My mother-in-law hated blue hydrangeas and called them tacky trailer park plants. She poured hot grease from her kitchen on the roots, trying to kill them, but it never worked. Those blue blooms just kept coming, clashing with her glorious golden euonymus and red plastic poinsettias.
Changing Hydrangea Colors
If only she'd known the trick I'm going to tell you, she could have turned her hydrangeas pink—a color that goes so much better with red plastic poinsettias. She didn't need to adjust her attitude; she merely needed to adjust her soil.
You see, for most French hydrangeas (Hydrangea macrophylla), the flower color indicates the pH of the soil. In strongly acid soil (pH below 6), flowers turn blue. In alkaline soil (pH above 7), flowers turn pink or even red. In slightly acid or neutral soil (pH 6 to 7), blooms may be purple or a mix of blue and pink on a single shrub. Keep in mind that selections vary in their sensitivity to pH. For example, 'Ami Pasquier' stays crimson in all but the most acid soil and 'Purple Tiers' remains purple.
What about white hydrangeas? Sorry, they don't play along. They stay white regardless of the soil pH.
Okay, here's the trick I promised you. To make soil more acid, sprinkle ½ cup garden sulfur over the soil beneath the hydrangea, and water it in. To make it more alkaline, do the same with ground lime. Endless Summer Color Me Pink and Color Me Blue products (available at garden centers and from naturehills.com) supply pelletized lime and sulfur respectively. Depending on the size of your plant and your soil conditions, you may need to apply it several times. Be patient; results may take months.
Choose Your Hydrangea Color
These six hydrangeas are widely available and are some of our favorites. Your soil may affect the hue.
'Ami Pasquier': Crimson flowers in all but very acid soil, where it turns a wine purple color. Lacecap type.
'Ayesha': Distinctive cupped petals are eye-catching. Pale pink to light blue. Very glossy, deep green leaves. Mophead type.
'Endless Summer': Repeat bloomer flowers on old and new growth. May be blue or pink. Mophead type.
'Madame Emile Mouillere': Vigorous and dependable. Widely considered to be the best white. May rebloom. Mophead type.
'Nikko Blue': Dependable and cold hardy, it's a longtime favorite and widely planted. Turns pink in alkaline soil. Mophead type.
'Purple Tiers': Beautiful double-flowered lacecap type. Water lily-shaped blooms are deep purple in acid soil and pink in alkaline soil.
Making Cut Hydrangea Flowers Last
French hydrangea blooms are so gorgeous in the garden that it's only natural to want to cut them to display on your porch or bring inside. But it can make you go nuts when the blooms wilt an hour after they go in water. How can you stop this?
Here's an idea from Elizabeth Dean of Wilkerson Mill Gardens (hydrangea.com), a fine mail-order source for hydrangeas. Plunge the cut stems in cool water immediately after cutting. Pour about 1 inch of boiling water into a container, and let it cool for a minute or two. Cut the stems to the lengths you want for your arrangement. Hold the bottom 1 inch of the stems in the hot water for about 30 seconds. Then transfer the stems to cool water. Done!