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LeBeau Bamboo Nursery      Medford, Oregon 541-499-4992

Make Your Hydrangeas Blue or Pink

Blue flowers on a dense Hydrangea

Selecting Varieties

With literally thousands of varieties across many different species, Hydrangeas offer an extensive pallet of styles, patterns, and colors to match any need in your garden. But on top of the already bursting number of choices available, many varieties provide you with the ability to wildly change the color of the flowers just be amending the soil the plants are growing in. Many Macrophylla or French Hydrangea varieties can be made to bloom deep blue, light blue, light pink, or deep pink depending on the pH of the soil.

Hydrangea plant with deep pink flowers.
The variety you start with makes a big difference in the intensity of the colors you achieve as well as how easily it can be brought out. Glowing Embers and Brunette both tend to be very dark pink and even red without having to amend the soil under most conditions. Pink Cloud Hydrangea typically produces very light colored flowers which can be either very light pink or very light blue, and Bridal Bouquet produces pure white blooms under almost all conditions. Nikko Blue and All Summer Beauty both produce deep blue flowers much easier and so are a great starting point if you want to grow blue Hydrangeas.

'Harlequin' Hydrangea produces multi-colored petals, the darker colored interior of each petal can be changed to either pink or blue.
If you are aiming for one color or another, it will be much easier and far more rewarding to start out with varieties that are going to work with you rather than against you.

All You Need To Do Is Change The pH Of Your Soil

The pH (or acidity) of your soil will dictate the color of your plant's flowers. If you turn your soil towards acidic then you will start seeing blue flowers, or if you soil is neutral to alkaline then you will see pink flowers. A more extreme pH will yield a darker and more intense color. Changing the pH of your soil is actually quite easy and can be done by adding a single ingredient into your soil. For acidic soil and blue flowers you can mix in aluminum sulfate which can be purchased in the gardening section of almost any store. Aluminum sulfate is very commonly used for achieving blue flowers across many different plant types but is most often used for Azaleas and Hydrangeas. If you are looking for an organic alternative then you can apply used coffee grounds to your soil.

To produce pink flowers then add a base to your soil such as ground lime. This is literally ground up limestone rocks - this is a fantastic amendment to soil because in addition to making the soil more alkaline it also provides essential calcium to your soil.

Very light pink blooms produced in neutral soil. This variety, 'Pink Cloud' produces lighter colored blooms on its own anyway.
Specific pH Targets
For blue you are targeting a pH of between 5 and 6 while you are targeting 7 to 8 for pink flowers. A handful of aluminum sulfate or coffee grounds will make your pH go down a bit and lime will make it go up. You can purchase pH test kits for relatively cheap to get the exact starting number, giving you a better estimate for how much of either amendment to add. However if you already have the ingredients and want to get out into your garden today then just go ahead and add one of your adjusting amendments. After your Hydrangea plants bloom the flower color will give you a rough idea of how much adjusting is left to do. If they are not blue enough then add more aluminum sulfate, or lime if they are not pink enough. Just take it slow so you don't adjust the pH to an extreme and hurt your plants. For a Hydrangea in the ground, add a handful of your amendment and water it in around the base of the plant. It should start to affect the color within a month and then if needed add another handful. If you go too far on either end and your plant starts to suffer, add a handful of the opposite adjuster and the pH will be balanced.

Over time, any amendments you add will likely be washed away so you might need to add another handful every couple of years to maintain your desired color pallet. This is especially true for Hydrangeas grown in containers where water washes nutrients out much more quickly, so you will likely need to add a handful every year for potted plants.

Which Hydrangeas Does This Work On?

Changing the flower color based on soil pH works really well for French Hydrangeas, which are varieties with the species Hydrangea macrophylla. These are also known as Bigleaf Hydrangeas and produce two distinct flower forms, the more popular rounded mophead type as well as the lacecap type. Changing the color works pretty well on both mophead and lacecap flower types but in general it seems easier and more vibrant with the mopheads, at least in our climate. Some French Hydrangea varieties are quite stubborn with their color and more resistant to pH changes, again the best examples are 'Glowing Embers' which wants to be red or pink or 'Nikko Blue' which wants to be blue. But most varieties with more neutral colors can be changed easily.

Most other species of Hydrangea have much less color change than Hydrangea macrophylla. Hydrangea arborescens, anomala, quercifolia, paniculata, aspera and about 70 other species have little color change based on pH. However, Serrated Leaf Hydrangeas in the species Hydrangea serrata can also be changed like the French varieties because they are closely related.

H. serrata 'Kiyosumi' is a lacecap type that can also be changed, this one is grown in soil with a pH around 8 and the margins are nearly red.

How This Actually Works

pH is a measurement of the acidity of (in this case) your soil, which can be acidic (low pH), neutral (pH around 7), or alkaline (high pH). The pH of soil greatly affects how a plant's roots absorb nutrients and can determine which nutrients are actually available to the plant. The nutrients absorbed by the roots are very important to various functions and chemical processes within the plant, and some of these related processes include the production of pigments. Changing of the pH of the soil is an easy way to alter the plant's internal chemistry and modify which pigments are produced and when, therefore dictating the color of flower petals.

You want to adjust your soil's pH enough to produce the desired color change but not so far that you cause problems with nutrient absorption overall. We all know what plants look like when they are missing essential building blocks - without enough nitrogen plants are not able to produce enough chlorophyll and turn yellow. And grow really, really slowly because chlorophyll is what allows photosynthesis to occur and without that plants will have very little going on.

Plain white Hydrangeas are pretty awesome too! This is 'Annabelle'

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