How to Change Hydrangea Color

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Hydrangeas are a popular flowering shrub in the landscape with showy flowers in late spring through early summer. Hydrangeas provide a large burst of color in the landscape with their large flower clusters. You will often see a variation of color on hydrangeas from blue to pink. It is possible to change the color of some types of hydrangeas based on the soil pH.

There are many types of hydrangeas, but the ones you can change the flower color on are the types usually referred to as mopheads, lacecaps, bigleaf, or French hydrangeas (Hydrangea macrophylla). There are other types of hydrangeas, such as oakleaf (Hydrangea quercifolia) and PeeGees (Hydrangea paniculata) that have white or cream colored flowers which you can not change the flower color of.

The type of hydrangeas you can change the flower color on is determined indirectly by the soil pH. It is actually the availability of aluminum to the plant that determines the flower color but changing the soil pH will dictate whether aluminum is available to the plant or not.

Bigleaf hydrangea (Hydrangea macrophylla) flower color is determined indirectly by the soil pH.

For a hydrangea with blue flowers, the soil pH should be acidic with a pH between 5 and 5.5. The acidic soil allows aluminum to be available to the plant and results in blue flowers. A soil pH of 6 or more will cause aluminum in the soil to not be available to the plant and results in a hydrangea with pink flowers. Many times you see hydrangeas with pink, blue, and purple all on one plant. This is usually because the soil pH is some where’s in the middle (5.5 to 6) so you get flower colors in between blue and pink.

So, if you decided that you want to change the color of your hydrangea you will have to change the soil pH. The first step would be to know what your current soil pH is. The best way to determine this is to get a soil test. Soil test boxes and forms are available at the Wayne County Extension Office. Once you get your soil test results back, you will know what the soil pH is and whether you need to increase or decrease it to get your desired flower color. To increase soil pH, you will need to add lime to the soil. To decrease soil pH, you will need to add sulfur to the soil.

Many soils in North Carolina are acidic (low soil pH), so most people will probably have a hydrangea with blue flowers. Unfortunately, it can take a while for the effects of changing the soil pH to show up in the flower color. Some materials, like lime, will take several months before changing the soil pH. If you have to make dramatic changes in the soil pH to alter the hydrangea’s flower color it can become quite difficult. Even if you do reach the desired soil pH, the soil will naturally revert to its original soil pH. So, it could be a battle to not only change the soil pH but to also maintain that soil pH. If you do change the soil pH, you would want to get a soil test every year or so to monitor changes in the soil pH over time so you would know when you need to apply more material.

Jessica Strickland is an agriculture extension agent, specializing in horticulture for North Carolina Cooperative Extension in Wayne County.

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