Myth or Fact: Can You Turn Hydrangeas Blue With a Rusty Nail?

Using rusty nails in your garden to get blue hydrangea flowers is a common gardening tale you may have seen floating around the internet. However, science does not necessarily back these claims. Gardening expert Jill Drago discusses whether rusty nails will help to turn your hydrangea blossoms blue.

Close-up of a gardener's gloved hand holding a rusty nail next to blooming blue hydrangeas in a sunny garden.

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Hydrangea blossoms are beautiful and range widely in size, shape, and color. The blue flowers of the bigleaf hydrangea are coveted for their dreamlike appearance. They are billowy and add an uncommon color to your gardens. They age beautifully and make for great dried flowers.

Just like us, plants need specific nutrients to grow healthy and strong. It is these nutrients that help plants develop chlorophyll, which leads to their lush green leaves. Nutrients are also responsible for the quantity of your plant’s blooms and, in this case, what color they will be. 

This article will discuss this myth and whether or not adding nails to the soil will help turn your hydrangeas blue

The Short Answer

While this gardening hack seems simple and requires minimal supplies, adding rusty nails to the soil surrounding your hydrangeas will not turn your hydrangea blossoms blue. The “rust” that accumulates on old nails is iron oxide. Iron oxide is an insoluble form of iron that will not make any difference in soil pH.

The Long Answer

While many gardeners have claimed that rusty nails have magically turned their hydrangea blossoms blue, there has to be more to their stories.

While they may have added rusty nails into their soil, we don’t know what else was going on in their soil at the same time. This makes it difficult to prove that the rusty nail helped their hydrangea blossoms to turn blue.

Do Rusty Nails Change Hydrangea Color?

Close-up of blooming Hydrangea macrophylla against a blurred green background. The plant produces large showy, globe-like flower heads in pink and blue. The distinctive mophead blooms consist of numerous individual flowers clustered together. The plant's large, coarse leaves provide an attractive backdrop.
Rusty nails, despite containing iron, won’t impact soil pH or hydrangea flower color.

No, they do not. Rusty nails may contain iron, which is useful in producing chlorophyll but has nothing to do with altering the pH of the soil and, hence, increasing the uptake of aluminum by hydrangeas needed for blue flowers.

Iron is found naturally in most soils and does not commonly need to be added for the health of your plants. However, because the iron oxide found in rusty nails is virtually insoluble, it will not have any impact on soil nutrient levels, let alone alter the pH. It does nothing to change your hydrangea flowers to the dreamy shade of blue we all hope for. 

The Role of Aluminum (not iron) in Changing Hydrangea Color

Close-up of flowering hydrangea bushes in the garden. Hydrangea macrophylla features large, serrated leaves and striking globe-shaped flower clusters. The leaves are broad and toothed, providing a lush, green backdrop to the garden. The plant has showy flowers, which form dense, ball-like clusters called mopheads. The flower heads are composed of smaller, individual flowers of a delicate blue color with a pinkish center.
Hydrangea flower color depends on soil pH, which affects aluminum uptake.

Changing the color of your hydrangea blossoms is often associated with your soil’s pH. This is true, but it is not the only factor. According to the University of Georgia, hydrangea blossoms turn blue due to the uptake of aluminum. If the pH is too sweet or alkaline, your hydrangea will not be able to take up enough aluminum to produce blue flowers. 

Messing with soil pH can be tricky business. Before you attempt any type of amending, you should begin with a soil test. These tests will tell you the pH as well as any nutrient deficiencies. 

If you learn that you need to lower the pH, there are steps you can take. It will take a few seasons, some patience from you, and accurate applications, but if you can stick to the plan, you will see results. 

Are There Any Benefits of Adding Rusty Nails to the Soil?

Close-up of Rusty nails on the ground. Rusty nails exhibit a weathered appearance characterized by a reddish-brown or orange coating of iron oxide. Nails are slender, pointed metal fasteners with a typically cylindrical shaft.
Rusty nails won’t supply sufficient iron for plants.

The long and short of it is no. While iron is a nutrient that plants need, adding rusty nails won’t provide enough iron to make a difference. If the soil lacks iron, supplement it with a liquid iron amendment. Alternatively, opt for a gentler approach and apply a fertilizer with added iron, such as iron-tone. 

A lack of iron in the soil can cause chlorosis. A sign of chlorosis in your plants is yellowing leaves. This would be a good reason to treat your affected plants with an iron-heavy fertilizer.

What is the Final Verdict?

Close-up of a pile of rusty used nails on the ground. Nails appear as slender, elongated metal fasteners with a pointed end and a flat, broader head. They are covered with a rusty brown-orange coating and have a rough texture.
Avoid placing rusty nails in the soil as it offers no plant benefits and poses a tetanus risk to humans and animals.

Do not do this. Not only is there no benefit for your plants, but you could injure yourself or an unknowing animal. Injuring yourself on a rusty nail or any metal can potentially cause tetanus if you are not vaccinated. Rusty nails in the ground will only increase the chances of this with no positive impact, so why bother?

How Can I Turn My Hydrangea Blossoms Blue?

Close-up of a woman's hand touching a blooming hydrangea flower on a blurred green background. The bigleaf blue hydrangea is characterized by its large, mophead-like clusters of vibrant blue flowers. The distinctive blooms are composed of numerous small, individual flowers packed closely together. The serrated, ovate leaves of the bigleaf hydrangea are dark green and sizable.
Determine your hydrangea’s sensitivity first and test your soil pH before attempting any alterations.

Before you do anything to your soil, there are two necessary steps to take for that desirable blue hue.

The first is ensuring that the type of hydrangea you are growing is sensitive to acidity. Hydrangea macrophylla, or bigleaf hydrangea, as well as Hydrangea serrata, or mountain hydrangea, are the only hydrangea species sensitive enough to alter the color of their blossoms. But wait, there’s more! The variety of hydrangea needs to be pink, blue, or purple. White hydrangeas will not react to change their color. 

The second is you must find out the pH of your soil. Adding anything with the hopes of altering the appearance of your plant is a gardening task that should not be taken lightly. Once you know your pH, you can decide how to work with it. You may be surprised and not need to do anything at all. 

If you need to acidify, you will need to do so by using a soil acidifier. These are easily found at your local garden centers or hardware stores. Soil acidifiers should contain sulfur, which will safely lower the pH. 

Depending on which product you select, I love the soil acidifier by Espoma. Follow the application instructions on the package. Soil acidifiers should be applied in spring and again every 60 days. Continue to test the pH until you have reached your desired levels. This should be 5.5 or lower. 

Bluing your hydrangeas can take time, but getting your pH to the correct level is the best way to aid your hydrangeas in absorbing aluminum, resulting in the blue blossoms of your dreams. 

Final Thoughts

Unfortunately, this is another gardening myth. I do not doubt gardeners’ tales of their luck with this method. However, none of these experiments were done in a controlled and well-documented situation.

The bottom line is that while iron is beneficial and very important for the overall function of the plant, it has nothing to do with the soil pH or the assistance in the uptake of surrounding nutrients. Stick to the tried and true methods, and you will be very happy with your results. 

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