Changing Hydrangea Color

Hydrangea Elizabeth Ashley

Hydrangeas are beloved by gardeners--especially those of us that adore the combination of chemistry and botany--for their color-changing capabilities. If you're looking for a way to add some colorful variety to your garden, plant the hydrangea varieties that change their coloring based upon soil pH.

Hydrangea Color Change: Pink or Blue, It's Up to You

Hydrangea bloom color is determined by the aluminum availability in the soil Generally, most soils contain aluminum but the PH determines whether this nutrient is available for the plant to "take up" the aluminum through the roots. Acidic soils allow the aluminum to be soluble, which is the ability for the aluminum to dissolve and create a solution which is then absorbed by the roots. Alkaline soils inhibit this process by making aluminum insoluble and therefore unable to dissolve and create the solution needed for the blue pigment to be expressed.

A few things to note: Hydrangea blooms will only change color if they start as either blue, pink, or purple. All PH and aluminum dependent color-changing hydrangea varieties belong to the macrophylla or serrata groups. Also, please note, not all macrophylla and serrata varieties will change color. Green hydrangea blooms, most whites and some reds are static and will not change color. The color-change with a few white flowering varieties only occurs in the center of each individual flower. Sometimes there will be a light cast on the petals of these varieties. Regardless of the way you choose to grow them, your hydrangeas are sure to brighten your garden- whether in pink, blue, purple, white, red, green, or somewhere in between.

If you want to know how to change the color of your hydrangea, read on for tips on how to make that magic happen.

How to Turn Your Hydrangeas Blue or Purple:

In order to turn, or keep your hydrangea blue, aluminum is required. Aluminum is an element found in most soils. To make sure this vital element is present in your soil and to make it available to your hydrangea follow these key steps to success:

hydrangeas blue or purple
  • Test your soil before applying any chemicals to your plant. For blue hydrangeas, you want to establish an acidic soil. As mentioned above, acidic soils allow the hydrangeas to absorb aluminum. Aim for a pH between 5 and 6.
  • If you need to lower your soil pH, add fertilizer rich in potassium, or a commercial soil acidifier. These products, usually supplied with clear instructions, are available at most garden centers and hardware stores.
  • Aluminum sulfate, added throughout the season, can aid in keeping the cycle going if your soil is deficient in aluminum. Be sure to follow the instructions on any aluminum sulfate products you've purchased.

Note that some plants won't turn all the way to blue, but will shift to a lovely lavender or purple color when planted in acidic soil with aluminum.

How to Turn Your Hydrangeas Pink:

Pink-colored flowers occur when the plants are growing in alkaline soil, as the pH of this soil will keep hydrangeas from absorbing aluminum and expressing the blue or purple color pigment. To get pink hydrangeas, you should:

hydrangeas pink
  • Test your soil before applying any chemicals to the plant.
  • Keep your pH level above 6.5.
  • Use a fertilizer with higher levels of phosphorus as the planting season progresses.
  • Consider keeping your hydrangeas in containers, especially if you live in an area with naturally acidic soil.

Note that not every plant will turn fully pink, and may land in the purple zone. This is variety dependent coloring, and hydrangeas are sure to be lovely in any shade. If you're ready to get started growing these beautiful blooms in your garden, Spring Hill is here to help. Learn how to plant hydrangea and how to prune hydrangea plants.

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