Whether it’s baking, cooking, or just your Sunday breakfast egg – every week, a few eggshells end up as garbage.
But can eggshells be used as fertilizer?
After much research and trial and error, here’s why eggshells make sense as fertilizer, how much, how often, and most importantly, which plants you can fertilize with them.
Eggshells are very good fertilizer especially for plants that prefer alkaline, that is, non-acidic soils. These include, for example, roses, tomatoes, fruit or box trees. Annually, about 3-5 eggshells per square meter can be used as fertilizer by applying them soaked in water as a liquid fertilizer.
Can eggshells be used as fertilizer?
In general, eggshells are very good fertilizer, but for some plants more and for others less good.
But before we take a closer look at these plants and distinctions, we need to understand why eggshells can be used as fertilizer in the first place.
Eggshells consist of about 90% calcium carbonate, so “carbonic acid” lime. This is the reason for the mostly white or partly brown or greenish color of eggshells.
Lime has the property to neutralize or increase the pH-value of soils. In contrast, you can use coffee grounds, for example, to lower the pH and make your soil more acidic.
So when you spread eggshells in the soil, they raise the pH of your soil by doing the following
Increase of the soil pH
Carbonic acid in the soil is necessary for the dissolution of lime. This is produced by the root respiration of the plants. After other intermediate steps, calcium ions, carbon, and water are finally produced, causing the soil pH to rise.
Over time, it is natural for the soil to acidify as minerals are leached out by rain and cultivation.
However, since most plants and vegetables prefer neutral or at most slightly acidic soil, the lime from eggshells indirectly helps improve plant growth and well-being by increasing soil pH.
Improvement of the soil structure
In addition, the calcium ions produced help with cementing. Cementation means that loose and fine soil slowly turns into crumbs in the soil. This improves the soil structure or soil texture as it becomes looser and airier.
Eggshells, however, rot relatively slowly. As a rule, even highly crushed eggshells take about two years to decompose completely.
This is because the chemical processes involved in the decomposition of eggshells take a very long time.
As a result, the effect of lime or eggshells also unfolds relatively slowly but steadily. By fertilizing with eggshells, one achieves a long-term effect, so to speak.
For which soil can eggshells be used as fertilizer?
Classic carbonic lime (i.e. calcium carbonate, which is the main component of eggshells) is effective only on loose, sandy or slightly clayey soils.
Eggshells as a fertilizer, however, work on heavy, clay-rich or heavily loamy soils because they are too chemically stable and cannot be affected by such a small amount of lime.
If you still want to fertilize clay-rich soils with lime and improve the pH value or the cementation, you should rather use quicklime.
Quicklime is nothing more than wood ash, preferably from organic and untreated wood. You can read more about what to look for when using ash as fertilizer here.
How do I fertilize with eggshells?
If you want to know how to make fertilizer from eggshells, it’s best to check out this article. There you will find a simple step-by-step guide to making eggshell fertilizer.
In the instructions you will read that it is best to make an eggshell solution and then water your plants with it.
The eggshells should be very much crushed and added to the water to dissolve.
Nevertheless, after a few days in the water even very small parts will not be dissolved for a long time.
Therefore, when watering with the eggshell solution, you should make sure that you do not water on the leaves or fruits of the plants, but directly into the soil towards the root system.
Otherwise, the plants can get unsightly white lime spots or the fertilizer does not reach directly where it works best – namely the roots through which the plants absorb their nutrients.
How often and how much should I fertilize with eggshells?
Here there is a clear rule of thumb that assumes a light rather sandy soil: then you can use without problems per year about 30-50 grams of eggshells per square meter.
One eggshell weighs about 10 grams, which means 3-5 eggshells per square meter annually.
In the instructions for making eggshell fertilizer (which you can find here) you will read that you should dissolve about 2-3 eggshells in a liter of water. So at 3-5 eggshells per square meter per year, that would be about 2 liters of eggshell solution per square meter that you can apply per year.
In order to provide the plants with an ideal supply of nutrients, I recommend that you apply this amount during the spring or summer.
So either you regularly pour small amounts of eggshell fertilizer on your flowers or the bed or, for example, twice a year a little more.
Which plants eggshells are suitable as fertilizer
As already mentioned, the lime in eggshells neutralizes the soil or brings it into the alkaline or basic range (pH >7).
Thus, fertilizer made from eggshells is especially suitable for plants that like alkaline soils.
Eggshells as fertilizer for roses
Roses need a slightly acidic soil with a pH of about 5.5-6.5, which is why eggshells are unsuitable as a fertilizer for roses.
If you are looking for an organic, homemade fertilizer for roses, then you should much rather switch to coffee grounds (as described in more detail in this article) or even banana peels (as described in more detail here).
Eggshells for cucumbers
Since cucumbers prefer a neutral to slightly acidic soil, with a pH of about 5.5-7.0, eggshells are not ideal for fertilizing cucumbers.
The lime content in eggshells raises or neutralizes the pH of the soil. Small amounts of eggshells should not harm cucumbers, but fertilizing cucumbers with larger amounts of eggshells or eggshell broth should be refrained from.
Eggshells as fertilizer for tomatoes
Eggshells make a good fertilizer for tomatoes because although they require a minimally acidic to neutral soil, they are not very sensitive to pH.
On the contrary, tomatoes are heavy feeders and thus need a large amount of nutrients, which are also present in eggshells, among other things.
Tomatoes can therefore be fertilized with eggshells from time to time without any problems.
Eggshells as fertilizer for herbs
Eggshells are suitable as fertilizer for herbs that prefer a neutral to alkaline soil. The best known herbs that like lime and therefore eggshells are bear and angelica, parsley, peppermint or quender.
Eggshells for hydrangeas
Eggshells should not be used to fertilize hydrangeas.
This is because hydrangeas are known to need a fairly acidic soil pH (between 4.0 and 6.0). However, eggshells would neutralize or increase the pH and worsen or even destroy the growing conditions for hydrangeas.
A much better, natural and homemade fertilizer for hydrangeas is coffee grounds, which are naturally acidic. Check here if you want to know how to make fertilizer from coffee grounds.