Hydrangea plants can be confusing. There are lots of varieties, some of which have bloom colors that can be altered. Here’s the inside scoop to determine if yours is a variety that can be changed. If it is, we’ll show you how to change hydrangea colors in your landscape.
First, a snapshot of hydrangea groups to help determine if yours is a type of hydrangea with flower colors that can be modified.
Bigleaf or Macrophylla | Hortensia Hydrangeas
These plants are famous for their ability to change flower color. Focus here if you’re yearning for blue or pink blooms.
Mopheads are the darlings of gardeners across America, happy in a variety of growing zones (check cultivar) and perfect for both landscape use. these are also excellent for cutting. The flowers of mopheads are rounded, often very large and span a wide range of blue and pink shades.
These are also referred to as French hydrangeas. Florist’s hydrangeas are another name for these, particularly dwarf varieties in this group, ones that aren’t especially winter hardy.
Lacecaps have earned their name because of their flower form. These are flattened central clusters of “lacy” fertile blooms, ringed by a circle of larger sterile flowers. Lacecaps, like the mopheads, have flower colors that can be changed by adjusting soil acidity.
Smooth or Aborescens Hydrangeas
Midsize landscape shrubs, these hydrangeas produce large to huge white blooms.
The famous Annabelle is the most widely recognized member of this group. This cultivar is winter hardy from zones 5 through 8 and is coveted by florists for over the top cut floral designs. Annabelle also makes an outstanding flowering hedge, especially for sites with a bit of shade.
Cone shaped flowers and larger shrub to tree size forms are found in this group. Flower colors vary from green to white and often mature to antique pink. The colors typically change with maturity so it is common to have different flower hues on the same plant over the course of the growing season.
These are great plants for cut flowers and for blooms to use for drying. While hydrangea paniculata flowers may turn pink as they age, they do not change color based on soil adjustments.
Climbing or Petiolaris Hydrangeas
This group really has only one member, a climbing variety that produces white flowers on vines that can grow to more than 50 feet. Slow to get going, climbing hydrangeas are stunning as mature plants because of their size, long lasting blossoms and attractive form.
Climbing hydrangeas flowers are similar to lacecaps but these are always creamy white.
Oakleaf or Quercifolia Hydrangeas
Flowering with long clusters of white blooms, oakleaf hydrangeas are easy care landscape choices. Their foliage is distinctive and looks very much like classic oak leaves. It even takes on the attractive red or orange autumnal coloring associated with oak trees.
Okay, now that you know the basics for identifying hydrangeas, let’s look at how to change flower colors.
How to Change Hydrangea Colors: It’s All About Soil pH
Hydrangea flowers – mopheads and lacecaps – display varying flower colors based on soil acidity or alkalinity. Acid soils produce blue flowers. Pink flowers are the results of basic, or alkaline, soils.
How do you determine relative pH of your soil? Do a fizz test.
Know What You’ve Got -Testing Soil for pH
Scoop a quarter cup of soil from the area where you want to plant. Remember that the plant roots located several inches below the surface, so get your sample from several inches down. Or gather soil from several spots within a three to four foot circle and mix to ensure a representative sample. Remove any rocks, sticks or other debris.
Place half the soil in each of two glass bowls.
First we’ll test for acidity. Add enough distilled water to one bowl to just cover the soil. Next, get a teaspoon of baking soda. Get ready to listen for little pops and to watch for fizzing. Okay, stir the baking soda into the sample bowl. Any fizzy activity? If so, your soil leans to the acidic side of the pH spectrum.
If there was no fizz with the acidity test, next we’ll test for alkalinity. Get your second sample soil bowl and add enough standard household white vinegar to cover the soil. Look for the same fizzing activity as in the previous test. If the vinegar produces little pops and fizzing, that reaction indicates your soil tends to be alkaline.
If there was no reaction with either test, your soil is neutral.
Now that you know about your landscape’s pH, what’s next?
Amending Soil to Change Hydrangea Colors
Increasing Soil Acidity
The fastest and easiest way to acidify soil is with the addition aluminum sulfate. Follow box directions for amount to use and work into the soil with a trowel being careful not to damage the roots. Or mix 1/4 cup of aluminum sulfate into one gallon of water and use as a soil drench. This mineral is also good for hollies, azaleas, camellias and other acid loving plants.
Natural ingredients such as coffee grounds, crushed egg shells and chopped up citrus peels may also be used, they’ll just take longer because they’ll need to decompose before effecting the soil.
Increasing Soil Alkalinity
To encourage hydrangeas to bloom with pink flowers, add garden lime. This powder raises the soil pH and “sweetens” the soil. Garden lime has been used by farmers for generations to aid plants with uptake of a number of minerals and soil nutrients. Again, follow label directions.
You’ve Got It
That’s it! Now you know how to identify hydrangeas with flower colors that can be changed. And how to test your soil for that oh-so-important pH. And finally, how to change hydrangea colors in your garden.
Ready to choose some hydrangeas? Go here: Spring hydrangeas for sale.
In love with hydrangeas and interested in learning more? Hop over to the website for the American Hydrangea Society.