Turning Hydrangeas Blue or Pink
You say you want your hydrangeas to be in the pink or feeling blue? Success depends on what type of hydrangea you have and the pH of your soil.
White: Some hydrangeas will never change color. A white ‘Annabelle’ will always have white fading to green flowers. Limelight will always be green that turns white and then pink, and varieties of Hydrangea paniculata, such as the old fashioned Pee Gee, the new Bobo, ‘Tardiva’ and ‘Little Lamb’ will produce white flowers that age to pink. There is no way to make these varieties turn blue. Most mop heads (H. macrophylla) and lace caps (H. serrata or H. macrophylla normalis) hydrangeas can be made blue or pink.
Blue: It’s the aluminum in the soil that turns hydrangeas blue, but the plant only absorbs this element in acidic soils. So if you want blue hydrangeas you need to have acidic soil. On Cape Cod the ground is naturally acidic so hydrangeas will be blue if we do absolutely nothing unless the pH is being changed by lime from lawn applications or proximity to concrete. When this is the case you can use sulfur or aluminum sulfate to lower the pH again, but be careful to apply according to directions! Too much aluminum sulfate will burn plants. If the native conditions favor alkaline soil, and you want your hydrangeas to be blue, you’ll need to apply an amendment around your plants that will turn that soil acidic. The most common product sold for this purpose is aluminum sulfate, but sulfur can be used as well. No matter which you choose, be sure to apply the product according to directions. Too much can harm your plants.
Pink: When your soil is acidic and you want your hydrangeas to be pink, you’ll need to spread lime and/or wood ashes around your plants. In some areas it might be necessary to apply a good amount of lime twice a year in order to keep the soil alkaline. In either case, the change in flower color won’t be instant. If your flowers are already blue you might have to wait until the next summer to see pink petals appear.
Multi-colored: Can you have a Hydrangea with some blue and some pink flowers? Absolutely. Just divide the area around your shrubs into quarters, and amend the soil on two opposite sections to create alkaline conditions and on the other two areas to make the dirt acidic. Be sure to note which area is which so you don’t end up switching and canceling out the blue or pink effects. Finally, some amount of the color you see on a hydrangea is due to genetics. A ‘Nikko Blue’ Hydrangea will always be light blue or light pink, never dark purple. In most cases you can change the color but not the intensity of that hue.
Myth Busting: Hydrangea color has nothing to do with rusty nails, nickels or any other metal debris that is put around the shrubs.
Truth Telling: Color on the and blue and pink varieties will last longest when the plants are put in an area where there is morning sun and afternoon shade. When planted in full sun the flowers will bleach out and turn brown fairly quickly.
Don’t Worry: Sometimes people wonder why the hydrangea they are buying in our nursery is pink when what they want is blue. This happens because they are raised in a neutral pH potting soil. As long as thesplants are put into acid soil they will bloom blue the next year. If you want to be sure the soil is acidic, have a pH test done at the Cape Cod Cooperative Extension.
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