Change the Color of Your Hydrangeas: A Gardener’s Guide for Zone 8A

One of the most magical things about hydrangeas is their ability to change color depending on your soil's chemistry. If you’ve ever wished your pink hydrangeas were blue—or vice versa—you’re in luck. With a little patience and the right materials, you can influence your blooms in time for the next growing season.

Here’s how it works, what you’ll need, and when to start if you’re gardening here in Zone 8a (Aiken, SC).

Understanding the Science Behind Hydrangea Color

Hydrangea macrophylla—the classic bigleaf or mophead hydrangea—is the species that responds to soil chemistry. The color shift is all about pH and aluminum availability:

• Blue flowers appear in acidic soil (pH 5.0–5.5) where aluminum is available to the plant.

• Pink flowers appear in alkaline soil (pH 6.0–6.5) where aluminum is tied up and unavailable to the roots.
  

  Aluminum is key to turning flowers blue, but the soil must be acidic for the plant to absorb it.
  Phosphorus can block aluminum uptake, so low-phosphorus fertilizers are preferred for blue hues.

When to Start in Aiken (Zone 8a)

To enjoy color-changed blooms next summer, begin adjusting your soil in fall or early winter—ideally October through January. This gives amendments time to adjust the soil chemistry before the plant begins active growth in early spring.

How to Turn Your Hydrangeas Blue

Goal: Lower the pH and make aluminum available.

1. Soil Test First
   Use a soil test kit to determine your current pH. You’ll want it between 5.0 and 5.5 for blue blooms.
   

2. Apply Aluminum Sulfate

• Begin in October.

• Mix 1 tablespoon of aluminum sulfate per gallon of water.

• Apply around the base of the plant, keeping it away from the stems.

• Repeat once per month through March.
  

3. Choose the Right Fertilizer
   Use a low-phosphorus fertilizer like 25-5-30. The middle number (phosphorus) should be low to avoid blocking aluminum uptake.
   

4. Mulch With Pine Needles or Oak Leaves
   These naturally acidify the soil and help maintain a lower pH.

How to Turn Your Hydrangeas Pink

Goal: Raise the pH and limit aluminum availability.

1. Soil Test First
   Aim for a pH of 6.0 to 6.5.

2. Apply Garden Lime

• Begin in October.

• Use 1/2 cup of dolomitic lime per 10 square feet, lightly worked into the soil around the base.

• Repeat every 2–3 months through March, checking pH periodically.
  

3. Choose the Right Fertilizer
   Use a balanced or high-phosphorus fertilizer such as 10-20-10 to block aluminum uptake and support pink tones.
   

4. Avoid Aluminum
   If your soil is naturally high in aluminum, container planting may be a better option for full control.

Be Patient – Color Change Takes Time!

Hydrangea color doesn’t change overnight. It can take a full season—or sometimes longer—for soil amendments to influence bloom color. The sooner you start, the better your results next year.

A Final Note

Keep in mind that white hydrangeas (like ‘Annabelle’) do not change color based on soil pH—they will always stay white.

If you're unsure of your current soil makeup or want a more precise approach, stop by Cold Creek Nurseries—we have soil testing kits, the right soil amendments, and knowledgeable staff to help you create your dream garden bed.

Ready to try a little garden magic? Fall is the time to begin. Let’s get those hydrangeas blooming just the way you want them next summer.