How to Change Hydrangea Color: Blue or Pink by Soil pH

More on hydrangeas

• Hydrangea planting zones — every type, the zones it suits, and when the last spring freeze lands in each zone
• Why Is My Hydrangea Not Blooming? Causes and Fixes
• How to Prune Hydrangeas by Type: Old Wood vs New Wood
• How to Change Hydrangea Color: Blue or Pink by Soil pH — this page
• How to Prune Limelight Hydrangea and Vanilla Strawberry
• How to Prune Annabelle and Incrediball Hydrangeas
• How to Prune Endless Summer Hydrangeas (Rebloomers)
• How to Prune Oakleaf Hydrangea: After It Flowers
• Hydrangea Pruning Chart: When to Prune Each Type
• Hydrangea Tree Care and Pruning (Tree-Form Panicle)
• Hydrangea Winter Care: Fall Pruning, Cages and Mulch
• ZIP code zone finder — your exact USDA zone, to read the tables on these pages against

Which hydrangeas can change color

Some hydrangeas change color as they age, which is not the same thing. Oregon State says panicle hydrangea flowers gradually turn shades of pink as they age, and Penn State says oakleaf hydrangea’s white flowers mature to shades of pink.

How it works: pH and aluminum

Ohio State: at lower pH (acid soils) aluminum is more readily available to the plant and the flowers turn blue; at higher pH (more alkaline soils) aluminum is less available and they are pink. Penn State says Pennsylvania soils have plenty of aluminum, so the job there is lowering the pH far enough for the plant to reach it.

Phosphorus is the other half. Oregon State says phosphate limits the plant’s ability to absorb aluminum, and Ohio State says high phosphorus at low pH ties aluminum up as aluminum phosphate, which the plant cannot use. That is why the sources say low-phosphorus fertilizer for blue and high-phosphorus for pink.

The pH for each color, by source

The four sources do not agree to the decimal, so each is shown as it published, not averaged.

Test the soil first

Ohio State says have the soil tested by a soil lab, for an accurate pH and a recommendation for the right amount of lime or sulfur for the color you want. Its warning is plain: There is no absolute recommendation for an amount of sulfur or lime to change soil pH without a valid soil test for the garden site. Recipes on websites and in publications, it says, are not accurate for specific soils.

• Ask for aluminum and phosphorus too. Ohio State says a standard test reports phosphorus, and an aluminum test usually costs extra but is needed if you plan on blue flowers.
• Test every year if you want a consistent color (Ohio State).
• Test before planting. Oregon State says if color matters, test before you plant, because adjusting pH is easiest then.

To make flowers blue

• Lower the pH with sulfur. Penn State: elemental sulfur or a soil acidifier. Oregon State: garden sulfur.
• Avoid high-phosphorus fertilizer. Penn State, and Oregon State: use a fertilizer low in phosphate.
• Be wary of aluminum sulfate in the garden. Penn State says commercial growers use it in soilless potting media, that adding it is unnecessary in Pennsylvania soil and that it may damage hydrangea roots. Oregon State’s 2024 article suggests it only for potted plants in soilless mix; its older care page lists it for established plants only.

To make flowers pink

• Raise the pH with lime. Penn State and Oregon State. Oregon State’s care page also names superphosphate.
• Use a fertilizer high in phosphorus, which keeps aluminum out of the plant (Penn State).

How long it takes

• Penn State: it may take more than a year to see a change.
• Oregon State: amendments are best added in fall, and color changes may take several years.
• Ohio State: raising pH takes longer than lowering it, so you may wait a year to see blue turn pink — and even after lowering the pH, some flowers may not turn blue within a year where the soil is high in phosphorus or low in aluminum.

Where blue is hard or impossible

• Next to concrete. Penn State says lime may leach from house foundations and sidewalks, and there blue flowers may be difficult or impossible.
• Alkaline soil and water. Oregon State says bluing bigleaf types is difficult in alkaline soils, and that high-alkalinity irrigation water can raise soil pH. It notes western Oregon soils are often acidic enough for blue, and still says test before bluing.
• The wrong type. Smooth, panicle, oakleaf, climbing and white bigleaf hydrangeas will not turn blue whatever the soil (table above).

Common mistakes

• Amending without a soil test. Ohio State says only a soil-test recommendation can be trusted.
• Trying to turn a white, smooth or panicle hydrangea blue. Their color does not follow pH (Penn State, UF/IFAS).
• Adding aluminum sulfate to garden soil that already has aluminum. Penn State says it may damage roots.
• Feeding a blue hydrangea a high-phosphorus fertilizer. Phosphorus locks up the aluminum (Ohio State, Oregon State).
• Expecting a change the same season. Penn State, Oregon State and Ohio State all talk in years, not weeks.
• Planting a blue hydrangea against a foundation. Lime leaching from concrete works against it (Penn State).

In the South

UF/IFAS says soil pH does not change the color of panicle hydrangeas, and that French (bigleaf) hydrangeas do best in North and Central Florida with shade, moist fertile soils and cool winters. We found no Texas source on hydrangeas, so Texas advice here is limited; ask your county AgriLife Extension office.