. When used for garden plants, about four to six pounds per 100 square feet is ideal. Although when used as a mulch, layers about two inches thick are best.

After adding oyster shell to your soil, be sure to water it in thoroughly. This will allow the pieces to chemically interlock and become rooted in the soil so that they don’t blow away.

Making Oyster Shell Tea

Another smart strategy for using oyster shells is to brew them into a vinegar tea. Once you have crushed your shells, soak them in an apple cider vinegar mixture (one part shells to three parts vinegar) in order to pull out the calcium carbonate. After brewing for two to three weeks, you can mix a quarter cup of the mixture into a gallon of water and apply directly to your soil.

Composting Oyster Shells

Another method of getting garden benefits out of oyster shells is to use them in your compost. Not only will they balance the acidity levels in your soil, they will also create high-quality habitat space for beneficial microbes. This will allow the microbes to eat through your pile and turn it into available and delicious soil nutrients.

Before adding oyster shells to your garden be sure to clean them thoroughly by boiling and then break them into small pieces that resemble crushed gravel. Add a layer of carbon materials like dry leaves and twigs and then add nitrogen material like grass clippings or food scraps. Next, add a layer of oyster shells to the top and cover them with a 2-inch layer of manure. You can create as many compost layers as you like. Additionally, water the mixture at least twice a week in order to keep it damp but not saturated. Sift the pile every few days to increase air circulation. Finally, add the entire mixture to your garden when individual pieces of shell or vegetable scraps can no longer be identified.

Additional Tips For Using Using Oyster Shells

Keep these suggestions in mind when using oyster shells in order to get the best results for your garden.

  • Shards of an oyster shell can be incredibly sharp. This is why you should be sure to keep them far away from places where bare feet will be traveling!
  • Different forms of crabs, oysters, and other sea creatures can have different levels of calcium in their shells. Therefore, don’t be afraid to work with a variety in order to learn what works best for your soil.

Mulching with Seashells to Add Calcium

Mulch with Seashells to Add Calcium

Choose a semi-permanent material that is slow to decompose

Mulching your garden is generally thought of as the single-most important thing you can do to help maintain your garden beds. Regular mulching helps hold moisture in the soil, keeps root temperature eve, and also controls weeds by either blocking or smothering out the weed seeds. By using natural mulch, you are also contributing to a stronger soil structure in the landscape. As the mulch breaks down, it is integrated into the soil, thereby creating a system that helps better support your plants. There are many types of natural mulch with strong organic matter percentages: Leaf mold, cocoa shell mulch, shredded bark, pine needles, straw, wood chips, and grass clippings, for instance. Even compost can be used as an effective mulch if a heavy layer is applied as a topdressing over the soil. Do not use horticultural fabric under mulch; weeds continue to form on top of the fabric and it does not allow nutrients to enter the root zone. Simply place the mulch directly on to the soil.

There are times, however, when it is appropriate to choose a mulch that does not break down as quickly. Decorative mulches with a long shelf life include lava rock, shale, river stone, small pebbles, lime and granite screenings, glass, and seashells. Utilizing seashells as mulch is an excellent garden hack (especially in areas where shells are used for road beds and are practically free) for adding calcium and phosphates to the soil as well as for deterring snails and other insects that do not like the sharp shell edges.

Much like pebbles, seashells help hold the soil in around a planting bed and keep the soil cool and moist. Although many companies are now dyeing seashells, it is better to choose an all-natural, undyed lot. Maintenance for this type of mulch is simple: Regularly blow debris off with a leaf blower. Seashells are not a solution for wet or consistently damp areas as the seashells will become overgrown with moss. Sunny sites are best. Eventually the seashells will start to decompose, but it takes years and years for this to happen, making them a decorative and creative mulch solution with longevity.


Cover courtesy of Cool Springs Press

More from 101 Organic Gardening Hacks:

  • Self-Watering Containers
  • Homemade Seed-Starter Soil

For more gardening hacks and ideas, come to the MOTHER EARTH NEWS Fair where Shawna Coronado will be taking questions and presenting on organic gardening hacks and gardening with chronic pain.

Reprinted with permission from 101 Organic Gardening Hacks by Shawna Coronado and published by Cool Springs Press, 2017.

Gardening Techniques
In 101 Organic Gardening Hacks you’ll find the top tips, tricks, and solutions Coronado has dreamed up in her career as one of America’s most creative gardeners. Some are practical time-savers; others offer clever ways to “upcycle” everyday items in your garden. One characteristic every hack shares is that they are completely organic and unfailingly environmentally friendly. Order from the MOTHER EARTH NEWS Store or by calling 800-234-3368.

Organic Fertilizer For Composting Process- Crab Meal

Organic fertilizer can be found in many different forms. It can be created from plants, leaves, food wastes and from fish. Organic fertilizer from fish can then also take different forms. One of those is from the shells of crustaceans such as crabs and lobsters. These shells are very rich in nutrients that create a great growing environment for flowers and vegetables. Crab meal is found at most fertilizer centers, and can even be made on your own.

What Is Crab Meal?

Crab meal organic fertilizer is the kiln dried shell of the crab that has been ground down to dust. Crab meal has a protein in it called chitin. This protein make up is what makes the crab meal such a wonderful organic fertilizer. By itself, crab meal provides a slow release of nitrogen to the soil. This nitrogen will give the plants a very strong stalk and deep green appearance.

Other fertilizers can also benefit from the use of crab meal. Because of its great slow release qualities, crab meal will also defend the plant against ringworm. The chitin protein protects the plants giving your vegetables and flowers a healthy growing process without the use of pesticides and harmful chemicals.

Using Crab Meal Organic Fertilizer

Fertilizing your garden with the use of crab meal can be done on its own or combined with the use of other fertilizers. When combined, the manufacturer usually has their own directions for use. The same it true of crab meal fertilizer by itself. These instructions are unique to the composition of the fertilizer and for the desired application.

Because you can actually make crab meal yourself, there are also instructions that are generally agreed upon. For specific vegetable and applications the use for the crab meal will be different. For instance, vegetables should have 5 lbs for each 50 foot row. Other uses include:

  • House plants at 2 ounces per flower.
  • Tomatoes at 4 ounces per plant.
  • Trees at 4 lbs. per tree.

When sowing the plant you should till the fertilizer into the soil before planting. If the plant is already in the soil, then tilling around the plant or simply spreading it around the base will be sufficient for a successful growing season. This is not a water soluble fertilizer. It must be applied by itself.

Mulching your garden bed has some great benefits. Mulch will hold moisture and keep weeds from starting around the plant. However, it is also useful for helping the crab meal better keep the plant fertilized. Spread the crab meal into the mulch and the time release qualities of it will continually feed the plant. You can also add some crab meal to your compost bin for an added boost in nutrition.

Crab meal makes for a tremendously beneficial organic fertilizer. Its time release quality will not over fertilize your plant, but will give it the nitrogen and protein it needs for beautiful, vibrant, and healthy produce. Use it on your trees, vegetables, or flowers for great results.

What Is Shellfish Fertilizer – Using Shellfish For Fertilizer Needs In The Garden

Gardener’s know that amending the soil with good organic compost is the key to healthy plants that produce prodigious yields. Those who live near the ocean have long known about the benefits of using shellfish for fertilizer. Fertilizing with shellfish is not only a sustainable method for utilizing the otherwise useless parts (shells) of crustaceans, but also imparts nutrients into the soil. What exactly is shellfish fertilizer? Read on to find out about fertilizer made of shellfish.

What is Shellfish Fertilizer?

Fertilizer made of shellfish is composed of the shells of crustaceans such as crabs, shrimp or even lobsters and is also called shrimp or crab meal. The shells, which are rich in nitrogen, are mixed with coarse carbon rich material such as wood shavings or chips, leaves, branches and bark.

This is allowed to compost over the course of several months while microorganisms feast on the proteins and sugars, effectively converting the pile into rich humus. As the microorganisms feed on the shellfish

proteins, they generate plenty of heat, which reduces pathogens, thus eliminating any nasty, fishy odor and at the same time killing any weed seeds.

Crab meal is readily available online and at many nurseries or, if you have access to significant amounts of shellfish material, you can compost the shells yourself.

Using Shellfish for Fertilizer

Shellfish fertilizer contains about 12% nitrogen along with many trace minerals. Fertilizing with shellfish allows for a slow release of not only nitrogen but also of calcium, phosphorus, and magnesium. It is also rich in chitin that encourages healthy populations of organisms that deter pest nematodes. Plus, earthworms love it.

Apply shellfish fertilizer several weeks prior to planting the garden. Broadcast 10 lbs. (4.5 kg.) per 100 square feet (9 sq. m.) and then rake it into the top 4-6 inches (10-15 cm.) of soil. It can also be worked into individual planting holes as you transplant or sow seeds.

Crab meal can help deter not only slugs and snails, but ants and grubs as well. This organic fertilizer doesn’t burn plants like some other fertilizers because it is slow release. It is safe to use near water systems since the nitrogen doesn’t leach out of the soil and into water runoff.

When shellfish fertilizer is tilled or dug in well, it helps plants fight off root rot, blight and powdery mildew while encouraging healthy populations of microorganisms and earthworms. Also, because the muscle proteins in shellfish (tropomyosin), which cause allergies, are eaten by microorganisms as they compost down, there is no danger to people with shellfish allergies.

Really, all in all, it is an excellent organic fertilizer option, one that in the past would have been just been dumped back into the sea with the potential to overload the ecosystem.

Crab Meal

  • Crab meal contains a set of vital nutrients comparable to those in the best fertilizers, including a whole array of trace minerals.
  • It naturally releases nutrients slowly, which is better for plants and growing media.
  • Only a little bit of crab meal needs to be used to obtain its benefits in limited space.
  • The high protein content provides foundational building blocks for terpenes and cannabinoids.

Benefits for Outdoor Gardens

  • Crab meal is 100% ecologically friendly and will not damage the outdoor environment.
  • The natural reactions caused by its chitin have a protective effect against nematodes.
  • It defends against fungus development like botrytis and also prevents blossom end rot in tomatoes.

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Shrimp Shell Meal

Question from George:
I’m having problems finding the shrimp shell meal you talked about at the fairgrounds the other day, the only place I can find it is on line and its a 50lb bag. If I bought the 50lb bag how long can I store it and it still be good. It would take me maybe 2 or 3 years to use that much with my small garden. How much would I use per square ft.?

Answer from Pat:
Shrimp shell meal appears to be an effective control for nematodes. As I stated in my talk at the San Diego Fairgrounds it contains chitin (the material out of which the exoskeletons of insects and crustaceans are made.) It also contains chitinase (an enzyme that eats up and destroys chitin.) The effect is slow starting since when combined with soil the chitinase first spends approximately four months consuming the chitin in the shrimp shell product and then having nothing else to eat and having multiplied, the chitinase consumes the nematodes and the effect can be reasonably long-lasting but one might need to add small quantities to the garden soil. (Not having used the product myself I am not sure of the intervals at which it needs to be added.)

The answer to your question about amounts to use can be found on the website of Peaceful Valley Farm and Garden Supply but you will need to do some math to figure out how to use a small amount. I would just try with a pound or two for ten square feet being aware that it works best in moist soil and also is somewhat alkaline. Here is the link for shrimp shell meal. It’s worth every penny since it really appears to be working and some people mix some into their compost.

Up to now I have not found a source of smaller quantities of shrimp shell meal. As I also stated in my talk, the only regular source I know of is Peaceful Valley Farm and Garden Supply which sells the product for agricultural purposes in fifty pound bags. It is unfortunate that some of the effective organic products are sold in containers too large for home gardeners. Until this problem is cured, each home gardener who has this problem needs to find his or her own solution. Some company could make a good business of bagging this product in smaller quantities and selling it to organic gardeners. You might try Cedros Gardens and see if they carry it in smaller containers. Anderson’s Nursery in San Diego is another possibility.

I cannot solve the amount problem, but suggest you bag some and share with friends or a garden club. My ideas for you are these: Contact an organic gardening club and see if they wish to share the unused remainder of what you will have. Bag it in smaller plastic and brown paper bags and sell it yourself on e-Bay. You might find it sells well if you write the ad in a good way to attract sales. You could even try selling it to a local nursery that sells organic products. Or sell it yourself at meetings of the San Diego Horticultural Society. It might sell quite well if you write a good label.

One of my daughters used this product in her own home garden. I am unsure of the exact amount she used since she said when I asked that she used “a few pounds”. She added it to her raised beds in which she had a bad nematode problem. It worked for her and all her vegetables are now flourishing. There are no package directions but she read the information on the website and figured all she needed was only a few cups for the size of the area she needed to cover. I am sorry I am unable to give more specifics on how much to add. Phone or email Peaceful Valley to find out how long you can store it. My daughter has had her bag of this product for 6 months so far and it still works.

Shrimp Meal

Soil Amendments and Fertilizers

Thriving sustainable agriculture is built on the ground of a healthy soil. In fact, organic certification requires a soil management plan. Do a soil test to determine your soil’s needs before embarking on a program of soil improvement. Check with your local Cooperative Extension for testing in your area, or consider our testing and recommendation service.

Soil amendments used with a program of crop rotation, composting and cover cropping can enhance fertility, improve soil tilth, promote disease resistance, support beneficial soil microorganisms, and even help restore balance to the garden and the world around it. Application rates vary depending on soil type and results of soil tests.

Fertilizers provide nitrogen and other nutrients in a form that is readily available to plants. Organic fertilizers can provide both an immediate boost and additional long-term fertility, feeding both the plants and the organisms that maintain soil health. We also offer soil amendments that have limited available plant nutrients but help to remineralize the soil, improve soil structure, or provide a long-term slow-release source of plant nutrients. Foliar sprays get nutrients directly to the leaves and can increase resistance to disease and to insect infestation.

Analyses provided here are those provided by the manufacturers, or, if none are available, from a Maine state lab test performed on our most recent lot: there is some variability in the nutritional analysis of natural fertilizers, so view these numbers as guides, not gospel. Fertilizers should be used as a supplement to, not a replacement for, the nutrients provided by healthy soil. Sustainability requires developing a long-term plan of cover-cropping, green manuring and composting.

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