Hydrangeas come in a variety of colors, from white to green to deep crimson. One of the most popular varieties is the cheerful blue mophead bloom commonly found on Hydrangea shrubs. With variations in hue, these breathtaking beauties range from soft baby blue to deep violet and every color in between.
To make your Hydrangeas blue, you first need to test your soil to determine the pH level. For blue blooms, the soil needs to be acidic, with a pH level at or below 5.5. You can use simple additives to change the soil’s pH. To keep your Hydrangea blooms blue, simply monitor the pH and adjust it as needed.
It may feel like you’re back in your high school chemistry class, but don’t be intimidated by this process. It’s really easy (and fun!) to see your Hydrangea blooms change color until you get a shade of blue that’s just right for your lawn or garden.
What Makes Hydrangeas Blue?
For the most common Hydrangea varieties, the soil’s pH directly controls the expression of color. It’s just another little fact that makes these shrubs so desirable for your lawn or garden. There’s actually a lot going on underneath the soil to turn your Hydrangeas into your garden’s very own mood rings.
Garden Chemistry
Think of your Hydrangea bloom as a litmus paper, taking a sample of the soil below and changing color to indicate the acidity. Litmus paper turns red when dipped into an acidic solution, and it turns blue if it is dipped into a basic solution.
Like litmus paper (only with the colors reversed), Hydrangea blooms change color on a range, from a very light, soft pink to deep, vibrant blue, based on how acidic or alkaline the soil is.
However, the process isn’t just a simple result of the presence or absence of acidic materials. The color of your Hydrangea really depends on the amount of aluminum in the soil. Who knew that there was metal in your flowers?!
Don’t Let Your Plans for Blue Blooms Get… Foiled
Aluminum ions move through the Hydrangea’s root system and up into the plant much easier when the soil conditions are acidic. However, in soil that is more basic or neutral, the ions become immobilized. Blue Hydrangeas need both acidic soil and aluminum ions.
I won’t go into too much detail here because it gets pretty complicated, but if you want to learn more about the chemistry behind your Hydrangea’s color changes, check out this video from American Scientist.
Which Hydrangeas Can Be Blue?
The most common varieties, including the bigleaf Hydrangeas (Hydrangea macrophylla), have this chameleon-like ability to change colors. That means that if your flowers are pink, you can make them blue. Or, if they’re already blue, you can adjust the soil to make them lighter or darker or add a purple tint.
Common Blue Hydrangeas
Some of the most popular Hydrangeas that start blue, or can change to blue through soil manipulation, are some of the most widely available types out there. If you want a touch of this regal color in your garden, these varieties are a great place to start.
- Blushing Bride
- Nikko Blue
- Summer Lace
- Blue Wave
- Blue Heaven
- Nightingale
- Blue Deckle
- Pretty in Pink (Note: Don’t be fooled by the name. This little lovely has an equal chance of being blue or pink, depending on the soil’s pH level).
Hydrangeas that Don’t Change to Blue
Blooms that are creamy white are probably among the types that do not change color. These Hydrangeas are beautiful on their own but don’t waste your time or effort trying to turn them blue.Some of these single-color Hydrangeas include:
- Annabelle Hydrangeas
- Oakleaf Hydrangeas
- PeeGees (some varieties)
Are Hydrangeas Naturally Blue?
Some varieties of Hydrangea have naturally occurring blue hues in their blooms. But if planted in soil that is too alkaline, your Hydrangea will lose its blue color.
However, there are also plenty of Hydrangeas that are pink and naturally turn blue in certain soil conditions, or vice-versa. There is no Hydrangea that is permanently blue and does not respond to soil acidity the same way that some Hydrangeas are forever white.
How to Make Your Hydrangeas Turn Blue
Whether you’re just planting your Hydrangea, or if you have an established plant, you can do your own science experiment in your yard to change your Hydrangea’s color to blue. This can be done if your Hydrangea is pink or if you want to enhance the color to make it a more vibrant shade of blue.
To have blue Hydrangeas, the soil needs to be acidic. Remember that a lower pH indicates more acidic soil. To find out what your soil’s pH level is, the first step is to test it using a test kit or meter, or collect a sample and have it tested at your local extension office.
To change the pH level in your soil, there are simple additives that you can use. To make the soil more acidic (to change flowers to blue, or to make your blue Hydrangeas more vibrant), you can mix ¼ ounce of aluminum sulfate per 1-gallon of water to treat the soil 2-3 times per year.
If using aluminum sulfate, be sure to water your plant thoroughly and make sure that your Hydrangea is not newly planted. A plant that is not well-established can suffer root damage from this solution.
Another option is to use premade soil acidifiers. These pellets are great because they don’t require any mixing chemicals, and there are easy-to-follow instructions for making your blooms turn blue.
Whatever you use, be sure to rinse off any chemicals or product that gets onto your Hydrangea’s leaves or blooms to prevent any damage to the plant.
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02/18/2024 05:20 am GMT
How Long Does it Take for Hydrangeas to Turn Blue?
Changing the chemical balance in your soil is not an instant process. It’s important to have some patience and monitor your Hydrangeas after treating the soil.
It can take several months or even more than one growing season to get your soil suitably amended to produce the color blooms you’re hoping for.
Will My Blue Hydrangeas Stay Blue?
Your Hydrangeas will stay blue as long as the soil conditions remain the same. The best way to ensure that your blue doesn’t fade is to continue to test your soil each season or year.
You can also continue to supplement your soil with acidic fertilizer once per year in the spring. Or you can also use everyday compost items, such as coffee grounds, sawdust, peat moss, or other materials with higher acidic content to keep your soil at the appropriate pH level.
Can Blue Hydrangeas Turn Purple?
Purple Hydrangeas look whimsical in a way that soft pastels just can’t duplicate. If you have blue Hydrangeas, it’s easy to adjust their hue to make them more purple.
To shift your blue Hydrangeas to have a purple tint, you can amend the soil by applying garden lime during the fall months before the growing season. This will make the soil less acidic, so be careful. Too much garden lime will turn your Hydrangeas pink. You’re shooting for that sweet spot just between acidic and alkaline (a pH between 6 and 7).
Will Pennies or Vinegar Turn Hydrangeas Blue?
The practice of burying metals, like rusted nails or pennies, to change the Hydrangea’s color dates back a couple of centuries. Planting pennies alongside your Hydrangeas today might bring good luck, but it won’t change the color of its blooms.
Pennies were, at one time, minted using aluminum. Aluminum ions are necessary for the soil composition for blue Hydrangeas, but unless your pennies are all from a brief period during the 1970s, they don’t contain any aluminum.
Vinegar, on the other hand, can be useful for adjusting your soil’s pH. To make your soil more acidic (lowering the pH), you can mix vinegar with water and apply it to the soil around your Hydrangea.
Final Thoughts
Hydrangeas produce beautiful flowers that increase curb appeal and bring a luxurious or whimsical feel to your garden. Their ability to change color is very unique and something that you should take advantage of. Start with a simple soil test, and then have some fun doing your own garden chemistry. Remember, acidity and aluminum ions are both keys for blue Hydrangeas, so if you’re not getting the results you want, you may need to adjust one or both of these soil elements.
