Using Eggshells in the Garden

Holidays have a way of dredging up old memories, for example my Swedish grandmother's method of putting a dried, crushed eggshell into her old percolator along with the coffee grounds. My grandmother's people came from the north of Sweden where nothing is wasted, but did putting eggshells in the coffee make it better?

Actually, it probably did. Eggshells are made up of primarily of calcium, which readily leaches into warm, acidic liquids like coffee, which has a pH between 4 and 5. Like a low dose of lime, the eggshells probably raised the pH slightly and mellowed its flavour. They also probably enriched the coffee with dietary calcium, which Grandma Ruth would have loved had she known about it.

Indeed, recent research has shown that consuming eggshell powder as a dietary supplement increases the formation of both cartilage and bone in people with osteoporosis, and can significantly strengthen bones of post-menopausal women.

Using Eggshells in the Garden

The calcium from eggshells is also welcome in garden soil, where it moderates soil acidity while providing nutrients for plants. Eggshells contain such an abundance of calcium that they can be used almost like lime, though you would need a lot of eggshells to make a measurable impact. By the time they are well ground, it takes 150 eggshells to make a cup of coarse eggshell powder. I should know. I make precious pulverised eggshells and use them as a dietary supplement for selected plants. Tomatoes that have a handful of eggshell meal worked into the planting site are not likely to develop blossom end rot, and plenty of soil calcium reduces tip burn in cabbage, too.

I have heard ten thousand times that eggshells placed on the soil's surface deter slugs, but when I tried it the slugs just laughed. When some Oregon slug slayers set up two actual tests, they found that a ring of eggshells stimulated slug feeding rather than stopping it (see photo at right). It is a myth that eggshells deter slugs.

Yet eggshells are quite useful in adding calcium to homemade fertilisers, or you can simply make calcium water by steeping dried eggshells in water for a couple of days, and then using the strained water for your plants, including houseplants. Plants that haven't been repotted for some time often perk up quickly when given a good drench of eggshell water.

Clean Eggshells are Safe Eggshells

Eggs are known carriers of salmonella, which should not be present on uncracked eggs that have been well washed, but you never know. Unless the only place the eggshells are going is into the compost bucket, I rinse them well and let them dry in a sunny windowsill.

The dryness should kill any salmonella present, but if you want to store ground eggshells that are safe for you or your dogs to eat (eggshell powder is used as a calcium supplement for dogs, too), sterilise them in a 200°F (93°C) oven for 30 minutes. You can then pulverise the dried eggshells using a mortar and pestle, or let a coffee grinder do the work for you. Stored in an airtight container, crushed eggshells will probably last forever.

By Barbara Pleasant