Leslie Massey
Hydrangeas are cherished for their stunning blooms, which can range from blue to pink and even purple. The colour of hydrangeas depends on the pH level of the soil they grow in. Blue hydrangeas grow in acidic soils, usually with a pH of 5.5 or less, while pink hydrangeas grow in alkaline soils with a pH of 6 or more. To turn your hydrangeas blue, you can add aluminium sulfate, apple cider vinegar, coffee grounds, or rusty nails to the soil to increase its acidity. However, it's important to be patient, as the transformation is gradual and can take a few weeks to a couple of months. With some time and care, you can enjoy the beautiful blue hues of hydrangeas in your Australian garden.
| Characteristics | Values |
|---|---|
| Soil pH | Below 5.5 to 6.5 |
| Soil Type | Acidic |
| Aluminium | Required |
| Apple Cider Vinegar | Can be used to lower soil pH |
| Coffee Grounds | Can be used to make the soil more acidic |
| Soil Acidifier | Can be used to boost soil acidity |
| Aluminium Sulfate | Can be used to make the soil more acidic |
| Fertiliser | High-phosphorus fertiliser can be used to turn hydrangeas pink |
| Limestone | Can be added to the soil to turn hydrangeas pink |
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What You'll Learn
Use acidic soil with a pH below 5.5
To achieve blue hydrangeas, the soil must be acidic, with a pH level below 5.5. The colour blue in hydrangeas is influenced by the availability of aluminium ions in the soil. In acidic conditions, aluminium ions are more readily absorbed by the plant roots, resulting in blue flowers.
To acidify your soil, you can use aluminium sulfate, which can be found at most garden centres. Mix 1/4 oz of aluminium sulfate with a gallon of water and soak the soil surrounding your hydrangeas in the spring, as soon as the plant begins to grow. You can also use apple cider vinegar to lower the soil's pH. Mix one cup of apple cider vinegar with 10 litres of water and apply the solution directly to the base of the hydrangea, avoiding the leaves. Do this every couple of weeks, and the colour will gradually change.
Coffee grounds can also help make the soil more acidic. When added to the soil, coffee grounds release nitrogen and may slightly lower the pH, promoting blue coloration. You can also combine coffee grounds with fertiliser and citrus peels to further enhance the soil's acidity.
It is important to note that not all hydrangea varieties will react the same way to soil amendments. Additionally, changing the colour of hydrangeas mid-season is challenging, as soil changes affect developing buds. For a colour shift, start adjusting the soil's pH before your hydrangea sets its buds.
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Add aluminium sulfate or a soil acidifier
Blue hydrangeas require acidic soil, usually with a pH of 5.5 or less. Aluminium sulfate is a proven method for changing flower colour. It can be found at most garden centres. To use it, mix 1/4 oz of aluminium sulfate with a gallon of water and soak the soil surrounding your hydrangeas in the spring, as soon as the plant begins to grow. You may need to apply it multiple times to make your soil acidic enough for blue hydrangeas. Re-test your soil's pH and adjust your treatments as necessary.
If your hydrangeas have already bloomed pink, you will have to wait until next year to see blue flowers. It is important to remember that flower colour won't change overnight. It is a slow process that takes time and patience.
There are other methods to acidify your soil, such as adding coffee grounds, vinegar, rusty nails, or pennies to the soil. However, these methods may be less effective than using aluminium sulfate. For example, apple cider vinegar should be used carefully to avoid excessive acidity that could harm the plant.
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Avoid eggshells and other alkaline products
To grow blue hydrangeas, it is essential to maintain acidic soil with a pH level below 6.5. Eggshells, primarily composed of calcium carbonate, can increase the soil's pH, making it more alkaline. Therefore, eggshells should be avoided to prevent pink blooms instead of blue.
Eggshells are not the only product to avoid when trying to grow blue hydrangeas. Any alkaline products should be avoided, as they will increase the pH level of the soil. For example, limestone is an alkaline product that can be added to the soil to encourage pink blooms. Similarly, lime products can be used to increase alkalinity and achieve pink hydrangeas.
In addition to eggshells and lime products, gardeners should avoid using aluminium-based products or acidic fertilizers if they want to grow blue hydrangeas. This is because the colour of hydrangeas is influenced by the availability of aluminium ions in the soil. In acidic conditions, aluminium ions are more readily absorbed by the plant roots, resulting in blue flowers. Therefore, gardeners should avoid any products that could reduce the absorption of aluminium ions.
To test the pH level of the soil, gardeners can purchase cheap pH testing kits from garden centres or online. By regularly testing the soil pH, gardeners can ensure that their soil remains acidic enough to grow blue hydrangeas.
Overall, to successfully grow blue hydrangeas, it is crucial to avoid eggshells and other alkaline products that can increase the pH level of the soil. By maintaining acidic soil with a pH below 6.5, gardeners can achieve the desired blue blooms.
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Apple cider vinegar can help turn hydrangeas blue
To apply apple cider vinegar to your hydrangeas, mix one cup of it with 10 litres of water (an average watering can's worth). Direct the solution at the base of the hydrangea, avoiding the leaves. Do this every couple of weeks, and the colour will gradually change. You can control the 'bluing' by reducing or discarding the vinegar once the desired hue is achieved.
It is important to note that vinegar can damage the leaves of your hydrangea, so ensure that the mixture is diluted enough and only hits the roots of the plant. Over time, too much vinegar may damage your garden. Therefore, it is recommended to start with a low rate and increase the amount if you notice success.
Additionally, eggshells should be avoided when aiming for blue flowers. Eggshells are primarily made of calcium carbonate, which can raise soil pH and make it more alkaline, resulting in pink blooms.
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Coffee grounds can make the soil more acidic
The colour of hydrangeas is influenced by the pH level of the soil they grow in. Blue hydrangeas grow in acidic soil, usually with a pH of 5.5 or less. To achieve this, gardeners often use aluminium sulphate, which can be found at most garden centres. However, some sources suggest that coffee grounds can also be used to make the soil more acidic.
Coffee grounds have a pH of around 6.2, which is slightly acidic. When added to the soil, they release nitrogen and may slightly lower the pH, promoting blue hydrangea growth. However, the effect of coffee grounds on soil acidity is debated. Some gardeners claim that coffee grounds do not affect the pH of the soil, while others assert that they can lower it slightly. The science is not entirely clear on this matter.
To effectively use coffee grounds to increase soil acidity, the volume of coffee grounds must be considered in relation to the quantity of soil. A significant amount of coffee grounds may be required to noticeably affect the pH of the soil. Additionally, the type of coffee bean and brewing method can impact the acidity of coffee grounds.
It is worth noting that coffee grounds have other benefits for soil beyond potentially increasing acidity. They can improve soil structure, drainage, and nutrient content. However, they should be used in moderation, as excessive amounts may be detrimental. When used appropriately, coffee grounds can be a useful tool for gardeners aiming to create the ideal conditions for blue hydrangeas.
In conclusion, while coffee grounds may not be the most efficient or reliable method for acidifying soil, they can be used as part of a larger strategy to create the optimal environment for blue hydrangeas. Gardeners can also employ other techniques, such as using apple cider vinegar or ericaceous compost, to achieve the desired soil acidity for vibrant blue hydrangeas.
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Frequently asked questions
To turn your hydrangeas blue, you need to create more acidic soil with a pH below 5.5. You can do this by adding aluminium sulfate or a soil acidifier to the base of the plant. You can also use vinegar, coffee grounds, rusty nails, or sulfur to make the soil more acidic.
Changing the colour of your hydrangeas is a gradual process that takes time and patience. It may require multiple applications of aluminium sulfate to make your soil acidic enough, and you may not see blue flowers until next year.
Not all hydrangeas change colour. It is primarily bigleaf (Hydrangea macrophylla) and mountain hydrangeas (Hydrangea serrata) that can shift from pink to blue based on soil pH. If your soil pH is too high, you can add vinegar, coffee grounds, or rusty nails to make it more acidic.
You can test the pH of your soil with a cheap pH testing kit available at any garden centre. The desired pH level for blue hydrangeas is 6.5 or lower, and aluminium must be present in the soil.
