pH is a scientific term that describes the amount, or “power” (hence the “p”), of hydrogen (the “H”) that’s available within the soil. The hydrogen ions are what enable a plant’s roots to absorb the various nutrients from the soil. The pH of soil ranges from 0 to 14, and we speak of low pH soil as being “acidic” and high pH soil as being “alkaline.” Generally speaking, areas with heavy rainfall and a lot of forests have acidic soil, and drier areas of desert terrain have alkaline soil. Plains with less rainfall and lighter cover tend to have neutral soils.
Some hydrangeas are very sensitive to the pH of the soil in which they are grown, and this sensitivity is reflected in the color of their blossoms. Most French hydrangeas (Hydrangea macrophylla) have, over the centuries, developed this sensitivity. In acidic soil (below a pH of 6), their flowers will be blue. In alkaline soil (with a pH above 7), their flowers will be pink, or even red. In neutral to slightly acid soil, these hydrangeas can have purple blooms, or even a mixture of pink and blue blooms on the same plant.
There are exceptions to every rule, of course, and there are some exceptions here. Hydrangeas with white blossoms will always bloom in white, no matter the pH of the soil. Some individual cultivars stick to their color in all but the most extreme conditions. For example, Ami Pasquier remains red unless the soil is extremely acidic, in which case, it turns purple, but never truly blue. Purple Tiers remains purple regardless of the pH of the soil.
Hydrangeas are a beloved garden flower known for their large, colorful blooms. One trick to growing gorgeous hydrangeas is understanding how soil pH affects the flower color. This often leads gardeners to ask – is lime good for hydrangeas?
Lime, or calcium carbonate, is an alkaline substance that raises pH. This impacts the availability of aluminum in the soil, which produces the blue pigment in hydrangea blossoms.
So what does this mean for using lime on hydrangeas? Below we’ll explore the key considerations including how lime impacts color whether it’s recommended, and safe application tips.
How Lime Impacts Hydrangea Bloom Color
The majority of hydrangea varieties change flower color based on the acidity or alkalinity of the soil. This is because aluminum availability impacts pigment production.
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Acidic soils below pH 60 induce blue blooms due to abundant soluble aluminum.
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Alkaline soils over pH 7.0 limit aluminum availability, resulting in pink or red flowers.
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The ideal pH range for growing hydrangeas is slightly acidic, between 5.2-6.2, which encourages beautiful blue/purple hues.
Lime is calcium carbonate, an alkaline substance. Adding lime raises the pH, making the soil more basic. Therefore, applying lime to acidic soils will turn hydrangea blooms pink or red.
Should You Use Lime on Hydrangeas?
Whether using lime on hydrangeas is recommended depends on your goals for bloom color.
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To maintain blue flowers, avoid using lime. Stick to acidic soil between pH 5.2-6.2 instead.
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If your soil already falls in the ideal pH range, there is no need to alter it with lime to change color.
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To purposely make flowers pink or red, mix lime into the soil around the roots. How much to add depends on your starting pH.
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Never add lime without testing your soil first, as too much can damage plants. It’s easier to raise pH than lower it.
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The effects of lime last for multiple seasons, so go cautiously. It can be difficult to reverse once applied.
How to Safely Use Lime on Hydrangeas
If your aim is pink or red blooms, here are some tips for using lime on hydrangeas safely:
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Always test current soil pH before adding lime or other amendments. Home kits are inexpensive.
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Use soil test results to determine how much lime is needed to raise the pH just slightly. More is not better.
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At planting, mix lime deeply into the hole. For established plants, sprinkle lightly around the root zone.
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Choose powdered dolomitic lime as it contains calcium and magnesium, both beneficial to hydrangeas.
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Recheck pH after 2-4 weeks to see if more lime is needed after the initial application.
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Lime just once or twice early in the growing season. Overapplying can burn plant roots and leaves.
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Consider acidic fertilizers with iron, sulfur, and aluminum instead if unsure about using lime.
Problems Caused by Excess Lime
While a small amount of lime nudges soil pH up gradually, overdoing it harms hydrangeas. Too much lime can lead to:
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Burnt leaf margins from highly alkaline soil burning the roots.
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Wilting and stunted growth as damaged roots fail to absorb moisture.
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Nutrient deficiencies as minerals lock up and become unavailable in overly alkaline soil.
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Few or no flowers since the stressed plant focuses energy on survival rather than blooming.
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Potential death if the soil nutrient balance is completely disrupted and not corrected quickly.
The impact depends on the excess amount applied and how soon remedial action is taken. Lightly working sulfur into the soil can help lower pH if caught early enough.
Achieving Blue Hydrangea Flowers Without Lime
Luckily there are several ways to coax blue blooms without using lime:
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Select naturally acidic planting sites, like under pine trees. Avoid recent lime applications.
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Incorporate acidic peat moss or compost into the soil. Coffee grounds also help lower pH.
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Use an acidic fertilizer formulated for hydrangeas. Options contain iron, sulfur, and aluminum to blue flowers.
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Try aluminum sulfate fertilizer, which is very effective at turning hydrangeas blue.
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Grow hydrangea varieties bred to bloom blue regardless of soil pH. Many panicle and smooth types have this trait.
Should you put lime on hydrangeas? Carefully applied, it can gently raise soil pH to pink up flowers. But lime is unnecessary if your goal is blue blooms, which most hydrangea fans desire.
Focus on keeping soil slightly acidic by choosing the right planting site, using acidic amendments, and selecting certain varieties. With a little planning, you can enjoy vivid blue hydrangea blossoms summer after summer without ever using lime.
Other Factors that Impact Hydrangea Blossoms
Other elements can affect hydrangea blossoms. For example, some say that hot weather will prevent any hydrangea from turning a true crimson or red, no matter how alkaline the soil may be. The depth and intensity of the blossom color is impacted by factors that you will have less control over, such as the weather conditions, the amount of humidity, and the health of the plant. It is also possible that the amount of aluminum in the soil has as much effect as acidic soil on the tendency for hydrangeas to bloom in blue.
Changing the pH of Your Soil
If you do want to control the color range of your hydrangea blossoms, changing the pH of your soil is the most straightforward method.
Limelight Hydrangeas // 1 Year Update // Garden Answer
FAQ
When should I add lime to hydrangeas?
Adding lime to raise the pH would change the color. You should add the lime in August or September, to allow time to bind the aluminum so it won’t be taken up by the plant in early spring. Since your native soils are acidic, as you mentioned, they will continually buffer the lime to stabilize the pH.
What is the best fertilizer for hydrangeas?
The best fertilizer for hydrangeas is a balanced, slow-release fertilizer with an NPK ratio of 10-10-10 or similar. Specialty fertilizers formulated for flowering shrubs or specifically for hydrangeas often include micronutrients that promote healthy growth and blooming.
What does garden lime do for hydrangeas?
Garden Lime will raise the pH of your soil to increase the red and pink colors in your macrophylla big-leaf hydrangeas.
What do you put on hydrangeas to turn them blue?
To turn hydrangeas blue, you need to increase the acidity of the soil. This is because blue hydrangeas thrive in acidic soil with a pH of 5.5 or lower, according to Garden Design. Adding aluminum sulfate or wettable sulfur are effective ways to lower the soil pH.
Should you add lime to hydrangeas?
Adding lime raises the pH, making the soil more basic. Therefore, applying lime to hydrangeas in acidic soil will make the blooms turn pink or red. The typical recommended soil pH range for growing hydrangeas is slightly acidic, between 5.2 and 6.2. This encourages beautiful, vivid blue or purple blooms. Should You Add Lime to Your Hydrangeas?
How much lime do hydrangeas need?
Hydrangeas grow best in soil with a pH between 5.0 and 5.5. Before adding lime, have a soil test done to determine the pH level. The soil test will also tell you how much lime you need to add in order to reach a pH of 5.5. Generally, you should add about 5 lbs per 100 sq ft of garden area if the soil test indicates a pH above 7.0.
Does lime affect Hydrangea flower color?
Applying lime to hydrangeas will not affect the flower color directly; however, the way lime affects the soil composition can result in the desired effects of the desired shade of pink or purple blooms. Lime works to increase the acidity levels of the soil, which results in a change in the pH value from alkaline sandy to acidic clay.
Does lime make hydrangeas blue?
Lime Does not Make Hydrangeas Blue. Using Lime (CaCO3) on Hydrangea would make the blooms turn pink. To turn the blooms to blue, you need to use another chemical compound Aluminum Sulphate (Al 2 (SO 4) 3) in the soil. Should I put lime on my Hydrangea? Adding Lime to Hydrangeas is not a requirement for Hydrangea.
Can hydrangeas grow in acidic soil?
Lime, or calcium carbonate, is an alkaline substance. Adding lime raises the pH, making the soil more basic. Therefore, applying lime to hydrangeas in acidic soil will make the blooms turn pink or red. The typical recommended soil pH range for growing hydrangeas is slightly acidic, between 5.2 and 6.2.
What happens if you add too much lime to hydrangeas?
While a little lime can gently nudge blooms to pink, overdoing it has consequences. Adding too much lime to hydrangeas can result in: The impact depends on how much excess lime was applied and how quickly you can try to remedy the situation. Lightly sprinkling in some sulfur can help lower pH if caught soon enough.