An essential Korean Natural Farming input for stronger, healthier plants
Calcium plays a crucial role in plant development—especially in strengthening cell walls, promoting healthy root development, and preventing common disorders like blossom end rot. But not all calcium is bioavailable or easily absorbed by plants. That’s where Water-Soluble Calcium (WCA) comes in.
Used in Korean Natural Farming (KNF) and organic gardening, WCA is an inexpensive, highly effective foliar feed made from nothing more than eggshells or oyster shells and vinegar. It delivers plant-ready calcium directly where it’s needed most.
Let’s break down how to make WCA at home, how to use it, and the science behind why it works so well.
🌿 Why Plants Need Calcium
Calcium is vital for:
- Strong cell walls
- Healthy root development
- Regulation of nutrients like potassium
- Prevention of blossom end rot in tomatoes, peppers, squash, and melons
Most soils already contain some calcium, but much of it is insoluble, meaning plants can’t absorb it. That’s where WCA becomes a game-changer—it delivers immediately bioavailable calcium through a foliar spray.
🧂 What You’ll Need
Ingredients:
- Clean, dry eggshells (or oyster shells)
- Raw vinegar (apple cider vinegar or brown rice vinegar preferred)
Tools:
- Glass jar with lid (do not use metal lids)
- Paper towel or cloth (for covering during off-gassing)
- Rubber band
- Strainer
- Clean bottle or jar for storage
🧪 How to Make Water-Soluble Calcium
Step 1: Prepare the Eggshells
- Collect at least 10-12 clean eggshells.
- Bake them at 200°F (95°C) for about 10–15 minutes to dry them out and make them more brittle.
- Crush them lightly with a mortar and pestle or the bottom of a jar.
Optional: You can also use oyster shells or bones that have been baked and crushed, which provide similar results.
Step 2: Add Vinegar
- Place the crushed shells in a glass jar, filling about 1/3 to 1/2 full.
- Slowly pour in raw vinegar until the shells are fully submerged.
- The reaction will fizz and bubble—this is the acetic acid in vinegar reacting with calcium carbonate to extract calcium acetate, a plant-available form of calcium.
Step 3: Let It Sit
- Cover the jar with a paper towel or cloth and secure with a rubber band (to let gases escape).
- Leave the jar at room temperature for 7 to 10 days.
- Stir or swirl lightly once a day.
When the bubbling stops, the calcium has been fully extracted.
Step 4: Strain and Store
- Strain out the solids with a fine mesh strainer or cheesecloth.
- Store the liquid in a clean, sealed jar or bottle.
- Keep in a cool, dark place. It will stay potent for 6–12 months.
🧪 The Science Behind WCA
The key chemical reaction:
CaCO₃ (calcium carbonate in eggshells) + CH₃COOH (acetic acid in vinegar) → Ca(CH₃COO)₂ (calcium acetate) + CO₂ + H₂O
This reaction turns the otherwise insoluble calcium into calcium acetate, which is readily absorbed by plants when applied as a foliar spray.
🌿 How to Use Water-Soluble Calcium in the Garden
💧 Dilution Ratio:
- Mix 1 teaspoon WCA per 1 quart (1 liter) of water
- For larger batches: 1 tablespoon per gallon of water
✅ When to Use:
- During flowering and fruiting stages (calcium is especially critical here)
- After transplanting, to reduce stress
- Once a week as a foliar spray or soil drench
🚫 When NOT to Use:
- Avoid during early vegetative growth—too much calcium early on can interfere with nitrogen uptake and delay plant growth.
🌾 Benefits of Using WCA
- Prevents blossom end rot
- Strengthens stems and leaves
- Improves fruit firmness and shelf life
- Encourages proper nutrient uptake
- Aids in root and shoot development
- 100% organic and safe
🛠️ Pro Tips
- For a stronger solution, use bone-derived calcium, but this must be well charred.
- Always use raw, unpasteurized vinegar—this maintains beneficial microorganisms.
- Do not combine with other acidic or nitrogen-heavy foliar sprays.
- Apply early in the morning or late evening to prevent sunburn.
🧂 What to Do with the Leftover Shells?
After straining, you’ll have soft, vinegar-soaked shells left over. Don’t toss them! Here’s how to reuse:
- Dry and crush them to add to compost or top-dress garden beds.
- Mix into the chicken coop bedding as a calcium boost.
- Add to worm bins in small amounts.
🌎 Final Thoughts
Making Water-Soluble Calcium at home is an easy, affordable, and powerful way to supercharge your soil health and plant growth without relying on store-bought products. It brings together two simple ingredients—vinegar and eggshells—into one of the most powerful KNF inputs available.
Whether you’re battling blossom end rot, trying to boost fruit development, or just want to give your garden a natural edge, WCA is the organic tool every grower should have on hand.