Not all hydrangea flowers can change color, but, if you start with the right variety and expose it to the right conditions, it is possible to change some flower colors from pink to blue or blue to pink. I have provided step-by-step instructions below.
Not sure what type you are growing? See How to Identify Your Hydrangea to figure it out.
How to Change Hydrangea Bloom Colors
Can you change the color of hydrangea flowers from pink to blue or blue to pink?
It’s a common misconception that all hydrangeas can change colors. They cannot. And the ones that can shift from pink to blue or blue to pink require the right timing and conditions.
- The hydrangeas that can shift colors include some Bigleaf hydrangeas (Hydrangea macrophylla) and Mountain hydrangeas (Hydrangea serrata) varieties. You can see pictures of them below.
- With those varieties, start with plants with medium or light pink or blue flower color values.
- Deep red and blue colors will not change. White and green flowers will not change.
- To work, you will adjust the soil pH level and control the availability of aluminum in the soil. There is more on this below.
- For long-term results, this mean growing the hydrangea in a container where you can control the soil conditions ongoing, not in the ground.
- Following these tips, your hydrangea flowers (known as sepals) will gradually change color.
- It may take a year or more depending on the original soil pH level.
- Also, itโs easier to shift pink flowers to blue than blue to pink.
Contents
- Hydrangeas That Can Change Color
- Hydrangea Garden Myths
- Hydrangea Color pH Chart
- How to Turn Pink Hydrangeas Blue
- How to Turn Blue Hydrangeas Pink
- Frequently Asked Questions
- Resources
Hydrangeas That Can Change Color
Big Leaf Hydrangea
Hydrangea macrophylla
Light pink, purple, or blue varieties only.
Also known as ๏ฌoristโs hydrangea, hortensia, mophead, French, or lacecap.
โข Hardy to USDA zone 5
โข Bloom on old wood: do not prune, protect in winter
Proven Winnersยฎ varieties include:
Abracadabraยฎ series, Citylineยฎ series, Edgyยฎ series, Letโs Danceยฎ series, Parapluโข
Mountain Hydrangea
Hydrangea serrata
Light pink, purple, or blue varieties only.
โข Hardy to USDA zone 5
โข Bloom on old wood: do not prune
Proven Winnersยฎ varieties include: Tuff Stuffโข series
Hydrangea Garden Myths
There are plenty of myths about changing hydrangea flower colors.
Some of these include burying pennies or rusty metal in the soil, or adding pine needles, coffee grounds, Epsom salt, vinegar, or aluminum foil near a hydrangea plant.
Spoiler Alert: none of these work.
See Popular Garden Myths We Have All Fallen For for more (popular) garden misinformation and folklore.
Hydrangea Color pH Chart
Hydrangea Color pH Chart
Only Bigleaf / Mophead (Hydrangea macrophylla) and Mountain (Hydrangea serrata) hydrangeas can shift color in response to changes in soil pH.
| Blue flowers | pH 5.5 or lower | Aluminum available |
| Purple flowers | pH 5.5 to 6.5 | Some aluminum available |
| Pink flowers | pH 6.5 or higher | No aluminium available |
How to Turn Pink Hydrangeas Blue
To make the change from pink to blue, grow the plant in a container and lower the soil pH level to 5.6 by adding aluminum sulfate.
Choose the Right Type of Hydrangea
Start with Bigleaf (H. macrophylla) or Mountain (H. serrata) hydrangeas with medium or light pink, purple, or blue flowers.
Grow in a Container
Grow the hydrangea in a container. This makes it much easier to control the growing conditions long-term. Trying to change the pH of garden soil is a lifelong battle and not worth the effort.
Use Good Potting Mix
Use a good commercial potting mix suitable for shrubs and a low phosphorus-high potassium fertilizer (25-5-30), otherwise the phosphorus will lock up the aluminum.
Monitor Your Soil pH Level
Measure your soil pH level to gauge where you’re at and how long it may take. It’s a gradual process and you can’t push it without harming the plant. At 5.6 or lower, the shift to blue becomes visible.
Options: use test strips like these ones: Garden Tutor Soil pH Test Strips. Another brand is Fisherbrand Plastic pH Indicator Strips.
If growing in the ground (not recommended because results are not sustainable), another option is to contact your local university extension office or lab that does soil tests to find out the known range for your areas or lookup aerial pH maps.
You could also use physical clues: if hydrangeas stay blue in your garden, that’s a good indication the soil pH is right where you want it.
Add Aluminum Sulfate If Needed
Water the plant deeply (to avoid burning roots with next step) and then apply an application of aluminum sulfate Al2(SO4)3, also called powdered alum, following the product instructions.
You can find this online or at a plant nursery. There are also similar products for this purpose at plant nurseries: Color Me Blue or Color Me Pink.
The sulphur (sulfate) will bring the pH level down, making the aluminum available to the plant but it is a slow process taking months or longer.
Your product should have instructions. Otherwise, do this:
- For longest lasting-results, use a half-application (e.g. 1.5 teaspoons aluminium sulfate in one gallon of water) in fall and again at bud break in spring.
- Repeat annually as needed.
- Always check the package for precautions and instructions.
Alternately you can do just one application per year.
Either way, more is not better: too much aluminum will kill the plant. And each plant has a limit to how blue it will get.
Take Photos to Monitor Changes
Photograph your plant at the start or match the color to paint chip and check progress over the next year.
Once the pH level is lower than 5.6, the color change becomes visible.
How to Turn Blue Hydrangeas Pink
To change flowers from blue to pink, grow the plant in a container and make the soil pH more alkaline by adding garden lime (calcium hydroxide, Ca(OH)2). Your product should have instructions for correct application amounts.
This will stop the plantโs ability to absorb any aluminum present. Without aluminum, the color shifts to pink.
- Pink= Aluminium not available / alkaline pH level (6.5 or higher).
- Purple = Some aluminum available + pH between 5.5 and 6.5.
- Blue Flowers = Aluminium present + acidic pH level (5.5 or lower).
Frequently Asked Questions
Not all hydrangeas can change color but the flowers that do can take a year to shift from pink to blue or blue to pink.
Two varieties can change color if conditions are right. These are Hydrangea macrophylla, also known as Big Leaf or Mophead hydrangeas, as well as Mountain hydrangea (Hydrangea serrata).
No, you cannot change the color of hydrangea flowers by putting pennies or any other metals in the soil. This is an old garden myth.
No. Any effect on soil pH from pine needles is temporary. This explains why pine needles are not effective for changing soil pH long-term.
Blue hydrangeas need a soil pH of 5.5 or lower (acidic soil) with aluminum available in the soil.
Hydrangeas are light purple, a combination of pink and blue, when soil pH levels are between 5.5 and 6.5 and some aluminum is available.
Pink hydrangeas need soil pH of 6.5 or higher (alkaline soil) with no aluminum available.
Changing hydrangeas from pink to blue requires lowering the soil pH level to 5.5 or lower using aluminum sulfate.
Some hydrangeas can change from blue to pink by making the soil pH more alkaline (6.5 or higher) using garden lime (calcium hydroxide).
Resources
Hydrangea | Genus: Hydrangea
Flowering plants native to Asia and Americas
โข Hardiness Zones vary from 3 to 9
โข Morning and part sun
โข Soil: does not like to dry out
โข Fertilizer: Holly-tone by Espoma in spring only if required.
โข Propagation: How to Root Hydrangea Cuttings
โข Pruning: Need to prune depends on variety
โข Pink/Blue: See how color changes
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Read More
- Role of aluminum in red-to-blue color changes in Hydrangea macrophylla sepals
- Proven Winners – Blue Hydrangeas
- Proven Winners – Hydrangeas Demystified
- Soil Acidification: How to Lower Soil pH
It’s an interesting plant! Let me know how your color change goes.
~Melissa the Empress of Dirt โ
How to Change Hydrangea Flowers From Pink To Blue
Supplies & Materials
- 1 shrub Hydrangea Bigleaf or Mountain
- 1 bag Aluminum Sulfate
Instructions
- Plant hydrangea in container with suitable potting mix.1 shrub Hydrangea
- Test soil pH and record value.
- Take photos of any flowers that form from now onward.
- In fall, water plant thoroughly then apply half dose of aluminum sulfate per product instructions (usually 1.5 teaspoon in 1 gallon water).1 bag Aluminum Sulfate
- Overwinter plant as needed to protect from freezing temperatures.
- In spring, at bud break, apply another half dose of aluminum sulfate.
- Measure soil pH every few months and compare.
- When pH is 5.6 or lower, hydrangeas can take up aluminum in soil and gradually turn light blue.
Claire Daniel says
Thank you so much.
Mary Lou Mayfield says
Because I live between zone 4 and 5, I have to cover my bigleaf Hydrangea in the fall. This requires cutting it back, which you do not recommend. What do you suggest?
Melissa J. Will says
Is this your first year with it or has it already survived previous winters? I would not cut it back. I would insulate it with something like straw or leaves secured in place with burlap.