How can I get my hydrangeas back to color?

Hydrangeas are prized for their large, colorful blooms that can transform a garden. But sometimes those blooms lose their intensity or even turn an undesirable color. The most common cause of hydrangea color change is soil pH. Blue and purple hydrangeas need acidic soil, while pink and red hydrangeas thrive in neutral to alkaline soil. With a few adjustments, you can get your hydrangeas back to their original, vibrant hues.

What Makes Hydrangea Blooms Change Color?

Hydrangeas contain a naturally occurring pigment called anthocyanin that is responsible for giving the flowers their rich, blue tones. In acidic soils with a pH below 5.5, the anthocyanin pigment is stable and shows blue. But in neutral to alkaline soils, the pigment breaks down and fades, resulting in pink or even red blooms.

Some hydrangea species and cultivars are exceptions. For example, the popular Endless Summer series tolerates a wider pH range. But for most blue hydrangeas, monitoring soil pH is crucial for maintaining the desired flower color.

Other Factors Affecting Hydrangea Color

While soil pH is the main cause of color change, other factors can also influence hydrangea blooms:

  • Insufficient watering can cause fading or browning of blooms
  • Overly wet soil depletes aluminum ions needed for blue color
  • Excess nitrogen fertilizer leads to green rather than blue flowers
  • Cold weather shifts some varieties to pink or purplish tones
  • Insufficient sunlight results in lighter, paler blooms

Paying attention to proper care, including watering, fertilizing, and siting, helps maximize bloom color. But adjusting soil pH is usually the most direct way to restore original hydrangea color.

How to Make Hydrangea Soil More Acidic

Here are some effective ways to lower, or acidify, the pH around blue hydrangeas to intensify their color:

Use Aluminum Sulfate

Applying aluminum sulfate is a quick and easy way to acidify soil. Also called hydrangea colorant, aluminum sulfate provides accessible aluminum ions which intensify blue. Lightly work 1/4 cup into soil around each hydrangea once a month through the growing season.

Incorporate Organic Matter

Mixing in acidic organic materials lowers pH. Peat moss, pine needles, oak leaves, coffee grounds, and sulfur are all useful additions. Work 2-3 inches of organic matter into the top few inches of soil early in the season.

Mulch with Pine, Oak Leaves, or Straw

An acidic mulch helps maintain lower soil pH. Spread 2-3 inches of oak leaves, pine needles, or straw around the base of blue hydrangeas. As the organic matter decomposes, it acidifies the soil.

Use Nitrogen-Fixing Plants

Growing plants like azaleas, camellias, and blueberries near hydrangeas benefits from their nitrogen-fixing roots that leave nitrogen in the soil and lower pH.

Try Chelated Iron

Chelated iron is quickly taken up by hydrangeas and intensifies blue or purple color. Follow label directions and apply around hydrangeas every few weeks during the growing season.

Rule Out Chlorosis

Yellowing leaves with prominent veins, known as chlorosis, is sometimes mistaken for a color change. This is often due to high soil pH preventing iron uptake. Chelated iron corrects chlorosis and restores green foliage.

How to Make Hydrangea Soil More Alkaline

For pink or red hydrangea blooms,aim for a soil pH of 5.5-6.5. Here are some options for raising pH:

Lime and Wood Ash

Adding lime or wood ash makes soil less acidic. Aim for 1/2 cup per plant in spring and repeat after 12 weeks if needed. Wood ash also provides potassium.

Crushed Eggshells and Calcium Carbonate

Other good alkaline sources are eggshells and calcium carbonate, which slowly release calcium. Work 1/4 cup into soil around each hydrangea in early spring.

Bone Meal

Phosphorus-rich bone meal has an alkaline pH. Apply 2-4 tablespoons per plant, mixing into the top few inches of soil in spring.

Seaweed Extract

As a liquid fertilizer, soluble seaweed provides trace nutrients while nudging pH upward. Follow directions and apply every few weeks during the growing season.

When to Adjust Hydrangea Soil pH

Timing acidifying or alkalizing treatments is important:

  • Early spring is ideal before growth begins.
  • Avoid making drastic pH changes during flower development.
  • Amend soil pH gradually over two seasons for best results.
  • Soil tests help determine precise pH needs.

Adjusting soil pH takes time and patience as you gradually nudge it to the ideal range. Test soil pH yearly to determine if further amendments are needed.

How Long Does It Take Hydrangeas to Change Color?

Be patient when attempting to alter hydrangea color. It can take 1-2 seasons to see the full results of soil pH changes. Here’s a general timeline:

  • 1-3 months – minor color changes from fast-acting treatments like iron
  • 3-6 months – foliage responds first as pH is adjusted
  • 12-24 months – significant bloom color change occurs

The process is progressive, with color becoming more intense over time. Persistence and ongoing pH management are necessary to achieve the desired outcome.

How to Confirm Your Hydrangea Soil pH

Testing soil pH annually is advisable to determine acidity levels and additional amendment needs:

Use a Soil Test Kit

Home soil test kits provide a pH reading in minutes. They often contain a color-coded indicator that estimates pH when mixed with a soil sample.

Use pH Meter

A pH meter or electronic tester provides quantitative readings. Simply insert the probe into moistened soil and it displays an accurate pH measurement.

Send a Soil Sample to a Lab

For in-depth data, send a soil sample to a lab like your local cooperative extension. You’ll receive a detailed report on pH and nutrient content.

Observe Visual Cues

Plant growth can indicate pH levels. Blue hydrangeas with reddish stems and yellow foliage likely have alkaline soil, while healthy green leaves signal properly acidic soil.

What is the Best Soil pH for Hydrangeas?

The ideal soil pH for hydrangeas depends on the desired flower color:

Blue hydrangeas – acidic soil with pH below 5.5

Pink or red hydrangeas – neutral to slightly alkaline around 5.5-6.5 pH

White hydrangeas are less affected by pH. Aim for slightly acidic in the 5.5-6 range for whites.

Purples and lavenders thrive in strongly acidic soil around 4.5-5 pH. Monitor soil closely in this range to prevent excess acidity.

Do All Hydrangea Types Change Color Based on pH?

The most pH-sensitive hydrangea species include:

  • Bigleaf hydrangea (Hydrangea macrophylla)
  • Oakleaf hydrangea (Hydrangea quercifolia)
  • Mountain hydrangea (Hydrangea serrata)

Some types are less affected by pH:

  • Smooth hydrangea (Hydrangea arborescens)
  • Panicle hydrangea (Hydrangea paniculata)
  • Climbing hydrangea (Hydrangea anomala subsp.)

Get to know your particular hydrangea’s sensitivity to pH for best color results. Play To Blue and Let’s Dance series, for example, are especially pH-dependent.

Should I Use Aluminum Sulfate on All Hydrangea Types?

Aluminum sulfate only affects certain hydrangea species by intensifying blue hues. It has the most impact on:

  • Bigleaf (H. macrophylla)
  • Mountain (H. serrata)
  • Oakleaf (H. quercifolia)

On hydrangeas that naturally produce pink or white blooms, aluminum sulfate has little benefit. Too much can build up to toxic levels for some plants. Only use it routinely on blue-flowering types that require extra aluminum.

How Often Should I Add Aluminum Sulfate?

During the growing season, adding aluminum sulfate every 2-4 weeks is sufficient for most blue hydrangeas. Use this dosage guideline:

  • 1/4 cup per mature plant
  • 1/8 cup per smaller or young plant

Space applications 2-4 weeks apart. Before the growing season, incorporate 1/2 cup aluminum sulfate into soil around each plant. Test soil pH yearly to determine if more is needed.

Can I Overdose My Hydrangeas with Aluminum Sulfate?

Yes, it’s possible to add too much aluminum sulfate. Avoid over-applying by:

  • Following package dosage rates
  • Spreading it evenly within the drip zone
  • Using the minimum amount needed
  • Testing soil pH to avoid going too acidic

Toxicity symptoms include yellowing leaves with dead patches. Water plants thoroughly to wash away excess if over-applied.


Restoring faded or off-color hydrangeas to their original vibrancy relies heavily on adjusting soil pH. For blue and purple flowers, acidic soil is needed, while pinks and reds require alkaline conditions. With prompt treatment using aluminum sulfate, organic matter, or pH-adjusting amendments, you can successfully change hydrangea bloom colors. Pay close attention to each variety’s pH preferences and make cautious, gradual pH modifications for best results.

Desired Color Soil pH Range Treatment Options
Blue 4.5-5.5 Aluminum sulfate, peat moss, pine needles, coffee grounds
Purple 4.5-5 Aluminum sulfate, sulfur, acidic mulch
Pink 5.5-6.5 Lime, wood ash, eggshells, bone meal
Red 6.0-6.5 Crushed coral, limestone, wood ash

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