Food Plants - AnnualFood Plants - PerennialSoil RehabilitationWaste Systems & Recycling

Adding Calcium One Egg at a Time

by Rick Pickett, Eco-Ola

Building soil fertility in the humid tropics is a difficult project. Not only because the soil itself is thin, but due to the fact that below the fertile surface of leaf litter, rotting trees and decaying organic matter is a mineral and nutrient deficient zone of usually acidic clays called oxisols or, less commonly, utisols. With up to 90% of tropical forest biomass living within the plants and organic matter and only a paltry 10% occurring in the actual soil, protection and cultivation of soil is extremely important in sustaining fertility.

For many of our farm partners, like Federico, we’re rehabilitating slashed-and-burned lands that have been heavily leached of nutrients or are lacking the balance of minerals needed to allow plants access to important nutrients like phosphorous. One technique used extensively in tropical climates to take advantage of oxisols is the heavy application of lime or calcium carbonate to raise the soil pH and begin improving the soil structure and mineral availability for plants.

We would love to pump multiple metric tons of lime or calcium into the soil, but our distant location from traditional sources and concerns about mineral extraction practices makes large-scale delivery undesirable. But, our plants need their calcium. What to do?

… Enter the mighty eggshell.

Composed of 98% calcium carbonate, eggshells are an untapped source of calcium, but in their solid form they are very slow to decompose into a form ready for plant uptake. To change the eggshell into a soluble form, we need to use vinegar (acetic acid) to breakdown the calcium carbonate and transform it to water-soluble calcium acetate. From there we can use the diluted solution as a foliar spray on the plants for fast absorption, usually in 24-56 hours.

Calcium is an essential nutrient for cell wall reinforcement as well as protein synthesis, water transfer and carbohydrate translocation. The challenge is that calcium is mostly immobile in plants and won’t be sent to areas in need. By applying a bi-weekly treatment of calcium acetate mixed with other nutrients, we’re able to counteract the calcium-deficient soils and provide needed nourishment for the plants.

The Solution

Two-months ago we started collecting eggshells from various restaurants in Iquitos, especially Dawn of the Amazon Cafe, and food vendors in the Eco Ola Permaculture Capital of the Amazon, Mazán. Instead of letting more organic waste be trashed in the local dumps, we’re able to recycle these essential minerals for improving plant health and robustness.

The process goes like this:

  1. Eggshells are picked up daily in Mazán or delivered weekly to the farm from Iquitos
  2. The shells are sun-dried to evaporate any moisture, limit pests and reduce toasting time
  3. Shells are then crushed to increase surface area to further reduce toasting time
  4. We toast the shells over a wood fire until the majority have a nice black char to them (we’ve noticed over multiple solutions that the shells seem to dissolve faster with longer toastings
  5. A volume mix of 1:1 of table vinegar and toasted eggshells is prepped and shaken in a bottle
  6. Every day we shake the bottle and add more vinegar as space is created in the production of carbon dioxide gas
  7. In roughly four-weeks the eggshells have mostly dissolved and we use a 15-21 tablespoon dilution in 15-liters of water for foliar spraying

Toasting the eggshells is a bit unpleasant, especially at first when we were toasting them wet and filled with maggots. At least the maggots added some additional nutrients, but introducing the sun-drying before toasting has made the process much more pleasant. But, do be warned, as you will reek of toasted eggshells, especially if doing multiple batches.

We look forward to documenting the process and sharing photos of our test plots of the solution with you all!


  1. Nice work Noah and team.

    I’m just thinking out loud, and wondering if it’s better to, instead of converting the egg shells into a water-soluble form and applying as a foliar spray, if stopping your process half-way through, and applying it to the soil instead, where micro-organisms can do the rest of the work, ensuring plants get the appropriate amounts, might be a healthier and more natural way to go? I’m no expert on tropical soils, so your thoughts, and the thoughts of others reading would be interesting to hear. My studies in soil science lead me to prefer feeding the soil, and letting microorganisms do their thing, instead of trying to bypass them to feed plants directly – as plants can ultimately take more than they should, leading to imbalances.

  2. Excellent work.
    I’ve often used excess egg shells in my compost pile. Much as the first commenter said, letting the soil organisms do the work. Less energy used. Less heating, and less effort. Egg shells can be dried in the sun as stated, then crushed, and then scattered/mixed into the compost. Then the calcium will be freed by the compost organisms, and when distributed with the compost, directly feed the plants.
    Noah’s foliar spray is both instant, and much more work than a permaculture system needs to have, and if I had to dry, crush, toast and then dissolve egg shells continually, I would give up.
    I’d probably just drop egg shells onto my mulch, and let the rain and soil organisms do the work.
    A continual supply of egg shells administered in this manner will eventually correct the soil Ph. Also the underlying soils will benefit in the long term.

    1. Rick makes the point right at the beginning of his article that the soil in question would require many tonnes of lime added to the soil to change the pH to a level where the plants would be able to access enough calcium from it.
      Foliar feeding with Calcium acetate made from egg shells is a smart way around the problem I reckon.

  3. Well it sounds like they do need to get the calcium very quickly into the plants and so I guess they do what they need to do to get that done.

    I do save our household eggshells for a couple of weeks by simply letting them air dry on top of the outside fire drum lid. Then when I light the fire they too get roasted on the lid at very high temps. I then simply crush them up by hand as I scatter them into the chicken pen thick mulch. They crumble up very easily almost effortlessly in this state, without injury too as opposed to doing it when they’re uncooked…

  4. I follow this simple and low-tech approach: I gather the washed eggshells in a big bowl that is kept outside, in a sunny location. As the time goes by, the bowl fills up, so I take the shells, (which by that time have become very brittle and hopefully “dissinfected” by the sun) and simply put them in an old food processor. The result is a nice, whitish powder (which by the way smells so nice that almost makes you want to eat it), that goes directly to the soil, around the plants in the veggetable garden.

  5. I think the direct to plant application is the more appropriate option here. There is one fact of tropical soils, stated in the article, which is 90% of nutrients (and the biomass that will actually hold onto the nutrients and create cation exchange sites) are tied up in living plant tissue. Since the tropics soil issue is nutrient leaching due to high rainfall it would reason to me that applying nutrients directly to the plants themselves would be more efficient for the capture and storage of those nutrients than feeding the soil. The nutrient storage pattern of the tropics is vegetation. Work with nature. Great article!

  6. Ingenuous, however that’s a lot of effort to dry/cook/crush/dissolve what not.

    Isn’t it just easier to feed broken egg/seashells to chickens*? They reuse the residual proteins, and while they take a small cut of the calcium, a lot of calcium is excreted again pre-crushed with rock minerals (chickens swallow stones for gizzard/digestion). Chicken manure is invariably alkaline, so a simple manure tea should suffice? Good chicken health, less effort, finely crushed mineral particles, balanced NPK, high bacterial load. Surely??

    *boil egg shells if concerned about spreading pathogens to chickens.

  7. Thanks for the thoughtful insight, suggestions and discussion!

    We are in agreement that creating mineral, nutrient-rich, and diverse soils is the best way of delivering food to plants. Our composting practices (something we’ll be posting about on our blog in the near future) rely on and use Geoff Lawton’s and other agriculturalists’ techniques of expanding nutrient diversity as much as possible to cover the wide variety of food requirements for different plants.

    Like Ben and Jason mention, we are dealing with nutrient-deficient tropical clay. The land we’re restoring has been overgrazed and eroded over nine decades of mismanagement. It’s well documented that foliar application of nutrients is a faster, more direct manner for uptake. It is a higher-energy input and time investment to prepare the solution, but the needs are demanding enough to warrant it for the short-term. As we build up our soil through a combination of mulch, compost applications, polyculture, and nitrogen-fixing ground covers, we’ll hopefully be able to scale back our use and reliance on the eggshell toasting.

    George, I’ve many times longed for a food processor to grind the eggshells. The quantity of shells we collect (upwards of 2,000/shells/week) demands an industrial-sized processor, but access to such quality machinery is a bit tough to come by in our isolated location in Iquitos and Mazán. But, I’m putting it on my list to track one down!

    Adam, that might be a solution regarding feeding the eggshells to the chickens, but I still think it’d be better to put the shells into a compost or crush well and put in a wormbin for them to use as a digestion grinding aid. And we are also using a worm & manure tea for foliar applications as well.

    We will share our results from the eggshell solution trials with anyone interested as they become available. Also, if anyone has experience with calcium delivery to plants in the humid tropics, please contact us through our website with any information!

    Happy growing!

  8. hmmp!your product is great but i want to ask more information and i would like to ask what is the recommended rate of calcium as foliar spray in application per hectare? TNX AND GOOD DAY!

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