Egg Shells in the Garden

You’ve heard egg shells can be composted and that your plants need calcium. Before you add crushed or powdered egg shells directly to your soil, read this quick article to learn the best way to get calcium to your plants! Spoiler: Plants CANNOT use the calcium directly from egg shells buried in the garden. They need soil microbes to break it down into a usable form first.

Egg shells absolutely CAN be added to your compost pile! They break down slowly so you’re going to have sharp little egg chip pieces in there for about a year. Many gardeners find it better to let the egg shells dry out, either on the counter for 48 hours or in a 170°F oven for 1 hour before grinding them into powder. Both ways are going to add calcium to your compost. But did you know that plant roots cannot take up the egg shells as calcium?

Plants Cannot Use Egg Shells Directly

No matter how finely you grind the egg shells to powder, your vegetable plant roots cannot take it up. They need tiny soil microbes to break down calcium-containing compounds (like egg shells) within the soil into a form the plant roots can then absorb.

Microbes Required

The egg shells you are composting need microbes to break them down over time into a usable source of calcium. It is okay to add powdered egg shell into the soil around your vegetable plants – the microbes will be able to find it – but it is NOT directly taken up and utilized by the plant roots, no matter how finely the egg shells are powdered.

Egg Shells in the Garden compost — Egg shells, like the white ones shown here, can be composted and soil microbes will break down the calcium into a form plant roots can absorb. If you do not have backyard hens who can eat the shells, this is the next best way to dispose of them!

But the Internet Said So?

An online search will produce dozens of articles suggesting that you put your egg shells directly into the garden. People love the idea of reducing what they throw away and turning food scraps into soil fertility. Egg shells are a valuable source of calcium carbonate. One of the best things you can do with them is feed them to backyard chickens as a source of supplemental calcium. (Yes, chickens should eat egg shells!) If you don’t have chickens, the compost pile is the next best place for them. If you want to invest the time to dry and powder them, that is the only way I would suggest adding them directly to your garden soil. Otherwise egg shell chips need around 12 months in the compost heap where microbes can break them down, enriching the soil with the calcium and trace minerals they contain.

Get Calcium to Your Vegetable Plants Faster

While the soil microbes are working to break down last year’s egg shells into something usable, there are organic ways you can get calcium to your growing plants now. My favorite product is Cal-Mag, which is a foliar feed that rushes calcium and magnesium to mineral-hungry plants, boosting fruit production and quality. Simply add 1 teaspoon per gallon of water in your watering can and wet the leaves. Cal-Mag is absorbed through pores in the leaves. (Affiliate link.)

Blossom End Rot in Tomatoes and Peppers

When blossom end rot strikes your tomatoes and peppers, it can be tempting to overload the soil with bone meal, powdered egg shells, wood ash and anything you can think of that may help. Blossom end rot is caused by a calcium deficiency because there has not been enough water in the root zone so the plant can take up the calcium which is already in the soil around it. It is a watering issue, not a true calcium issue. The fastest way to correct it is to water regularly and use Cal-Mag as a foliar feed (1 teaspoon per gallon of water) so fruit that is beginning to set will not be impacted by blossom end rot. Fruit already experiencing blossom end rot cannot have it reversed.

foliar feeding watering — Foliar feeding your plants with Cal-Mag is the absolute fastest way to ensure they get the calcium they need for the rapidly growing fruits.

Don’t Throw Away Egg Shells!

Egg shells are so useful they really should not be thrown away! Neighbors with backyard chickens would LOVE to have your empty egg shells so they don’t have to purchase oyster shell as supplemental calcium for their hens. Calcium-rich egg shells also have a place in the compost pile where they ensure the compost will forever be rich in calcium. If you have hens and a garden, the hens take priority and should be fed the egg shells, especially during the spring months when they are laying heavily. As laying slows down towards the autumn molt, egg shells can be split 3/4 with the hens and 1/4 to the compost pile.

Chicken manure also contains calcium as well as nitrogen, phosphorus, potassium, magnesium, sulfur and micronutrients. Green leafy weeds and spinach scraps also contain calcium so you are NOT robbing the compost pile if all the egg shells go to the hens.

Egg Shells in the Garden kitchen scraps — The egg shell halves in this image will need over a year to break down.

Too Many Egg Shells in the Compost?

Egg shells break down S-L-O-W-L-Y, with half an egg shell needing over one year to fully break down. Compost with too many egg shells won’t be uniformly brown but instead look unfinished with lots of light colored, finger-poking sharp fragments. Crushing egg shells into smaller pieces helps combat this issue.

Fun Fact: Egg shells in compost are neither a “brown” nor “green” component. They are 94% calcium carbonate which makes them primarily a mineral.

Recipe for Turning Egg Shells into Water Soluble Calcium

Update: I was given a tip for how to use egg shells and vinegar to create water soluble calcium that plant leaves and roots can absorb! Full directions with pictures can be found here. You need 10 chicken egg shells, dried out and ground to a fine powder. You take 2 Tablespoons of the egg shell powder and place it in a bowl with 2 Tablespoons of vinegar. Mix with a non-metal utensil (silicone or wood) a few times per hour until the mixture stops foaming. The calcium neutralizes the vinegar into plain water and you’re left with water soluble calcium concentrate. You’ll combine the 4 Tablespoons of the egg shell & vinegar mixture with 1 gallon of water, shake to combine and then use it to water your plants. Much faster than waiting for egg shells to break down in the compost pile and cheaper than buying Cal-Mag!

Hens First, Compost Pile Second, Soil Amendment Third

I hope this quick article has helped you understand the role of egg shells in the garden and why they may benefit your backyard hens the most and the compost pile next. And if you buy eggs in natural colored paper pulp cartons with no glossy labels, they can be torn into smaller pieces and go in the compost pile, too!