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Good Growing

Using Eggshells in the Garden and Compost

Easter, the holiday when I question my love for hardboiled eggs. Don't get me wrong; I love to sit around the table with my kids to dye Easter eggs and then hunt for those same eggs on Easter morning. By the end of the festivities, we are typically left with two dozen hardboiled eggs. Eating a plain hardboiled egg can only be done so many times. Often we turn Easter eggs into egg salad for sandwiches and perhaps some deviled eggs. By the end of our weeklong egg-o-thon, I need a break from eggs.

Once we consume the hardboiled insides, what remains are the leftover eggshells. So what good is an eggshell to a gardener?

For years, eggshells have been recommended as an amendment to soils and containers due to their high calcium content. Some gardeners who grow tomatoes swear by adding six or more eggshells in the planting hole, with the idea that the extra calcium will reduce blossom end rot of tomato fruit. Other gardeners use compost their eggshells to add calcium to their finished compost.

So do eggshells make a difference? Or is this egg wash? The answer – yes it works, but there is one critical step most gardeners are skipping.

Calcium carbonate is what gives the eggshell the strength necessary to protect egg within. Most home composters who toss eggs in the pile will find everything nicely composted, except there will still be hunks of eggshells visible in the finished compost. Gardeners could pull out their tomatoes after a growing season and likely find those very eggshells in the planting hole, in the same condition as they were when they were first planted. The lack of decomposition indicates the bulk of the calcium remains locked in the eggshell and is not available to plants.

How to Use Your Eggshells

The trick is to grind up the eggshells. The smaller the particle size, the better. A study from Alabama Cooperative Extension compared coarsely ground eggshells (crushed by hand) to finely ground eggshells (resembling a fine powder), along with a comparison to pure calcium Ca(OH)2 and agriculture lime. The Alabama study revealed the coarsely ground eggshells "were not much better than nothing at all." However, the finely ground eggshells performed just as well as the pure calcium, both also outperformed the agriculture lime. (Mitchell, 2005)

Coffee grinders work well to crush the eggshells into a fine powder, though you may want to invest in a cheap garage sale coffee grinder for your eggshells. I utilize my ground eggshells in my worm bin. The extra grit in the worm bin assists my worms in digesting the food scraps through the grinding action that takes place in their crop (similar to a chicken). You can also spread ground eggshells on the outdoor compost pile, in tomato planting holes, or around the garden and landscape if a soil test reveals a deficiency in calcium.

Don't have a coffee grinder but still have an abundance of eggshells? Another trick is to boil 10 to 20 eggshells and then let the concoction sit overnight. The next day strain the eggshells out of the water, and you have liquid calcium solution. Each eggshell adds four milligrams of calcium. Two cups of the solution per plant should be adequate. Apply about every two weeks. (Gillman, 2008)

Eggshells can be valuable to gardeners who need to manage soil calcium levels and are beneficial additions to compost, namely worm bins. Eggshells ground to a fine powder yield the quickest results, while large chunks of eggshells will take at least a year to break down making their stored calcium plant available perhaps the next growing season.

Thankfully, there is a use for all these eggshells! Now I need to hunt for recipes on what to do with all these hardboiled eggs.