How To Apply Aluminum Sulfate To Hydrangeas

Aluminum Sulphate To Blue Up Hydrangeas

The Benefits of Aluminum Sulfate for Hydrangeas

Hydrangeas are popular garden plants known for their large, showy blooms. However, the color of these blooms can be affected by the pH level of the soil. If the soil is too alkaline, the blooms will turn pink or red. If the soil is too acidic, the blooms will be blue. Aluminum sulfate is a soil amendment that can help to lower the pH level of the soil, making it more acidic and helping to keep hydrangea blooms blue.

When to Apply Aluminum Sulfate

The best time to apply aluminum sulfate to hydrangeas is in the early spring, before the plants start to bloom. This will give the sulfate time to work its way into the soil and lower the pH level before the blooms start to form. It is important to apply the sulfate at least 2-3 weeks before the expected bloom time.

How to Apply Aluminum Sulfate

To apply aluminum sulfate to hydrangeas, start by watering the plant thoroughly. Then, mix the sulfate with water according to the package instructions. Use a watering can or sprayer to apply the solution to the soil around the base of the plant. Be careful not to get any of the solution on the leaves or blooms, as this can cause damage.

How Much Aluminum Sulfate to Use

The amount of aluminum sulfate to use will depend on the pH level of the soil and the size of the plant. As a general rule, use 1 tablespoon of sulfate per gallon of water for every foot of plant height. So, if your hydrangea is 3 feet tall, you would use 3 tablespoons of sulfate per gallon of water.

Other Tips for Growing Hydrangeas

In addition to using aluminum sulfate, there are other tips that can help to keep your hydrangeas healthy and blooming. Make sure to plant them in well-draining soil, and water them regularly. Hydrangeas also benefit from a layer of mulch around their base to help retain moisture and regulate soil temperature.


While aluminum sulfate can be effective at lowering the pH level of soil for blue hydrangea blooms, it should be used with caution. Overuse of aluminum sulfate can lead to aluminum toxicity in plants, which can cause stunted growth, yellowing leaves, and even death. Always follow the package instructions and use the recommended amount for your specific plant and soil conditions.


By using aluminum sulfate to lower the pH level of soil, you can help to keep your hydrangea blooms blue and vibrant. Make sure to apply the sulfate at the right time, in the right amount, and follow other tips for growing healthy hydrangeas. With proper care, your hydrangeas will continue to delight you with their beautiful blooms year after year.