Botanical Names: French or bigleaf hydrangea (Hydrangea macrophylla), oakleaf hydrangea (Hydrangea quercifolia)
Give your garden a splash of cooling blue by growing blue hydrangeas. Blue flower tones appear in the French or bigleaf hydrangea. When you grow blue hydrangeas, you bring that elusive hue right into the summer garden, a welcome break from the season’s sizzling shades. You can also learn how to make hydrangeas blue, shifting pink blossoms to blue shades.
It might sound like magic, but it’s true. With some Hydrangea macrophylla varieties, you can change flower color based on soil pH, which means you can make pink hydrangeas turn blue — or turn blue hydrangeas pink. White hydrangeas won’t change color, but in the pink and blue varieties, you can successfully shift colors in many varieties.
The color in a Hydrangea macrophylla flower comes about due to soil pH. You can turn down the pink tones on French hydrangeas by trying several things. Adding aluminum sulfate several times a year to soil where the hydrangea is growing helps lower pH, which makes aluminum readily available to plant roots. When plant roots absorb aluminum, petal colors take on blue tones. If your soil is naturally acidic, your hydrangea blooms will tend toward blue and purple shades.
Soil pH doesn’t shift overnight to produce the accompanying flower color change. It’s more of aprocess that can take several growing seasons. It’s vital to continue if you have any hope of keeping hydrangeas blue. When you use aluminum sulfate, plants should be two to three years old and established. Water the plants well before applying the solution, thoroughly wetting soil.
Apply the sulfate carefully and slowly, because it can burn roots. Other gardeners add coffee grounds and composted oak leaves to soil around hydrangeas to help lower pH and make hydrangeas blue.
A classic French blue hydrangea is ‘Nikko Blue,’ which has light blue mophead type flowers. If you want a light blue hydrangea with lacecap flowers, look for ‘Twist ‘n’ Shout’ and ‘SummerLace.’ ‘Blue Wave’ hydrangea is another light blue lacecap hydrangea.
For a deep blue mophead, look for ‘Blue Heaven,’ which is a Forever & Ever reblooming
hydrangea, opening flowers from spring to fall. ‘Mathilda Gutges’ has deep blue mophead flowers up to 8-inches across. It grows roughly 5-feet tall and wide. In deep blue lacecap hydrangea varieties, look for ‘Nightingale’ or ‘Fasan,’ a Swiss hydrangea that’s often sold and shown in its pink form. It does, however, make an impressive purple to blue hydrangea in acidic soil.
It’s important to note that blue hydrangeas with the deeper pigments tend to withstand more sun, which gives you a little more versatility in siting them in your garden. If you’re dealing with sunnier planting options and you want blue hydrangeas, aim for the ones with deeper blue tints and even purple hydrangeas.