Saving Eggshells For Garden Use? -- Leave 'em Whole. . . or Half Whole, I Mean!
Leaving Eggshells Whole in Compost
To crush or not to crush?
I understand why some gardeners smash eggshells into smaller pieces or put them into a coffee grinder to make them into grainy particles. They want the minerals to break down and become part of the soil. The shells of eggs have not only calcium (in the form of calcium carbonate which is great for sweetening acid soil) but nitrogen and phosphorus. Shells can also add various other minerals such as copper, zinc, manganese, potassium, and other good stuff in trace amounts. Of course you want those helpful nutrients in your compost and then in the garden bed for your plants to use.
But my experience is that the whole eggshell -- well, of course it's really a half eggshell -- disintegrates nicely when left whole. And there are a couple of good reasons to leave the cup shape of a broken shell.
Rinsed half eggshells drying on the kitchen windowsill
The shells darken, soften & fall apart on their own
I'd turn back if I were you, slug
If an eggshell is broken into six or seven big pieces, you've got a barrier to keep cutworms and other creepy crawlies from reaching the stems of your plants. Just place a few of these rough-edged pieces on top of the soil near your tomato plant's stem. The sharp edges of the shell are too much for the soft-bodied slugs. This is the garden equivalent of topping a cement wall with embedded broken bottles or a string of barbed wire. Deterrence is key.
This worm was napping till I woke it up
Worm condo! Worm nursery!
Many people who raise composting worms put eggshells into the worm bin. Some grind up the shells fine and add that to a "worm fattener" mix, with cornmeal, oat flour, baby chick food, and the like. The calcium carbonate in the shell make the worm's outer skin tougher. I believe the calcium is leaching out into the soil/compost because the shells soften in the compost pile till jus the inner membrane is holding a thin layer of shell together. So I think the worms get what they need without crushing the eggshell.
If there are redworm pals hanging out in your compost bin, they like to curl up inside broken eggshells. Maybe it's safety inside curved walls. Maybe the shell retains moisture, which worms like. Maybe they can absorb nutrients that are moving from the shell to the compost. Whenever I need to take worms out of my compost bin, the first place I look is inside a half-shell with a bit of dirt and ground coffee and a bit of worm casting in it.
Another redworm farmer has confirmed that leaving the "cups" of egg shell is not only a worm hangout, but a worm nest. They like to lay their eggs in there, and a worm bin needs eggs to hatch and wormlings to mature to take the place of older adult worms in the population.
I don't crush, but I do rinse
A May 31, 2013 article by Beth Clawson on the Michigan State University Extension website (http://msue.anr.msu.edu/news/adding_eggshells_to_compost) states that eggshells are safe to add to yur compost pile. Some people worry about salmonella. I've never had any issues with using them in my garden compost pile or in the worm compost bins.
My mother, who had some nursing training, warned me when i was young about using cracked eggs as salmonella bacteria could go from outside an egg into the interior if the shell was broken. For that reason, I don't cook cracked eggs and I would not add them to my compost pile, even though the MSU article says the heat from the compost and the samll volume of the egg would surely keep the bin or pile contents healthy.
I also rinse the eggshells before I add them, and then let them dry. I know bacteria need dark, damp conditions to flourish, and a couple of nice dry sunny days seems like a good place for an eggshell to be. I have heard that some people use paper egg cartons to hold the drying shells. It seems to me that the shells would stick to the paper but I guess if you're composting the whole thing anyway, that wouldn't matter. And the absorbent cardboard may dry the eggshell as well as an afternoon or two in the sun. Using the carton might look tidier if you live with people who are not as compost-loving as I am.
Thank you for reading this!
I really like being part of a community where I can read posts by others, who share their real-life experiences with growing perennial vegetables, urban farming, raising culinary and medicinal herbs, and other topics which interest me. A book on green living or homesteading can offer lots of ideas, but there's a difference to me between a great picture of a fabulous castle of a chicken coop and then the day-to-day adventure of raising backyard poultry. And of course where else could I share my many thoughts about the joy of composting worms and wet eggshells on my windowsills?!