By Jessica Strickland, Wayne County Horticulture Extension Agent

Popular Shrubs Offer Unique Color-Changing Opportunity

Hydrangeas have long been cherished as one of the most spectacular flowering shrubs in residential landscapes, delivering impressive bursts of color from late spring through early summer. These beloved plants captivate gardeners with their massive flower clusters, but what many don’t realize is that certain varieties offer a rare opportunity to actively change their bloom colors through soil manipulation.

Not All Hydrangeas Are Created Equal

While hydrangeas display a stunning range of colors from vibrant blues to soft pinks, only specific types can have their flower colors altered. The varieties that respond to color manipulation are commonly known as mopheads, lacecaps, bigleaf, or French hydrangeas.

Other popular hydrangea varieties, including oakleaf and PeeGee hydrangeas, produce white or cream-colored flowers that remain fixed in their coloration regardless of soil conditions.

The Science Behind Color Change

The secret to hydrangea color transformation lies not directly in soil pH, but in the availability of aluminum to the plant. Soil pH serves as the controlling factor that determines whether aluminum can be absorbed by the plant’s root system.

Blue Blooms Require Acidic Conditions

For gardeners seeking brilliant blue hydrangea flowers, the soil must maintain an acidic pH between 5.0 and 5.5. These acidic conditions make aluminum readily available to the plant, resulting in the coveted blue coloration.

Pink Flowers Thrive in Alkaline Soil

Conversely, pink hydrangea flowers develop when soil pH reaches 6.0 or higher. At this alkaline level, aluminum becomes unavailable to the plant, producing the pink hues many gardeners prefer.

Purple: The In-Between Color

Many gardeners notice their hydrangeas displaying a mixture of pink, blue, and purple flowers simultaneously on the same plant. This multicolored display typically occurs when soil pH falls in the middle range of 5.5 to 6.0, creating flower colors that blend between the blue and pink extremes.

The Process: Testing and Adjusting Soil pH

Step 1: Know Your Starting Point

Before attempting to change hydrangea colors, gardeners must determine their current soil pH through professional soil testing. Soil test kits and forms are available at the Wayne County Extension Office, located at 3114-B Wayne Memorial Drive in Goldsboro.

Step 2: Adjust pH Accordingly

Once soil test results are obtained, gardeners can take appropriate action:

• To increase pH (for pink flowers): Add lime to the soil
• To decrease pH (for blue flowers): Add sulfur to the soil

Challenges and Realistic Expectations

Regional Soil Considerations

Most North Carolina soils naturally tend toward acidity, meaning many gardeners likely already have blue-flowering hydrangeas without intervention.

Time and Persistence Required

Changing hydrangea colors requires significant patience. Soil amendments like lime can take several months to alter pH levels effectively. Dramatic pH changes needed for color alteration can prove particularly challenging to achieve and maintain.

Natural Reversion

Even after successfully changing soil pH, the earth naturally reverts to its original pH level over time. This means gardeners must commit to ongoing maintenance, including annual soil testing and regular amendment applications to preserve their desired flower colors.

Safety Considerations

Experts caution against making rapid pH changes, which can cause foliage browning and stress the plant.

A Unique Garden Experiment

According to Strickland, bigleaf hydrangeas represent the only common landscape plant that allows gardeners to manipulate flower color through soil chemistry. With proper knowledge of soil pH principles and adequate patience, these plants can serve as fascinating science experiments in home gardens.

Expert Resources

Jessica Strickland serves as an Agriculture Extension Agent specializing in horticulture for North Carolina Cooperative Extension in Wayne County.

Additional Information

Gardeners seeking more information can access several resources:

• Wayne County Extension Gardening email list for timely tips: https://wayne.ces.ncsu.edu/email-me
• Social media updates: Facebook @waynecooperativeextension and Instagram @waynecountyextension
• North Carolina Extension Gardener Plant Toolbox: https://plants.ces.ncsu.edu

For more gardening advice and horticultural guidance, contact the Wayne County Extension Office.