The pH measures the acidity or alkalinity of a soil based on a scale from 0 to 14. A neutral pH is equal to 7. Any value above 7 indicates an alkaline soil and any value below 7 indicates an acidic soil. A plant's preferred pH level obviously depends on the type of plant, and is important because it provides insights into how the plant efficiently absorbs nutrients. Understanding how to adjust the pH of your soil requires you to first test your soil to know the current pH value. From here, substances are added to bring the pH value to the desired level.
Steps
Method 1 of 2: Increase the pH
Step 1. Add a source of calcium oxide to make the soil less acidic
The carbonate ion in sources containing calcium oxide corrects and neutralizes acidity.
Step 2. Choose the source of calcium oxide according to the needs of your plant
Some sources of calcium oxide contain micronutrients, such as dolomite, which is a mixture of magnesium and calcium carbonates. Wood ash also provides calcium oxide along with other micronutrients including potassium, phosphate, boron and other elements. Standard calcium oxide is available in 4 different forms of limestone: pulverized, hydrated, in granules and pellets.
Step 3. Apply the calcium oxide source 2 to 3 months before planting (usually in the fall or winter), this way there is enough time for the pH to change
Step 4. Mix the calcium oxide thoroughly into the soil, because most sources of calcium oxide are not very soluble in water
Step 5. Water the soil regularly after adding calcium oxide
The water activates the source of calcium oxide in order to reduce acidity.
Method 2 of 2: Lower the pH
Step 1. Add sulfur or aluminum sulfate to the soil to make it more acidic
Both of these supplements can be found in most garden supply stores.
Step 2. Immediately reduce the pH of the soil by adding aluminum sulfate, which produces instant acidity due to the aluminum content
Step 3. Increase the acidity of the soil slowly by using sulfur
Sulfur is activated in combination with soil moisture, temperature and bacteria to lower the pH of the soil.
Step 4. Combine the sulfur or aluminum sulfate in the soil thoroughly
Step 5. Wash the sulfur or aluminum sulfate off the leaves of the plant they came into contact with to avoid burning the plant
Advice
- Reducing the pH in naturally alkaline or calcareous soils is difficult and sometimes impossible. If this is the case with your soil, plant flowers and shrubs that thrive in alkaline soils.
- When it comes to limestone size, the finer the limestone, the easier it is to absorb into the soil and the faster the pH change.
- Wood ash is not as effective a source of lime oxide as limestone, but its repeated use can greatly raise the pH of the soil.
