How do I change my hydrangea's flower color?
Written by
Michael Sullivan
Reviewed by
Prof. Martin Thorne, Ph.D.To alter the flower colors in hydrangeas, especially for bigleaf and mountain hydrangeas, it involves precise adjustments in soil chemistry. These special plants can produce anthocyanin pigments, which can be influenced by aluminum availability, resulting from changes in soil pH levels. The process requires time and close monitoring, but the results can be spectacular. For instance, I transformed the flower color of my Nikko Blue hydrangea from bright pink to blue, and it returned to pink the following season.
Blue Blooms Method
- Lower soil pH to 5.2-5.5 using aluminum sulfate applications
- Apply 1 tablespoon per gallon of water monthly during growing season
- Maintain acidic conditions to increase aluminum availability for plants
Pink Blooms Method
- Raise soil pH to 6.0-6.2 using dolomitic lime applications
- Spread 1 cup of lime per plant quarterly around the drip line
- Reduce aluminum uptake by creating alkaline soil conditions
Timeline & Maintenance
- Begin adjustments in early spring before bud formation starts
- Test soil pH every 4-6 weeks using reliable testing kits
- Expect color changes to appear gradually over 2-3 blooming cycles
Natural Limitations
- White hydrangea varieties remain unaffected by pH changes
- Soil with high phosphorus levels blocks aluminum absorption
- Extreme pH levels below 5.0 or above 7.0 harm plant health
Soil preparation should take place before any efforts to change color. First, test the existing pH, adding amendments only after reliable testing kits have been employed. Next, mulch should be removed from the root zone during applications to ensure mineral contact with plant roots. Following the addition of each product, water the soil thoroughly to allow minerals to move throughout. Finally, avoid using fertilizers that would interfere with the effectiveness of each treatment.
"Natural options" are coffee grounds, which can provide some degree of acidity, but work slowly. Wood ash can provide moderate pH increases, but it contains varying mineral compositions. Commercial options, such as aluminum sulfate or dolomitic lime, can consistently shift the color of the soil because they alter its pH. Organic materials are always combined with the minerals that I use specifically for soils high in carbon.
Maintain the color stability of hydrangeas by performing pH testing every 3 months and applying light maintenance treatments. To preserve acidity for blue blooms, mulch intensively with pine needles or oak leaves. To maintain alkalinity for pink hydrangeas, apply a layer of limestone gravel loosely around the plants. Remember that watering consistently is important; drought stress can alter the concentration and availability of the mineral nutrients in the soil.
Some types have color change limits. Panicle oakleaf and smooth hydrangeas will not change colors regardless of soil pH levels. The white varieties turn shades of pink or blue only at the bud stage before opening. Additionally, container plants will exhibit color changes more quickly than plants in the ground because the soil environment is more controlled.
Read the full article: How to Care for Hydrangea: Complete Growing Guide
