How To Lower Your Soil's pH and Turn Hydrangea Flowers Blue

by dustytoes

For some types of hydrangeas the flowers can be turned from pink to blue by changing the soil's pH, making it lower, or more acidic.

How do I turn my hydrangea flowers blue? This is a question asked by many growers of this favorite perennial. The first thing you should know is that not all types of hydrangea flowers have the ability to change color. Only the macrophyllas will change flower color according to the type of soil in which it's grown. Knowing the pH of your garden soil will an indication of what bloom color to expect.
If your dirt turns out to be too alkaline to grow anything other than pink flowering hydrangeas, there are amendments that can be made to the soil to lower the pH and thereby change the petals to that pretty blue you want.
However, this is not a quick fix and it may not be permanent without a lot of work, and a better option may be to grow them in pots.

Making The Flowers Blue

It's not a simple fix.

blue hydrangea flower

In a nutshell, here is what you need to do when planning to grow blue hydrangeas.

  • Test the pH of the area of the garden or yard where you plan to plant the shrub.
  • Select a product to lower the pH if it's above a six.
  • Follow the directions on the package (of whichever product you choose - some are listed on this page) for amending the soil.  Don't overdo it, and realize that it may take some time for the pH to change.
  • If the plant is already in the ground, do not be overly aggressive with treatment as you could damage the plant.

Of course the flowers may be a variety of colors (including pink) if certain roots are feeding off the more alkaline parts of the soil.  The blue flowers will also fade and become various shades of pink, purple and even green, in my experience. 

You may want to consider growing your blue hydrangea in a pot, using store bought dirt, with peat moss, and lots of organic matter added.

Test the Soil Yourself

The kids that are available are easy to use.

There are a couple of ways to text your own garden soil.  Buy a do-it-yourself kit and compare the results to a chart, or send a dirt sample off to an agriculture extension office to have it tested for you.

Hydrangeas are hardy perennials and they will grow fine in either alkaline or acid conditions, but knowing the alkalinity of the planting zone, will determine flower color.

A soil testing kit can help with growing all types of things, from trees and shrubs to vegetables and fruit.  When fertilizing and watering doesn't seem to help, maybe the trouble is in the soil.


Get to Know Your pH Levels and Grow Better Shrubs, Trees and Flowers

Certain plants do well in certain types of soil, and the only way to know your soil is to test it!
Luster Leaf 1612 Rapitest pH Soil Tester
$8.99  $4.67
Hydrangeas lining a road in Norfolk, England
Hydrangeas lining a road in Norfolk, England

Only The Macrophylla Hydrangeas Can Have Blue Flowers

You may know them as 'mopheads' or 'big leaf'.

big leaf hydrangeas

Not all types of hydrangeas can have blue flowers. The type that has a changing flower color is the macrophylla. It gets it's name from the size and shape of it's leaves.  'Macrophylla' means long, or large leaves. 

To the best of my knowledge, this is the only type of hydrangea that will have blue flowers if it's grown in soil with a pH that is below six.

These plants are deciduous, and will have bare branches in winter.  Don't cut them down!  New growth will appear along the stems in Spring.

Hydrangeas of this variety will usually have roundish, ball-shaped, flower heads.  The exception is the lacecap, which has a more flattened looking flower and appears to be only partially in bloom, when in fact it is in full bloom. 

The paniculata variety has flowers that will not change color due to soil pH.

Use a Reliable Product to Lower pH

A safe way to change the soil, this amendment will help anything that prefers acidic over alkaline.

I have never used this sulfur additive because I don't need it where I live.  In my area of New Hampshire, and probably most of New England, the soil is acidic enough to grow blue-flowering hydrangeas.

The only exception may be when they are grown near buildings where limestone leeches into the soil around the foundation.

I do buy the Espoma Bone Meal to build sturdy roots, and I like this brand.  The reviewers who purchased it were happy with the results in growing blueberries, but the bag states that it "turns hydrangeas blue".  If you grow blueberries, use it there as well!

Use Organic Garden Sulfur to Amend The Soil and Lower pH

Espoma Organic Traditions Soil Acidifier(Garden Sulfur) -...

A Word of Caution When Using Sulfur

Make sure you add sulfur correctly.

From what I've read about amending the soil with some type of sulfur to lower the pH, it must be added carefully and then worked well into the soil at a depth of at least six inches.  This can be tricky when trying to add it around a shrub that is already in the ground.  Doing it before planting would be the best option.

If you want to change the soil type in a large area, know the dimensions before buying sulfur.  There should be charts at the store for figuring how many pounds of sulfur to buy.  The sulfur reacts with bacteria already in the soil.  The bacteria breaks down the sulfur to increase acidity and this process can take weeks or even months.

Have you successfully changed your hydrangea flower color to blue?

What worked for you?
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Sphagnum Peat Moss

Hoffman 15503 Canadian Sphagnum Peat Moss, 10 Quarts

Premium grade of horticultural canadian sphagnum peat moss is 99.8 percent organic. When mixed with soil, increases the soil's capacity to hold water and nutrients. Can be blend...

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More Ways to Change Your Soil's pH

Organic matter makes for an acid type environment.

A high lime content makes soil more alkaline.  Adding compost will help bring down the pH.  Adding leaves, pine needles and bark mulch that has a more acid content will help also.   Sphagnum peat, or peat moss, is another good alternative and will help loosen up soil while bringing down the pH level.

Hydrangeas That Grow Indoors

Choose a mophead variety and put it into a pot, and let me know how it does!

I've never grown a hydrangea indoors.  I don't know what would happen to it over winter - would I have a bunch of leafless sticks to look at?  Does it have to stay in a cold place?  If it's inside, will it bloom again next year? 

If you know the answers to these questions, please leave a comment!

More About Soil pH and Either Raising or Lowering It

These are good sources for more in depth info related to this page.

Organic Gardening - How to Lower Your Soil pH
Learn the basics of pH levels and how to fix them for your growing needs.

How to Adjust Soil pH For Your Garden
Charts and information on raising or lowering garden pH for growing things in general.

Changing Soil pH
About pH, and why it should be optimal for growing certain vegetables. How sulfur works to lower pH and charts to determine how much will be needed to do so.

Updated: 03/19/2014, dustytoes
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dustytoes on 03/05/2015

Maybe they were in the wrong spot Sheila. All but one of mine are doing well - except that the deer eat the paniculata type (long flowers).

sheilamarie on 03/05/2015

I love hydrageas, but haven't had much luck planting them. I need to try again.

dustytoes on 03/11/2014

The color can't be changed in all varieties, but in some it can. Glad you learned something here.

VioletteRose on 03/10/2014

Love hydrangea flowers and I have grown both pink and blue varieties. But I had no idea the color was related to the pH of soil, thanks for sharing!

dustytoes on 11/15/2013

@Ologsinquito ..Thanks very much for that Pin !

ologsinquito on 11/15/2013

This is useful for so many people who grow these beautiful flowers. I've pinned it to my "Things You Really Need to Know" board.

dustytoes on 07/18/2013

Thanks for reading, chevril.

chevril on 07/17/2013

I didn't know that only certain types could turn blue. Facinating article!

dustytoes on 07/02/2013

@Maggie... Welcome to the hydrangea lovers club!

MaggiePowell on 07/02/2013

I have always wanted to know how to do this! I love hydrangeas.

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