Eggshells in the garden: myth or reality?

Some shamans can fix your computer and bring back your loved one in less than 48 hours. According to many gardeners, eggshells are just as good as any other fertilizer. They're said to turn your soil into fertile earth, repel slugs, and cure diseases. Should we really believe this?

Eggshells are said to be an excellent fertilizer

We all dream of an effective, organic, and free fertilizer – Photo by Ivan Radic / Flickr

Eggshells are said to be an excellent natural fertilizer. At least that's what my grandmother, my neighbor, and half the gardeners on the internet say. To grow healthy plants, all you have to do is grind the eggshells into a powder and then, depending on your preference:

place them at the base of the plants;
place them at the base of the plants;
mix them into the soil.

At first glance, using eggshells to fertilize your plants seems like a pretty good idea. In fact, a chicken eggshell is 95% calcium carbonate, crystallized as calcite. And as is well known, plants need calcium to grow.

But the reality is more complicated. Eggshells take a long time to decompose. In soil with a typical pH—such as that found in our gardens and vegetable patches—it takes several hundred years for an eggshell to turn to dust. In Israel, archaeologists have found chicken eggshells over 2,600 years old that hadn't decomposed yet!

So you'll need to be patient if you want to fertilize your plants with eggshells. It will take several centuries before your roses, peonies, tomatoes, and eggplants benefit from the calcium released by the eggshells.

Don't like waiting? Use a calcium-rich fertilizer instead to feed your plants, and set a reminder inthe Monstera app to make sure you don't forget.

Eggshells can neutralize acidic soil

Certain crops can help alter soil structure – Photo by John Moore / Flickr

The high calcium content of eggshells can also help adjust soil pH. Crush the shells and bury them to transform acidic soil into a more hospitable environment.

Again, the main flaw in this plan is the slow decomposition process. While acidity speeds up decomposition, you'll still have to wait two to three years for your eggshells to break down in very acidic soil with a pH of 4…

But even if you're very patient, you'll face another problem: the quantity of eggshells needed. To permanently alter your soil's pH, you'll need hundreds or thousands of eggshells, depending on the size of your garden!

Fortunately, there are more effective solutions for improving your garden's pH. If your vegetable garden is too acidic, for example, you can amend the soil by adding calcareous materials (dolomite, wood ash, agricultural lime, etc.) or by liming the soil. Finally, planting millet or lupine helps correct the soil's structure and composition.

Eggshells Repel Slugs

Hand-picking is one of the most effective methods for getting rid of slugs and snails

Eggshells are said to be the guardian angels of our vegetable gardens and flower beds. When roughly crushed, they form a natural, impenetrable barrier for slugs and snails. Their sharp texture injures the gastropods, preventing them from reaching our vegetables and flowers.

Many gardeners have believed this gardening myth only to find their lettuce and tomatoes devoured early in the morning. Slugs and snails couldn't care less about eggshells. They secrete a mucus that protects them and allows them to get past this barrier.

If you want to protect your plants from gastropods, forget about old wives' tales. Instead, use a net or slug pellets. You can also set up a dedicated area for them in your garden, complete with shelter and food, to divert them away from your vegetable garden.

Eggshells Treat Peach Blister Disease

Leaf curling is one of the symptoms of peach leaf curl – Photo by Tsaag Valren / Wikipedia

Eggshells are also said to combat peach leaf curl. This is evidenced by the nets filled with eggshells hung from tree branches.

Peach or almond leaf blight is a fungal disease caused by a fungus. Contrary to popular belief, it does not develop when the soil is low in calcium, but rather when the weather is humid and temperatures exceed 10 °C. This is why symptoms often appear in the spring.

Decorating your fruit trees with garlands of eggshells will therefore have no effect. The symptoms and the fungus will disappear in the summer, when rain showers become less frequent and the weather warms up. If you want to effectively control peach and almond blight, opt instead for preventive measures:

plant resistant hybrids and cultivars;
fertilize and prune your trees to keep them healthy and thus less vulnerable;
remove blistered leaves to prevent the spread of the disease.

Eggshells Help Fight Tip Blight

Mulching helps indirectly combat tip rot – Photo by Arpent nourricier/Flickr

Burying eggshells at the bottom of the planting hole for vegetables and tomatoes is said to be a natural solution for combating blossom end rot.

Blossom end rot is linked to a calcium deficiency in certain plants such as tomatoes, squash, and peppers. Supplying calcium through eggshells is said to prevent this condition.

Two arguments contradict this reasoning. First, eggshells take an eternity to release the calcium they contain. Furthermore, in the case of black-bottom, the calcium deficiency is not due to a lack of calcium in the substrate. It is linked to the plants' inability to absorb it. Most often, this problem results from irregular watering. When the plant lacks water, the sap does not reach the fruit, which then rots.

To combat tip rot, make sure your plants aren't suffering from water stress. Water potted plants and those in the ground regularly. Feel free to mulch the soil to keep it moist between waterings.

How can you use eggshells in the garden?

Next topic on the blog: sowing seeds in an eggshell—cute or gross? Photo by Xoyos / Flickr

Would you like to recycle your eggshells in the garden? The best solution is undoubtedly to add them to your compost. You can then use the compost to fertilize your flowers, trees, and vegetable garden. Be sure to crush them into small pieces first to help them break down. Also, make sure they don't make up too large a proportion of your organic waste to ensure they're properly absorbed.

What's more, eggshells make an excellent dietary supplement for chickens! In fact, to produce their calcium-rich shells, laying hens need… calcium. If you have your own chicken coop, crush the shells and offer the pieces to your chickens to enrich their diet.

Finally, some gardeners like to use eggshells instead of plastic seedling pots. All you have to do is empty the egg, poke a hole in the bottom of the shell, fill it with substrate, and plant seeds inside. This technique doesn't offer any added value in terms of gardening, but it can save you the cost of a seed tray and add a quirky touch to your decor.