Are Eggshells Good or Bad For Hydrangeas?

Thinking of using eggshells with your hydrangeas this season? Many gardeners swear by eggshells as a fertilizer component, but will they have a positive or negative impact on your beautiful hydrangeas? In this article, gardening expert Jill Drago examines this common garden practice and if it's one you should avoid this season.

eggshells hydrangeas

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Gardening can be an expensive hobby. Between the plants, fertilizer, mulch, and tools, the cost can rack up quite quickly. I know I am always searching for new ways to beautify my garden at a low cost.

Sometimes this is dividing my plants instead of buying new ones, or planting flower or vegetable seeds instead of purchasing already grown seedlings.

Adding eggshells to your garden is an exciting concept. If you eat a lot of eggs for breakfast, then you likely have a ton of eggshells that are ending up in your trash can or, hopefully, your compost bin.

What is the scoop with eggshells and hydrangeas? Is it beneficial to add this kitchen scrap to your hydrangea gardens, or is it just another hydrangea myth? Let’s dig in and find out a bit more about this gardening hack.

The Short Answer

Eggshells are a wonderful way to add slow-release calcium to your garden, whether you are adding them directly to your garden soil or to your compost bin. However, when it comes to using eggshells around your hydrangeas it gets a little tricky. At the end of the day, I do not believe that eggshells will significantly harm your hydrangeas. In fact, the addition of eggshells into your hydrangea gardens may offer health benefits over time.

The Long Answer

Close-up of a woman holding a wooden bowl full of brown and white eggshells, against a blurred garden background. The woman is wearing gray gloves and a gray apron.
Eggshells have calcium which is essential for plant growth but takes a year to decompose and leach into the soil.

The greatest gardening benefit the eggshell has to offer is its amount of calcium. Unfortunately, this calcium is not immediately available to your gardens. You will need about a year of decomposing before the calcium breaks down enough to permeate into your soil.

The calcium found in eggshells is calcium carbonate. This is one of many micronutrients essential for cellular formation in plants.

Calcium carbonate is a main component of limestone, which is widely known for increasing the pH of your soil to a more alkaline level. Soil pH below 6.0 will turn your hydrangea blossoms blue, and the presence of acidic materials such as sulfur or aluminum sulfate can lower the soil pH. Above 7.0, alkalinity causes hydrangeas to skew towards the pink range, and calcium or limestone will turn the flowers pink.

Eggshells and Hydrangeas

Top view, close-up of a young hydrangea plant in the garden with scattered crushed eggshells on the soil. The plant has large oval green leaves with serrated edges.
Before adding eggshells to your hydrangea garden, consider the potential effect on soil pH and the color of bigleaf hydrangea flowers.

If you are thinking about adding eggshells to your hydrangea garden, it is important to know why you want to do so and what you expect the results to be.

The calcium loaded into these eggshells can interfere with the pH of your garden soil. This is not detrimental to the overall health of your hydrangea, but it could alter the pH enough to change the color of your bigleaf hydrangea flowers.

Further, calcium carbonate does not decay in the soil the way that other additives do; it can remain present in the soil for many years. With each addition of calcium, you can gradually be increasing your soil pH over time — and if you want blue flowers or those lovely purple-tinged intermediary blooms, you’ll need to stay with a lower pH level.

Changing Flower Colors

Close-up of a large flowering hydrangea bush in the garden. Hydrangea flowers are large and showy, with clusters of small four-petalled flowers in round inflorescences. Flowers are pale pink and pale blue.
Eggshells can change bigleaf hydrangea flower color, but it takes some time.

In theory, eggshells will eventually change the color of your bigleaf hydrangea flowers. It will take some time for the eggshells to break down properly and actually affect the pH of your soil. All in all, I think there are better ways to change your flowers from blue to pink.

Garden lime, which is made of calcium carbonate just like egg shells, will work much quicker at raising the pH of your soil. Once you have garden lime on hand, it is important to follow package instructions to ensure that you are using the correct application rate.

If this is overwhelming, I would look for a garden lime product marketed specifically for hydrangeas and changing your soil’s pH.

Calcium Deficiency

Close-up of a man's hand showing hydrangea leaves in the garden. The leaves are large, oval-shaped, with serrated edges, yellowish due to a lack of nutrients, including calcium and phosphorus.
Calcium deficiency signs include smaller and lighter-colored leaves with distortion.

Yes, the eggshells are loaded with calcium which can be an excellent fertilizer. Even though most soils do not need extra calcium, it’s easy to find out by having a professional soil test done and learning all about your soil.

If you think your plants may be suffering from a calcium deficiency, there are a few things you can look out for. When hydrangea leaves are uncurling, you may notice that they are smaller in size and much lighter in color. It may appear that you can see through the leaves as they seem a bit translucent (although many other things can cause that, too). Lastly, the leaves may be distorted in size.

How to Apply

A close-up of a gardener's hand in a white glove pouring crushed eggshells into the black soil in a garden as fertilizer.
You can apply eggshells to your garden by crushing them and scattering around plants or making eggshell water.

You can apply eggshells to your garden in two different ways. The most effective way is to crush your eggshells into powder and scatter the dust around your plants or in the holes you dig for your plants. While the powdered eggshell will still take a long time to break down, it will eventually become plant available.

Another way popularized online is making eggshell water. This is not as simple as just soaking eggshells in water, however. To break down the calcium into a form that is absorbable by plants, you’ll need to add an acid, such as white vinegar.

A very basic recipe is to blend 5 teaspoons of powdered eggshells to 5 teaspoons of household-grade white vinegar in a large bowl, and stir it well to combine. This will foam up considerably and you’ll want it to sit for a while as the acid reacts with the base. Have a gallon of water at the ready. After 30 minutes, start adding water to the bowl and stirring until you have an easily-pourable slurry, then add all of that back into the rest of your gallon of water. Use this mixture in the garden within 24-48 hours for the best effect.

The problem with tricks like this is that there is not a lot of good information on application rates, meaning we don’t really know how much is too much or how much is safe to use on your hydrangeas. In many cases, it’s best to save your eggshell water or crushed eggshells for plants that you know will use the calcium, such as tomatoes!

Other Egg Shell Uses

There are plenty of other ways you can use eggshells safely as part of your gardening routine, even with hydrangeas. Let’s take a deeper look at some of the most common uses.

Compost

Egg shells on a compost heap close-up. Food and organic waste lie in a compost bin for decomposition.
Add crushed eggshells to compost after rinsing and drying them to eliminate odor and speed up decomposition.

Adding eggshells to your compost is a great way to lighten some of your kitchen trash load. Be sure to rinse and dry your shells before adding them to the pile; this will help eliminate any odor that may attract animals.

For the best results, powder the shells. This will help them break down a bit quicker than if you left them in larger pieces.

Fertilize Your Veggies

Close-up of crushed eggshells scattered on the ground as organic fertilizer for vegetable sprouts. The sprouts have thin, pale green stems and round, slightly heart-shaped, pale green leaves.
Crushed or powdered eggshells can boost vegetable growth by providing calcium.

The calcium in the eggshells can be beneficial to some types of vegetables, such as tomatoes, squash, or eggplant. However, there are limitations here, as well.

It’s best to add a small amount of powdered eggshell to your future tomato bed in the fall and let it start to break down over the winter and early spring. That way, by the time you start getting fruit, some of the calcium may be plant-available and can reduce the occurrence of blossom end rot.

Be careful, however — in this situation, more is not better! Too alkaline of a pH level can actually lock up the calcium in the soil and prevent nutrient uptake. In addition, most blossom end rot is caused by uneven watering, as the plant requires moisture to absorb the calcium.

Worm Composting

Composted worms crawling around in garden dirt. The red worms are making the soil more fertile.
Worms like powdered eggshells and can improve soil health.

Did you know that worms use powdered eggshells to digest their food?

Since a worm doesn’t have teeth, it has to digest its food somehow. And to do it, the worm uses grit. It eats the grit along with its food, and when everything reaches the worm’s gizzard, the grit helps to break down the food it’s consumed and helps the worm convert its future waste into the lovely worm poop we call worm castings or vermicompost.

Eggshells, if powdered finely, make a lovely grit for worms! Any excess grit will be passed through the worm and out into their castings, so you’ll end up with the benefit of the calcium in your soil along with the added benefits of vermicompost.

Insect Deterrent

Close-up of a small snail on an eggshell, on a pink background. The snail has a soft, slimy body and a helical spiral shell on its back.
Crushed eggshells can physically damage soft-bodied insects like slugs and snails.

Crushing up your eggshells may keep some insects away from your gardens. The sharp edges of the shells can physically damage insects such as slugs, snails, or other insects with soft bodies. However, this is a minor deterrent and often will not stop them from reaching your plants for long.

Final Thoughts

I love the idea of adding kitchen scraps to your garden. It seems to make a lot of sense, and it also seems like it should save you money. When it comes to hydrangeas, however, I just don’t see the point of adding the eggshells. You could end up with pink hydrangea blossoms when you are dreaming of blue. Crush those eggshells and add them to your worm bin instead.

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