Which Plants Do Not Like Eggshells?

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Gardeners have long used eggshells as another way of helping their plants to grow effectively. As with many long-held tips like using eggshells on plant beds, it can be hard to know what difference it makes and which plants do not benefit from eggshells.

Plants that are already in an ideal pH soil or calcium-rich environments may be negatively impacted by eggshells being added to the soil. Eggshells add calcium carbonate, which can change the qualities of the soil and impact growth.

It’s not always obvious which plants will and will not benefit from eggshells adding calcium to the soil. Keep reading to learn more about whether eggshells are suitable for your garden.

Why Do Some Plants Not Like Eggshells?

Eggshells can be a valuable addition to many gardens. Eggshells are mainly composed of calcium carbonate crystals (with small amounts of potassium, phosphorus, and magnesium), which will readily leech into their environment, especially when exposed to acidic matter.

The pH of calcium carbonate is around nine, meaning that it is more alkaline, and so when eggshells are added to the soil around plants, it can offset any acidity in the soil by neutralizing the acidity.

There are two main reasons plants can be negatively affected by eggshells being added to the soil. These are:

The plant prefers a more acidic environment
The plant already has more than enough calcium available

Plants Preferring an Acidic Environment

The growth of plants will depend on many different factors, and one of the most important is the acidity (or alkalinity) of the soil in which they are planted. This is generally a result of the evolutionary process that the plant has been through and the areas to which it is native. These are the conditions that it evolved through, and so will typically be genetically hardwired to prefer.

The acidity or alkalinity of the soil in which plants live is measured using the standard scale, called pH, which is a numerical range from 0–14. A pH of seven represents a neutral state, with lower numbers increasingly acidic and numbers higher than seven increasingly alkaline (or basic).

pH 1 – Strong Acid

pH 7 – Neutral
pH 14 – Strong Base

Most plants usually prefer somewhere in the range of 6.5–7.5.

When we say that the plants’ prefer’ it, what we really mean is that the state of the soil will be more appropriate for facilitating the type of chemical processes which occur as the plant grows — and the acidity or alkalinity of the soil is considered to be a master variable in determining plant nutrient availability.

This goes to show that many plants will desire a pH of lower than seven, which is to say, acidic soil. Some examples of these are:

Rhododendrons

Azaleas
Heathers
Ferns

Magnolia
Hydrangeas

For these plants, if the soil they are in is only just acidic enough for them, introducing eggshells may mean that the soil can no longer adequately facilitate the chemical process that allows the plant to take on the nutrients it needs.

The Plant Already Has More Than Enough Calcium Available

All plants need calcium to grow effectively. In fact, not having enough calcium available to plants can cause a range of issues, the most well-known being blossom end rot. However, if there is already an abundance of calcium in the soil, adding eggshells may reduce the soil’s overall quality, which the plant relies on to grow effectively.

This video has more information on that.

https://youtu.be/8l7ScIh107o

While absorbing so much calcium as to be considered to be afflicted explicitly with calcium toxicity is almost unheard of, very high levels of calcium in the soil can have a knock-on effect.

Calcium typically exists as a cation in the soil, meaning that it holds a positive charge. Due to the way in which plants absorb nutrients, this can mean that high levels of calcium can impact the absorption of other positively charged substances in the soil. Other essential positively charged elements for plants are:

Magnesium

Potassium
Sodium

High levels of calcium can therefore induce a deficiency in these other elements and compounds, which can cause a raft of potential issues.

As a result, it’s imperative to consider the current condition of your soil with regard to both pH and nutrient balance before looking to add eggshells.

How Do I Know The pH Of My Soil?

It’s hard to say for sure whether your plants will benefit or otherwise from using eggshells in the soil without knowing its pH. The inevitable follow-up question is: how do I tell?

This is so often need-to-know information for gardeners that you can buy pre-packaged soil acidity tests, and as a result, there are two ways that we will cover:

How to determine soil pH with a test kit
How to determine soil pH without a test kit

With a Test Kit

If you have a kit already to hand, then it’s a very straightforward process to follow. Typically the kits will come with ‘test strips,’ which are usually made from a material called litmus paper. Litmus paper will change color based on the pH level of the solution it comes into contact with.

So in order to determine the pH level of our soil, we should take the following steps:

Take a small sample of soil
Add distilled water to make a soil solution

Dip the test strip into the soil and wait for 30 seconds

After these steps have been followed, you will typically see the test strip change color. If the strip is red, it indicates that the soil solution is acidic. If the strip is blue, it means that the soil solution is alkaline.

Sometimes, you may also notice that there is not a significant change in the color of the test strip. This is because if the pH of the soil solution is close to 7 — that is, of a neutral pH level — then the strip will remain unchanged.

If in doubt, you should consult the instructions that came with your test kit.

Without a Test Kit

If you don’t have a test kit, the process is a little trickier, but certainly still possible. You’ll need some white vinegar (which is an acid) and some backing soda (an alkali).

This time we’ll need to go through two tests, one to test for acidic soil and one to test for alkaline soil.

Testing For Acidic Soil

First, take one of the soil samples and add some distilled water to make a soil solution. Then, carefully add the baking soda and listen closely. We’re trying to identify whether a neutralization reaction is occurring, as this will mean that our alkaline baking soda is reacting with acidic soil.

We also care about the intensity of the reaction, as this will indicate to what degree the soil is acidic or basic. You can identify the reaction by an audible ‘fizzing’ noise. If you don’t think that there is a reaction at all, then the soil is probably not particularly acidic, and we move on to the next test.

Testing For Alkaline Soil

Now, take the second soil sample and again add some distilled water to create more soil solution. This time, we add the white vinegar and again listen for a reaction. If we identify one, then we know that the soil solution is alkaline because it has caused a neutralization reaction when mixed with an acid (white vinegar).

If there are no reactions, then you most likely have soil with a neutral pH.

How Do I Know If My Soil Has Too Much Calcium?

If your soil has too much calcium, then the most likely effect is a reduced ability for the plant to absorb other positively charged nutrients in the soil, such as:

Magnesium

Potassium
Sodium

As calcium toxicity is extremely rare, it means that the easiest way to identify whether the soil has too much calcium is by assessing whether the plants are deficient in the elements above.

Magnesium

Magnesium is used by plants to photosynthesize, so identification of magnesium deficiency is most straightforward by assessing the leaves of the plant. If you can see the leaves showing increased yellow discoloration between the veins and leaves falling off earlier than you would typically expect, this could well be a sign of magnesium deficiency.

Potassium

Potassium is used for water uptake across most plants but also plays a critical role in the production of fruit yields. A giveaway sign of potassium deficiency is yellow leaves which are brown at the edge of the leaf, alongside poor flower and fruit yields.

Sodium

Plants in soil that do not have appropriate sodium levels can see issues with water retention and will often become necrotic.

Soil pH

Soil that is heavy in calcium will also typically report a higher-than-expected soil pH, as the pH of calcium carbonate solution is around nine. This means that it is always worthwhile doing regular testing on soil pH in order to rule out other issues.

Do Eggshells Help Protect Plants from Slugs?

Slugs are a common pest in many gardens. They can have a serious impact if left to it, eating holes in many important plant parts, such as:

Leaves

Flowers
Stems
Tubers

Bulbs

They also are a year-round problem in many climates, so gardeners can be forgiven for looking for solutions to prevent the impact of slug damage.

One common piece of advice is to use eggshells to deter slugs. When used in the garden, eggshells are typically rolled into rough, jagged pieces with many sharp points. The idea is then that the slugs will be uncomfortable trying to pass over the jagged pieces and so head off elsewhere.

Unfortunately, research has shown that slugs are not deterred at all by eggshells in the garden. This should probably come as no surprise, given that some slugs have been shown to be able to travel over razor blades, meaning that eggshells are unlikely to present much of a challenge.

Can Eggshells Attract Rats or Ants?

Rats, ants, and other such visitors to the garden can cause serious issues, so it’s only natural that we try to avoid encouraging them in ourselves. One issue with introducing food matter to the garden is that it can have exactly this effect.

The shell of an egg, though, is not itself particularly appealing for rats, ants, or most other animals because it is mostly composed of calcium carbonate. However, the egg itself is incredibly appealing to animals who may visit the garden because it is an incredible source of dietary protein. This is part of the reason why so-called egg predation is so common in the wild across many different types of animals, such as:

Fish
Birds
Snakes

Mammals
Arthropods

This means that in order to reduce the chance of eggshell use attracting animals to the garden, it is important to carefully clean and rinse the eggshells prior to use. This should remove the vast majority of any lingering egg material.

How Should Eggshells Be Applied to Soil?

One of the key considerations in applying eggshells is the preparation work that should go on ahead of applying. Firstly, eggshells should always be completely cleaned of any remaining egg material from inside the shell. This will prevent issues with attracting other wildlife into the garden.

Eggshells should also be ground up into very small pieces, bordering on dust. This is because having the eggshells in a form that will allow for easier absorption into the soil will speed up the impact. Leaving large pieces of the shell will take a long time to break down, usually up to a year or more.

It’s also important that the eggshells be applied across a broad area in order to ensure that the impact on the soil — both in terms of calcium distribution and also the ultimate soil pH — is balanced across the whole area rather than applying to one small area.

Conclusion

It’s clear that while eggshells can be beneficial to many plants, it very much depends on the plants you have and the conditions that they are already in. Eggshells are a great tool to have as a gardener to be able to affect change in the soil to meet your plants’ needs — but you must first ensure it’s appropriate in the circumstances.

Sources

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