How to Use Aluminum Sulfate for Plants?

Aluminum sulfate lowers the pH of soils that like acidic plants such as azaleas, camellias, gardenias, hemlocks, hollyhocks, cedars, blueberries, azaleas, dogwoods, and turns hydrangeas blue. Suitable for all soil types, including sandy soils, loamy soils and clay soils. Easy to apply, mix aluminum sulfate into the soil and water thoroughly after application. It also helps turn hydrangeas blue.

When the leaves of your blueberries start to turn yellow or your blue hydrangeas stubbornly bloom pink, it's time to test your soil's pH level. When your soil test results show that your soil is more alkaline than your plants like, lower its pH with aluminum sulfate (also called alum). We recommend using a soil tester prior to application to get accurate soil readings.

Aluminum Sulfate

How do I use aluminum sulfate in my soil?

Measure your garden plot.

Use a tape measure to measure your garden plot so you can get the most accurate results.

Check the soil texture.

Scoop up a handful of moist soil and squeeze it into a ball. Press down on the ball. If it falls apart under light pressure, your soil has a high sand content. If it changes shape and breaks under moderate pressure, it is loess; if it can be shaped without breaking, it is clay.

Calculate the aluminum sulfate needed.

Calculate how much aluminum sulfate you need to apply based on the current pH of your soil, the amount you want to lower the pH to accommodate the plants you want to grow, the size of your garden, and whether your soil has more clay, loam, or sand. In loamy soils, you need 0.6 pounds of aluminum sulfate for every 10 square feet of planting area for the 0.5 pH drop you want to achieve.

If it is a clay soil, add one-half, and if it is a sandy soil, reduce it by one-third. For example, to lower the soil pH from 7.0 to 6.5 for an area of 20 square feet, you would need 1.2 pounds in loamy soils, 1.8 pounds in clay soils, and 0.8 pounds in sandy soils.

Aluminum Sulfate

Measurement and distribution.

For small amounts of aluminum sulfate powder, measure out the amount you need using a measuring cup, and for large areas, calculate from the bag weight on the label. Use gloved hands to distribute it evenly over the soil. A 2-cup measuring cup filled with aluminum sulfate is equivalent to 1 pound. Wash off any powder that comes in contact with plant leaves or grass to avoid injury.

Digging it in.

When preparing garden soil in early spring, use a shovel or rototiller to incorporate aluminum sulfate into the soil about 6 inches. Unlike other pH-altering additives, aluminum sulfate immediately acidifies the soil.

To make a soil drench.

Make a soil drench for established plants (such as hydrangeas) that need a pH reduction by mixing 1/4 cup of aluminum sulfate into 1 gallon of water in a watering can.

Applying a soil drench.

Pour the mixture around the roots of your plants once a week, starting in early spring until they bloom and again in the fall.

For more information and help, please contact us. We have  many types of aluminum sulfate, Boron Trifluoride Diethyl Etherate and other products.