My soil ph is too high

How can I bring it back down to the optimum ph range?


The addition of alkaline materials such as lime, poultry manure or wood ashes to the soil can raise the pH value to levels which are higher than the optimum range (5.8 to 6.5 for most plants) to insure good plant growth. This will occur if excessive a mounts of these materials are added to a soil either all at once or over a long period of time. For plants that thrive best in the pH range of 5.8 to 6.5, soil pH values above 6.5 can cause plant deficiencies of important micronutrients such as zinc and manganese which are still in the soil but “tied-up” and unavailable to the plant.

In addition, blueberries, azaleas, camellias, rhododendron and other acid loving plants require a soil environment more acidic than other plants. In this case, the ideal pH range is 5.0 to 6.0. If the soil is already in the pH range of 5.8 to 6.5, it should be further lowered for the best growth of these plants.

Two materials commonly used for lowering soil pH are aluminum sulfate and sulfur which can be found at any garden supply center. Both materials will do the job. Aluminum sulfate will change the soil pH instantly because the aluminum produces the acid ity as soon as it dissolves in the soil. Sulfur, however, requires some time for the conversion to sulfuric acid with the aid of soil bacteria. The conversion rate of the sulfur is dependent on the fineness of the sulfur, the amount of soil moisture, s oil temperature and the presence of the bacteria. Depending on these soil factors, the conversion rate of sulfur may be very slow and take several months if the conditions are not ideal. For this reason, most people use the aluminum sulfate. Both mater ials should be worked into the soil if possible after application to be most effective. If these materials are in contact with plant leaves as when applied to a lawn, they should be washed off the leaves immediately after application. Be extremely ca reful not to over-apply the aluminum sulfate or the sulfur.

You can use the following tables to calculate the application rates for both the aluminum sulfate and the sulfur. The rates are in pounds per 10 square feet for a loamy soil. Reduce the rate by one-third for sandy soils and increase by one -half for clays.


Pounds of Aluminum Sulfate to Lower the Soil pH
Present pH Desired pH
6.5 6.0 5.5 5.0 4.5
8.0 1.8 2.4 3.3 4.2 4.8
7.5 1.2 2.1 2.7 3.6 4.2
7.0 0.6 1.2 2.1 3.0 3.6
6.5 0.6 1.5 2.4 2.7
6.0 0.6 1.5 2.1
Pounds of Sulfur to Lower the Soil pH
Present pH Desired pH
6.5 6.0 5.5 5.0 4.5
8.0 0.3 0.4 0.5 0.6 0.7
7.5 0.2 0.3 0.4 0.5 0.6
7.0 0.1 0.2 0.3 0.4 0.5
6.5 0.1 0.2 0.3 0.4
6.0 0.1 0.2 0.3


Published: Zarai Media Team

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