Why Aren't My Hydrangeas Blue?

By Teresa Opdycke

The first time I crossed over the Sagamore Bridge and began winding down 6A on Cape Cod, my mouth dropped open and I shouted, "Why aren't my hydrangeas blue?" The most beautiful, enormous, spheres of blue hydrangeas taunted me around every bend in the road. The hydrangeas I’d seen in my area of Ohio were mostly white with one gorgeous pink coquette flirting at the world from her abandoned home. I was shocked and amazed at the lovely shrubs of blue. All that blue inspired me and I vowed to learn more about hydrangeas of ocean blue.

Hydrangeas are woody shrubs brought back from Japan by happy wanderers and introduced to the American scene sometime in the 1730s. A few Frenchmen started raising seedlings in pots and discovered that while the plant was young, it would produce large mop head blooms that enchanted gardeners and onlookers and became wildly popular.

Hardy in zones six through ten, hydrangeas tend to be a bit fussy about where they live. As I discovered, after being wowed by Cape Cod hydrangeas, the color is in the soil. A bit of an over simplified statement, but true. Without further adieu, here's the dirt on color and hydrangeas.

1. If you have a white hydrangea, appreciate it for what it is. No matter what you do to the soil, it will remain white except for a touch of pink or deep red that sometimes appears on the florets as it ages.
2. Depending on the variety of hydrangea and uncontrollable weather patterns, the intensity of color varies from plant to plant if not head to head. There’s nothing you can add or detract to achieve a more vibrant color. Fertilizing once or twice a year boosts the health of your hydrangea, which in turn may give it a bit more brilliance.
3. There are, of course, pink varieties and blue varieties of hydrangeas that can be purchased from nurseries and growers. Even a pink hydrangea will lose its lovely pink color if the soil is not just what it needs.

Let's say you have a pink hydrangea and want it to bloom in similar Cape Cod shades of blue. What do you do? Keeping a pink hydrangea blue in an alkaline soil requires constant attention to what’s going in the ground around the plant. As soon as soil conditions revert back to the natural state for your area, it will revert back to a pink color.

Still just got to have a blue hydrangea even if the soil where you live contains chalk? Blue hydrangeas require aluminum to be in the soil for them to bloom the color of a newborn’s eyes. Check the pH level of the ground around the hydrangea plant; for a blue flowering hydrangea, aim for an acidic pH level of 4.5. Get advice from the cooperative extension agency near you or a reputable nursery concerning the best ways to test soil.

Now it's time to add aluminum sulfate to the soil around a plant that is at least three years old. You can purchase aluminum sulfate at garden stores. Follow the directions exactly and measure carefully. Too much aluminum sulfate can burn the roots of your plant. Fertilizers will aid in keeping the soil at the pH level needed, but most fertilizers contain a mixture of various nutrients and minerals with large amounts of phosphorous and nitrogen. Both elements create fabulously pink hydrangeas, but a desire for blue points us in another direction. Use potash or muriate to fertilize.

If you've done your homework, followed the directions, and added needed elements to the soil, your hydrangea should be ready to begin its chameleon change from pink to blue. A few words of advice, encouragement and just for the fun of it: You won’t wake up the day after adding aluminum sulfate to the soil and find a miraculous change from pink to blue - it takes time. If you let the soil go and stop paying close attention, it will revert back to its alkaline natural state with pink hydrangea blooms dancing on the stems.

Other factors come into play that affect the colors, such as weather, amount of sunlight, and genetics. Even after following all the guidelines and suggestions, you may find that your hydrangea gleams purple in the light of day. An easy solution to the dismay of not being able to produce blue hydrangeas in your garden is to plant them in very large containers where keeping the soil at the perfect pH level is less taxing. Just think of the grand statement a sensational container holding a blue hydrangea will make at the front entry. Now I know why my hydrangeas aren't blue, and you know, too.

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