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Changing Your Hydrangeas’ Color

Hydrangeas are one of the most popular perennials today. One reason may be that the large mop like flowers last a long time without them needing to be deadheaded.
In fact, there is even a cultivar (a plant variety that has been produced in cultivation by selective breeding) called Endless Summer. This is a bigleaf variety, also known as a mophead hydrangea.

Flower color, as well as bloom duration, are also features that endears hydrangeas to people throughout the world. These large flower clusters range from white to purple. The most popular colors, though, are pink and blue. Those two colors are determined by the pH level of the soil.

Many gardeners are fascinated by pink and blue hydrangeas’ ability to change color, even during the growing season. People often ask how that’s done. It sounds complicated but it is simply done by manipulating the soil pH.

If your hydrangea flowers are pink, it means that the soil is alkaline (pH of 7 or above), also known as sour, basic or neutral. If the flowers are blue, it means the soil is acid (pH of 6 or less), or sweet. The best way to turn pink flowers blue is to add aluminum sulfate to the soil. If you want to turn blue flowers pink add lime to the soil. You can buy aluminum sulfate or lime at garden centers. Follow the label directions.

Some common household products can be used in place of aluminum sulfate or lime. Coffee grounds, Epsom salts or vinegar can be used to lower the pH. You probably won’t have to worry about changing blue flowers to pink in the Rochester, NY and Finger Lakes area because most soil is alkaline here.

Changing hydrangea flower color isn’t a party trick in which you place a potion on them, say an incantation and your guests watch the color change before their eyes. It takes awhile; the plant has to absorb the material you put on.

People also ask why their hydrangea flowers turn green. It’s a function of age. Green is the natural color of the sepals. As the sepals age the green color overpowers the pink, blue or white color. Thus the blooms fade to green over time.

When discussing hydrangeas there are two other important points to be aware of. Unlike most flowering shrubs, hydrangeas can be pruned in spring because their flowers grow on new wood while the plants we caution against pruning grow on old wood. The second point is that hydrangeas like partial sun, well drained soil and plenty of moisture.

One comment on “Changing Your Hydrangeas’ Color

  1. In the Santa Clara Valley, they are naturally pink. It takes a bit of effort to get them to bloom blue. If neglected, they revert right back to pink. That is just the nature of the soil. However, in the Santa Cruz Mountains, they are naturally blue in a few areas. It takes a bit of work to get them to bloom pink! At work, we get some to bloom pink, and others to bloom blue. If it were up to me, I would let them all do what they want. The white sort are always white of course.

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