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Don’t throw away your eggshells. You can make a great garden supplement from them that will add a calcium boost to your plants.
The main reason that we want to use eggshells in the garden is their calcium content because of its beneficial effects on plants. Calcium is a macronutrient that goes into making the walls of plant cells and a little more calcium will make them stronger and thicker. That means that they’ll be more resistant to attack. It is particularly useful for Tomatoes and Capsicums as its presence in the plant at appropriate levels helps prevent Blossom End Rot.
Eggshells are roughly 40% calcium, in the form of easily accessible calcium carbonate. In addition to calcium eggshells also contain protein and small amounts of other minerals, including strontium, fluoride, magnesium and selenium.
Vinegar is a great way to extract minerals from many substances and the resulting liquid is shelf stable for a long while. That means you can store it in a cool dark place for use later. It is perfect for extracting calcium because the acid in vinegar breaks the calcium free of its bonds. Calcium is also water soluble but the extraction process (usually boiling and letting the brew sit) isn’t as fast nor as complete.
Wash and roast your eggshells. Roast them at around 150 degrees C for 20 mins or so to dry off the organic material. If you don’t remove the membrane and other contaminants, they can break down in the vinegar and spoil it.
Add vinegar to the eggshells at a ratio of about 4:1 The ratio of vinegar to eggshells is pretty arbitrary and I’ve settled on one of 3 to 1 or 4 to 1 depending on how much vinegar i have. I usually use home made Apple Cider Vinegar or fruit vinegars but at the moment, I don’t have any around because my ACV mother got a bit sick and I’m starting a fresh one. I like these vinegars because they’re practically free but you can always use white vinegar, it works well but the resultant brew will be lacking some of the other goodies that ACV contains.
Stir the mix to make sure the vinegar reaches all of the eggshells and leave for a week, stirring occasionally until any bubbling stops. Leave the lid off of the container that the reaction is happening to let the gas from the bubbles (carbon dioxide) escape in or you could end up with a mess when you open it.
After a few days to a week, strain out the eggshells and bottle and store the solution. You can leave it for longer to more fully extract the mineral content of the shells but I’ve found that at this stage, its more effective to strain and add fresh vinegar to the leftover eggshells. It’ll bubble a bit and you can repeat the process. Add any subsequent vinegar extract to the original batch.
Use your extract as a foliar spray on leaves or a drench for the roots of plants either as a regular part of your fertilising routine or as an emergency amendment for plant health problems.
You don’t need to use much of the vinegar extract. Calcium is a micronutrient afterall. I use 1 tablespoon in a watering can of water or 1 teaspoonful in my 2 litre sprayer for a foliar spray. Some sources, say that you can use less than this but I’ve found that these are pretty good amounts.
Nutrients work synergistically so, as an extra boost, I usually add a couple of drops of Seasol to whichever vessel I’m using to make it a bit more potent and broad spectrum when using it to remedy plant health issues.