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The Journal

Water Soluble Calcium (WCA)

WCA is a Korean Natural Farming (KNF) technique for converting the calcium carbonate in eggshells (or alternatively clam or oyster shells) into a form that is made readily available to plants. When applied as a foliar spray this method provides immediate calcium access which promotes plant root growth, fruiting, and normal cell growth (see source).

This method is an alternative to the more commonly used commercial applications of ground limestone (calcium carbonate) or gypsum (calcium sulfate). Each has their own unique benefits, but for the gardener, homesteader, or even small farmer this is a highly cost-effective alternative - particularly if one were raising poultry on site with immediate access to eggshells and/or had a few apple trees to make one's own Apple Cider Vinegar.

This method illustrates the permaculture principal of stacking functions, where otherwise composted eggshells and apples can be put to use in yet another form of available energy.

Plants and Calcium

One of the most common signs of low or inaccessible calcium is blossom end rot on fruits such as summer squash, tomatoes, and pepppers, or tip burn on new or young plant leaves. It's important to note that the uptake of calcium is dependent on correct irrigation. If you know that your soil's calcium levels are sufficient but you're observing symptoms like blossom end rot it could be the result of inadequate, uneven, or over watering. If you're only seeing symptoms on a few plants and not a whole crop it could be because of root damage that is preventing the correct uptake of water.


  1. As I use eggs for cooking or baking I store the cracked shells in a sealed bag in the freezer until I have enough saved up to process. You can also do this with freshly cracked eggs if you have 6 or more eggs being used.
  2. If removing from the freezer, run under warm water to separate. If using fresh eggs or if freezing for later, remove any remaining material or membrane from the shell. Lay on towel or paper to dry before going to the next step.
  3. Break shells into small chunks - the size doesn't need to be too scientific. Alternatively they can be left as halves.
  4. Spread in single layer on a toaster oven baking sheet.
  5. Toast on low setting for a short time (1-2 min), checking the shells at the end of each cycle. They should be a toasted brown color but not blackened.
  6. Once shells begin to look brown, flip the shells and toast again on the other side. When shells are lightly browned they are done toasting.
  7. Place the eggshells in a glass jar, filling 10-15% of the jar with the shells.
  8. Pour Apple Cider Vinegar (ACV) (with the mother, ideally organic) over the shells. Leave around 1" of headspace.
  9. Place jar on a plate or in a bowl where any foam can escape without making a mess.
  10. Set a cap on top of the jar - either a mason top or if it's a recycled jar the original lid - but DO NOT tighten. Gas and foam need to be able to escape or the container can explode.
  11. Store out of sunlight in a cool space for 1-2 weeks. At the end of 2 weeks you should stop seeing any bubbles.
  12. Strain the vinegar into a clean glass jar, keeping the shells for another batch. These processed shells still have plenty of available calcium to extract and this process can be repeated up to 3 more times. Each strained (decanted) batch can be combined into the same final jar.
  13. Label the jar with the name and dates of each decanting. Include any other information you might want, like shell source, ACV source, processing time, etc.
  14. Store out of sunlight at room temperature. It will remain shelf stable for many years.
  15. finished jar of water soluble calcium product


Dilute to 1:1000 with fresh water (~1 tsp per gallon of water). Apply as foliar spray early morning or late afternoon when the plant's stoma are open. Can be combined with FPJ and LAB if desired.

Additional resources