Growing Weed with Eggshells: Natural Fertilizer, and More

Last updated: 10 November 2021

Growing Weed with Eggshells

Your cannabis plants require a good balance of macro and micronutrients to thrive. Calcium and magnesium are the most common micronutrient deficiencies for weed, which is the reason for the hefty price tag associated with commercial cal/mag supplements.

Fortunately, you can create your own inexpensive, nutrient-dense supplement at home with just a couple of household items and ingredients – and it really isn’t difficult to do. In this article, we’ll show you how to make your own supplement using eggshells, vinegar, and molasses, as well as reveal a nifty method of turning eggshells into seedling trays.

Can I Add Eggshells Straight to Soil?

Eggshells can be a great addition to acidic grow mediums, as they raise pH levels. However, when it comes to calcium absorption, it takes a long time for eggshells to become bioavailable if placed directly into soil. A very long time, in fact. And remember, your cannabis plants will normally be ready for harvesting in less than 4 months from germination, or sometimes much faster. This means that eggshells placed directly into soil will have almost no benefits for your plants. Moreover, they will only break down in acidic soils of less than pH 6.8.

We say almost no benefits because although they won’t provide anything in the way of nutrients to the soil, they will work to increase soil aeration and drainage. For the plants to utilize the nutrients, we first need to change the chemical composition of the eggshells, turning them into a homemade cal-mag fertilizer. Here’s how to do so.

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Home-Made Cal-Mag Fertilizer from Eggshells

An empty eggshell is composed of 95% calcium carbonate, but it also contains other vital nutrients like magnesium and phosphorus. You will first need to apply some heat to your eggshells, which changes the chemical composition from calcium carbonate to calcium oxide. This may sound like something only a scientist is capable of, but as you will soon see, using eggshells as cannabis fertilizer can easily be accomplished by anyone with a few household items.

Ingredients and Equipment

  • 12 eggshells
  • Frying pan
  • Stove
  • Coffee grinder or mortar and pestle
  • Apple cider vinegar (or white vinegar)
  • Fine mesh sieve
  • Molasses
  • Large bowl or pot
  • Large jar

Step 1

After cooking your breakfast, wash your eggshells both inside and out. Sit them somewhere warm to dry for a day or two.

Step 2

Once dry, crumble the shells directly into a dry frying pan (no oil required). Place the frying pan onto the stove on medium to high heat and toast until the shells start to turn brown or black.

Step 3

Once the eggshells have cooled, use a coffee grinder or a mortar and pestle to grind the shells into a fine powder. Transfer the powder to a large bowl.

Step 4

Put your pot or bowl in the kitchen sink or bathtub. You will now cover the eggshells with vinegar. We’ve specified apple cider vinegar because it contains additional nutrients and benefits for your plants, but any vinegar you have available will do the job. You’ll want to add the vinegar slowly at first, as it’s going to cause a chemical reaction that will fizz up quite rapidly.

Step 5

The chemical reaction will continue for a good few hours, so leave the bowl to do its thing, preferably overnight. You want all the fizzing to stop before proceeding to the next step.

Step 6

Transfer the mixture to a jar and seal the lid, making it air-tight. Keep this aside for a couple of days for the product to ferment. After this time, filter the liquid through a fine-mesh sieve into a jar.

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How to Use Homemade Cal-Mag Fertilizer

How to Use Homemade Cal-Mag Fertilizer

This is a highly concentrated calcium-based solution that will need to be watered down and have the magnesium added separately. This comes in the form of another cheap household product: molasses.

Add one tablespoon of your fermented eggshells to a bottle. Add one tablespoon of molasses. Then add one gallon (3.8L) of water to the bottle and shake well. Check the pH. Adjust to 6.5 using vinegar, sodium hydroxide, or pH-up or down. You can now go ahead and feed this to your plants as you would normally.

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Bonus Trick: Using Eggshells to Start Weed Seedlings

There are no limits to how imaginative you can be with your cannabis grow. You can even plant your seeds inside an eggshell, saving you further money on small pots or seedling trays. If you use eggshells for cannabis seeds, Mother Nature will thank you too, as it has the added benefit of cutting down the amount of plastic we consume. Here’s how to go about it:

Step 1

Take an egg and gently tap on the pointy end with a teaspoon. Peel away a small amount of shell to open up the seedling pot. Gently rinse out the egg.

Step 2

You can put a single hole using a needle or a drawing pin on the underside of the egg to help any excess moisture drain, although we’ve found that this isn’t entirely necessary – it comes down to grower preference. If you choose not to use this hole, just be careful not to overwater your seedling.

Step 3

Place the eggshell back in the egg carton with the larger hole facing the top. Using a teaspoon or a tablespoon, carefully fill the shell three-quarters full with soil.

Step 4

Using some kind of tool – a small screwdriver works well here – dig a small hole in the middle of the soil and place your cannabis seed directly into that hole. Gently cover it with some more soil and add water. A tablespoon could be a useful watering implement for this, as you won’t require much.

Step 5

When you’re ready to transplant, remove the eggshell from the carton. Holding it between two fingers, gently tap the bottom of the shell with a spoon until it cracks. Peel away the cracked shell to reveal your seedling’s root system. Now that this has been done, you can submerge the eggshell directly into a bigger pot.

Should I Use Eggshells for Cannabis?

If you’re an egg consumer or you want to save money on expensive commercial supplements, we highly recommend making your own calcium-magnesium fertilizer at home. It requires only a few ingredients, a couple of household items, and just a little bit of patience.

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Useful information, well presented as usual. I have found that you really cannot ad to much calcium in the form of eggshells, because plants will only take up what they need. I do this all the time if I grind the shells to fine powder before I give them the egg shells
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