Hydrangea color change is always a surprise to gardeners. You buy a plant with blue blooms only to discover later that the blossoms are now pink. Why does this happen and what can you do about it?
More importantly, hydrangea flowers can often change color, depending on your soil conditions.
The mop head or the lacecap varieties, as well as certain paniculata varieties, are some that change color depending on your soil structure.
Gardeners in the 18th century even experimented with hydrangea color change by burying rusty nails in the soil, pouring in tea, and even chanting spells over the plants!
Keep reading to find out why hydrangeas change color and what you can do to change get blooms the colors that you want.
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Why do hydrangea flowers turn blue?
The colors of hydrangea blossoms are affected by the acidity or alkalinity of the soil they are growing in.
An easy answer to your question of why hydrangea colors turn blue is: high acidity = blue blooms, while low acidity (or a more alkaline soil) = pink blooms.
This is one of the reasons that hydrangeas planted under pine trees often have blue flowers, since pine needles are acidic.
In order to find out your soil pH, a soil testing kit will come in handy.
Generally speaking, acid soil has a soil pH of lower than 5.5 – 6. If you use a planting mix formulated for acid-loving plants so the soil pH is lower to begin with you’ll get blooms that are blue or lavender-blue in color.
Alkaline soil, with a pH above 7.0 produces pink and red blooms. pH ranges between the two give you purple colored blossoms.
This hydrangea color pH chart shows how soil pH affects bloom color. The ranges are approximate but show the progression of acidity to alkalinity and bloom color.
However, it is not just the soil pH that affects color.
Acidic soil, where aluminum is available, will cause the hydrangea to bloom blue, whereas more alkaline soil will produce pink petals. It all depends on the amount of aluminum the plant is able to absorb through its roots.
Many methods said to lower the soil pH include adding come kind of organic matter. Vegetable and fruit peels, eggshells and grass clippings all help.
Some gardeners swear that adding coffee grounds (which are acidic) to the soil will make the soil more acid.
The thought is that the increased acidity makes it easier for the hydrangea plant to absorb naturally occurring aluminum from the dirt.
You can try certainly experimenting with adding coffee grounds to test changing the color of the blossoms. However, the beneficial effect will likely be more because of adding organic matter to the soil, than helping it become more acidic.
Do hydrangeas like coffee grounds? Yes, indeed! Coffee grounds are a natural acid-loving plants fertilizer. Roses love coffee grounds too, as do azaleas and camellias.Do you find that your blue hydrangea blooms have turned to pink? Find out why this happens and what you can do about it on The Gardening Cook. #hydrangeacolor #hydrangeas 🌸🌸🌸 Click To Tweet
Changing hydrangea color
It’s not unusual to see different colors of hydrangeas on one bush. Soil pH can vary even in one garden bed!
The real reason for the colors is not just the soil pH, though, it is because of a metal element – aluminum.
To get blue blooms, you need to have the right amount of aluminum in the soil, so that the plant can absorb it through the roots and up to the flowers.
Interestingly, it is easier to change a hydrangea color from pink to blue that it is to change one from blue to pink.
The reason is that it is easier to add aluminum to the soil than to take it out!
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How do I get blue hydrangea blooms?
To lower your soil pH for blue blooms, add garden sulfur or aluminum sulfate to your soil around your hydrangeas.
A recommended dose is a solution of 1 tablespoon of aluminum sulfate for each gallon of water. Water well in advance of the application. Be careful , too much of the solution can burn the roots of the plants.
Also make sure the plants are at least 2-3 years old. New plants are more susceptible to root burn.
Be sure to follow the directions on the product you use, and test your soil before and after adding the chemicals to make sure the pH is in the range you want.
Note: It may be necessary to apply the sulphur or aluminum sulfate several times. The hydrangea color change can take a few months to happen.
The fertilizer you choose for your hydrangeas can also affect their color change. If you want blue blooms, choose a fertilizers that is low in phosphorus and high in potassium. (25/5/30)
Avoid adding bone meal if you want blue blooms.
Also, don’t be too disappointed if your blooms don’t turn back to blue. Some varieties are resistant to change and white hydrangeas are stubborn. They like being white as these hydrangeas from the Wellfield Botanic Gardens show! There is not a hint of any other color here.
One interesting note is that planting hydrangeas very near to a side walk or concrete foundation makes it hard for the plant to get blue blooms. This is because lime leaches out of cement, making it difficult for blue flowers to form.
How to I get pink hydrangea blooms?
If you happen to like the pink blossoms, use ground lime (dolomitic lime) to raise the soil pH and make it more alkaline.
Aim for a soil pH of 6.0 to 6.2 and try to keep it below 6.4. Higher levels can cause an iron deficiency.
Another way to get pink blooms is to use a fertilizer with a high level of phosphorus. This helps to keep the aluminum from entering the system of the hydrangea.
If your soil naturally produces blue hydrangea blossoms, and you want pink ones, try growing hydrangeas in containers instead. You’ll be able to control the soil pH more easily this way.
You can use planting mix formulated for alkaline-loving plants so the soil pH is higher to begin with.
One thing to note is that you are unlikely to have luck with getting true red hydrangeas if you live in a hot climate. Temperatures seem to affect hydrangea color. No matter how much lime you add to the soil, the color is likely to be only a very deep pink rather than red.
Hydrangea color change FAQ
I get lots of questions from my readers about changing the color of hydrangea flowers. There are also lots of old wives tales about hydrangea color change.
I’ll try to cover some of them in the FAQ section below.
Does epsom salt make my hydrangeas turn blue?
Epsom salts are magnesium sulfate, and sulfur is a mineral that we often add to soil to lower the pH level.
Epsom salt contains ions which break down but they have a neutral effect on the pH of the soil when this happens.
Since the blue color of hydrangeas comes from the aluminum in acid soil, rather than just soil pH, adding epsom salt will not make your hydrangea flowers change color from pink to blue.
Will baking soda change the color of hydrangeas?
Baking soda is a common household ingredient that can be used in many ways in the garden. It has antifungal properties and is a natural disinfectant for lots of garden items from clay pots to tools and garbage bins.
A common question from readers asks about using baking soda to change the color of hydrangeas. Will it work? Well, it depends on the color you are looking for.
Baking soda is on the high end of the alkalinity scale. It can alter the pH level in the soil and might change the color, but not from pink to blue! Since blue flowers require acidic soil, adding baking soda may make your hydrangea flowers more pink!
This happens because adding baking soda to the soil alters the pH level to one that is more alkaline and gives you pinker flowers.
Coffee grounds for hydrangeas
Since coffee is acidic, so it makes sense to think that adding it to the soil will change the blooms of hydrangea from pink to blue.
However, adding coffee grounds directly to the soil around plants won’t make the soil more acidic.
This is because the acid in coffee is water soluble, so most of the acid is in the coffee itself. Used coffee grounds have a near neutral pH of about 6.5.
This is true for used coffee grounds. Fresh coffee grounds, on the other hand ARE acidic and adding these to the soil of acid loving plants like azaleas and hydrangeas can help to make the soil more acidic over time.
Are coffee grounds good for hydrangeas?
There are, however, lots of reasons to use coffee grounds around your hydrangeas. Since hydrangeas are acid loving plants, it makes sense to use coffee grounds in the nearby soil.
Coffee grounds are about 2% nitrogen by volume and all plants need nitrogen to perform well. They also contain potassium, calcium and magnesium as well as other other trace minerals.
Coffee grounds improve the structure of your soil. Adding any organic matter to soil helps it to drain moisture better.
So, while the coffee grounds won’t make the soil more acidic and probably won’t alter the color of the blooms, they will help the plant in other ways!
Will adding eggshells make my hydrangea color change to blue flowers?
There internet is full of gardening hacks and some gardeners advocate using eggshells to change the color of hydrangeas.
Eggshells are good for the soil around hydrangeas, since they contain calcium. This will make the plant stronger and will make it grow faster. However, this only works if the eggshell is ground into a powder.
Eggshell powder can change the pH of the soil but only if the soil is already acidic. When you add eggshell powder to the soil, you make it neutral. This means the color of the hydrangea flowers will be purple.
Also, eggshell powder neutralizes the action of aluminum sulfate which is needed for blue flowers so it is not helpful in turning the flowers blue.
Why are my hydrangea flowers turning green?
Hydrangea bloom turn different colors as they age. These blooms are from the same bush in the first picture at the top of this post. None are still blue.
No matter whether the plant starts out with pink or blue blooms, the most common color they will turn to is green.
The reason is that the sepals (the petal-like leaflets of the flower that protect the bud) are naturally green. As the sepals age, the other pigments of pink, blue, or white are overpowered by the green, so the hydrangeas fade to green as it matures.
This is especially true if you live in the South where it is hot and humid. This hydrangea bush is planted at my front door and had glorious dark blue blooms just a month ago. Look at the color now!
After turning green, they’ll likely add shades of pink and burgundy.
No matter the color of your hydrangea blooms, there is no denying that they make a beautiful plant.
Are you new to growing hydrangeas? Find out how to propagate hydrangeas in my guide which shows photos of cuttings, tip rooting, air layering and division of hydrangeas.
Pin this post for hydrangea color change
Would you like a reminder of this post for how to change the color of hydrangeas? Just pin this image to one of your gardening boards on Pinterest so that you can easily find it later.
Admin note: this post for hydrangea color change first appeared on the blog in June of 2013. I have updated the post to add all new photos, a printable project card, and a video for you to enjoy.
- Watering Can
- 1 gallon of water
- Aluminum Sulfate
- Garden hose
- Soil testing kit
- Be sure your hydrangea plant is 2-3 years old.
- Water well before adding the mixture.
- Place one tablespoon of aluminum sulfate into a gallon of water Mix well.
- This amount waters one mature hydrangea plant.
- Be patient. It can take 2-3 months for hydrangeas to change color and some varieties are resistant.
- You can also print out the color chart below of pH ranges and bloom color to add to your garden journal.
Be sure to follow the directions on the product you use. Be careful, too much of the solution can burn the roots of the plants.
Test the soil before and after use to get the pH in the range you want.
A fertilizer that is low in phosphorus and high in potassium can also be used to achieve blue blooms.. (25/5/30)
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