Despite the fact that eggshells may be beloved by home cooks, they are the bane of many composters. I will always remember my disgust when I harvested my very first batch of compost.
I was delighted to find that all of my food waste and garden trimmings had magically transformed into a gorgeous brown, humus-like substance, with the exception of lots and lots of eggshells.
It worked for me, and now I no longer find big chunks of shell in my compost. You do not need to do it either.
Aside from how and when to add them to your compost, I’m also going to talk about other ways to use them as a soil amendment, as well as whether or not they work as a pest deterrent.
Eggshells as Food Waste
It takes up a lot of space when you don’t break down eggshells, whether you’re composting or throwing them away.
The oval shape of the boxes, how perfect for containing their contents, doesn’t flatten out well in the trash, unless you crush them first.
Adding up the weight of all these oval wonders each day means nearly a million pounds of waste taking up space in landfills.
There is plenty of upside to being creative with these empty egg cartons, and it’s a great opportunity for home gardeners to get involved.
Eggshell Nutrients
Before we discuss how to repurpose this abundance of food waste, I think it would be helpful to demonstrate exactly how much food waste is being discarded at a rate of nearly a million pounds every single day.
Here’s what the average eggshell is comprised of:
- 95% calcium carbonate
- 0.3% phosphorus
- 0.3% magnesium
- Traces of sodium, potassium, zinc, manganese, iron, and copper
I feel like it would be so inconvenient to throw all those nutrients away, doesn’t it?
If you can use them instead of a garden product you might otherwise have to purchase, like agricultural lime. In fact, a study presented at the 2006 Iowa State University Integrated Crop Management Conference by extension field specialists John Holmes and Paul Kassel found eggshells to be an effective means of reducing soil acidity, on par with agricultural lime, which is mined from limestone.
Despite what some may believe, repurposing this kind of food waste isn’t only a DIY hobby popular among home gardeners.
Ground eggshell meal is listed as an organic fertilizer “generally acceptable under the [rules of the USDA National Organic Program (NOP)] for commercial organic farmers,” as described in the North Carolina Extension Gardener Handbook published by North Carolina State University, with an average analysis of 1.2-0.4-0.1 (NPK).
While eggshells are relatively low in phosphorus, nitrogen, and potassium, the takeaway is that this waste material has enormous value as an excellent source of calcium, being used as a soil amendment to both feed plants and neutralize acidic soil.
Use as a Soil Amendment
How can you tell if your garden will benefit from calcium addition? You may even want to do a soil test to determine how much calcium your soil contains.
In acidic soil, adding calcium can help depending on what you want to grow. There are cases when acidic soil is preferable, such as in case of blueberries and related ericaceous plants. Therefore, adding an alkaline amendment such as calcium is not necessary in that case.
Adding calcium to your soil may or may not be a good idea based on the results of your soil test. If you are growing tomatoes and other foods that may be susceptible to blossom-end rot, eggshell calcium may be a great aid at planting time.
In a paper published in the March 2016 issue of the International Journal of Innovative Research in Science, Engineering and Technology , Madhavi Gaonkar and A. P. Chakraborty from Dr. Babasaheb Amebedkar University in Maharashtra, India, described their research on using eggshells as a calcium supplement and fertilizer.
According to these researchers, powdered eggshell is “probably the best natural source of calcium.” If used properly, this amendment could help balance soil calcium levels, preventing blossom-end rot.
Charles C. Mitchell, extension agronomist with the Alabama Cooperative Extension also studied adding this food waste to the soil in a farm setting to neutralize soil acidity.
In his opinion, if eggshells were not ground to a fine powder, smaller than sand, adding crushed eggshells to the soil would have no benefit.
As a result, he was able to produce a calcium source for plants that was more efficient than agricultural lime, as well as a source which was readily available to them.
It is generally true that large pieces of shell don’t break down quickly enough for use as amendments or soil sweeteners. However, when ground into a powder, they bind to the soil, becoming more readily bioavailable and altering its pH.
The calcium in ground shells has other uses besides preventing blossom-end rot. For instance, it can be used to prevent apple cork rot, or as a substitute for lime in your lawn.
Nonetheless, it would be beneficial to learn more about how plants utilize nutrients and minerals before you start scattering calcium across your garden. This will help you use calcium as a soil amendment wisely.
Use in Compost
Eggshells can be composted for a variety of reasons, including soil amendment and sanitary disposal. We suggest you compost them rather than throw them away if that’s not on your agenda. The first, as discussed above, is to prevent these materials from ending up in landfills.
Food waste breaks down much slower in landfills than in composting piles, largely because landfills are sealed off, anaerobic environments.
As an example, anaerobic decomposition has a bad odor and is less efficient than aerobic decomposition, which is found in a well-maintained compost pile where aerobic microbes flourish.
Food waste is actually turned into nitrogen, phosphorus, and magnesium by aerobic microbes. This provides excellent material to grow more food!
When you compost at home using an anaerobic process, such as bokashi, you will need Lactobacilli bacteria to kickstart the fermentation process, so the shells will dissolve just fine.
You might also compost your eggshells in order to make the soil more attractive to earthworms, either in the compost pile or in your vermiculture bin. Earthworms need grit to break down their food, which eggshells provide in abundance.
No matter if you don’t have a worm bin, you will eventually have earthworms living in your compost pile and in your soil. You can fulfill their needs by including some shell debris for them.
Adding eggshells to your compost pile will make your finished compost smooth and dirt-like, preventing large pieces of shell from becoming tangled in the texture. Composting whole eggs is generally not advisable since the smell may attract rodents.
It will also make it easier for the earthworms to utilize the material as grit if you grind it before adding it to your compost bins or worm bins.
Use as Seed Starting Containers
An eggshell can also be used as a container for seeds, which is another innovative gardening use.
It is possible to upcycle your kitchen waste through this method, but there are certain limitations and preparations you will need to make before getting started.
Plants that grow quickly, such as tomato seedlings, will soon outgrow these small containers. This method is best for starting seeds in small and low-growing containers.
However, when starting tomatoes from seed, if you do, you will want to have larger nursery pots on hand in case you need to transplant them within a couple of weeks after they sprout.
In addition, it is not advised to repot most transplants repeatedly because this can stress them and damage their roots. On the other hand, plants with low growth rates, such as thyme, cucamelons, and certain succulents may grow in eggshells.
It’s best for seeds to be started in sterile containers, so if you decide to use eggshells as seed pots, the first thing you want to do is make sure the shells are thoroughly cleaned. Thick shells are easier to clean without breaking than thin ones.
If you’re buying eggs from a farm, ask the farmers if they have eggs from younger layers. Generally, the shells of younger layers are thicker, while the shells of older layers are thinner.
You can gently wash out the eggshells with warm, soapy water – or boil them in hot water for a sterile growing environment. Meanwhile, young seedlings require a sterile growing environment and drainage.
Assuming you are able to successfully clean your eggs without cracking them, poke two or three small holes in the bottom of each eggshell so that the seedlings have well-draining soil. Metal paper clips are good for this.
When planting your seedlings, you should keep in mind that whole eggshells don’t break down very quickly – at least not fast enough for their roots to expand into the soil.
Before planting the seedling, remove the shell by either lifting it out with a widger or small spoon, or cracking the shell to remove it. If you want more guidance on growing annuals from seed, follow the directions in our guide.
Use as a Pest Deterrent
Another way to use readily available food waste in gardening is to pile crushed shells around the bases of plants as a barrier to deter some soft-bodied pests.
If you sprinkle crushed eggshells around your crops, you may be able to repel cutworms, nasty caterpillars that love to nip the heads off your fragile seedlings.
In order to defend against cutworms, one way to block their access is to place collars around seedling stems. Cutworms prefer the undersides of young seedlings, so collars block their access.
T. J. Martin at the Cochise County Master Gardeners office, crushed eggshells are also an effective deterrent against cutworms when a layer is scattered around the stems of sensitive young seedlings.
In our experiment, we used a paper plate as the testing ground. The slugs were placed in the center of the plate surrounded by a barrier of crushed eggshells.
Our next concern was whether the sharp edges would keep the slugs seated in the center of the plate – or if the slugs would keep moving anyway.
As a second attempt, we put pennies in place because copper is also supposed to be a slug-deterrent. However, neither barrier worked.
So I think it’s still uncertain whether this DIY solution will work to eliminate slugs in the garden, but using crushed eggshell pieces as a mulch around your plants certainly won’t hurt them – they won’t even change the soil’s pH over the short term.
What About Salmonella?
Slugs are unpleasant, but salmonella is even worse.
My recipe for in-ground eggshells includes baking them in the oven to dry them out before grinding them. This practice accomplishes two things at once – it removes the sticky, inner membrane as well as killing salmonella.
You only need one second of moist heat at 170.6°F to kill salmonella bacteria. By using oven-drying, your eggshells will be exposed to temperatures higher than that for a longer period of time, so salmonella concerns can be put to rest.
You’ll instead have more time to think about other important things – like how you’ll mark naked gardening day again next year!
How to Make a Soil Amendment
You can now put your salmonella fears at ease by carefully preparing eggshell powder for composting and soil amendments. In a nutshell, you will collect, dry, and grind your eggshell powder.
Collect
Firstly, rinse your shells under the tap so that any raw egg remains will not attract flies, or produce an unpleasant smell.
Place your eggs in an ovenproof dish, such as a casserole dish or cookie sheet. Once the dish is full, you are ready to dry them. The duration it will take to fill the baking dish depends on how often you consume eggs and how many people in your household consume eggs.
When you store them in this manner, don’t bother crushing them – it’ll be much more difficult to crush them after they are dry.
As a matter of fact, I have handled eggshells this way for several years, and in diverse climates ranging from the continental Southern Piedmont to the arid Intermountain West and the humid Pacific Northwest.
In my experience, storing these shells this way has never caused me trouble over the short term – no mold, pests, or odors at all. However, I admit that I bake a lot and my shells tend to get a drying heat treatment every week or so.
The eggshells can certainly be boiled before keeping them if you are concerned about whether they pose a health risk.
If you let the water cool, you can use it as a soil amendment. If you let the shells cook, some calcium will be released, increasing the water’s calcium content.
Dry
When you are done gathering raw shells, wait for your oven to preheat. While it is preheating, place the baking dish full of eggshells into the oven.
If you are going to bake with a glass dish, make sure the temperature is no higher than 350°F – some glass can crack at higher temperatures. Unless you are making your recipe in Pyrex or similar glass that is safe in the 400°F range.
Prior to drying out my eggshells, I store them in a baking dish in the oven. Any time I am preheating my oven and want to do some baking, I just place the baking dish and its contents into the oven, and leave them there to heat for several minutes.
In this way, wet membranes are dried out – although they usually have dried on their own by then – and the salmonella is killed by the elevated temperatures.
Grind
My shells are ground into powder only after sufficiently drying out. I find the best way to do this is to blend them in my blender.
The dried shells can then be ground to a powdery consistency in a blender in small batches. They should be transferred to a mason jar for storage one at a time.
Add the homemade eggshell powder to your soil to incorporate calcium or to neutralize acidity. You can also add it to your compost for further biodegradation.
Alternatively, you can simply store this powder for later use – just be sure to dry it thoroughly before storing it, or add a silica desiccant packet to ensure that it remains dry.
How to Make a Pest Deterrent
When using eggshells as pest deterrents, instead of grinding them into a powder, you should crush them into small, jagged bits instead, after drying them and baking them as described above.
In contrast to grinding them with a coffee grinder or blender, which will create too small pieces to deter pests, crushing them by hand will be more effective.
This can be accomplished by placing small batches in a mortar and crushing them with a pestle, or by placing them on a baking sheet and crushing them with a rolling pin.
Take your crushed shell pieces out to your garden and scatter them around your plants right away. Store them in a jar, or use them immediately.
Breakin’ Up Isn’t Hard to Do
See? It’s not that difficult to break down your eggshells. It is easy to turn the leftovers of your omelets into a compost ingredient or soil amendment by simply drying them out and grinding them.
As far as pest control goes, let’s keep experimenting. What do you think? Have you tried using food waste to improve soil or deter pests? Let us know what you think in the comments.