Understanding Soil pH and How to Raise It
Soil pH and Plant Growth
The pH of soil, a measure of its acidity or alkalinity, is crucial for plant growth. Most plants thrive in neutral to slightly acidic soils (pH 5.8 to 6.5). However, some plants, such as azaleas, rhododendrons, and blueberries, prefer acidic soils (pH 5.0 to 5.5), while others, like cruciferous vegetables and columbines, can tolerate slightly alkaline soils (pH 7.0 to 8.0).
Soil Acidity and Alkalinity
Soil acidity is not static and can change over time due to natural or human-induced factors, such as excessive rainfall, decomposition of organic matter, and the use of high-nitrogen synthetic fertilizers. Soil acidity below pH 5.0 can hinder plant growth, necessitating measures to increase soil pH.
Testing Soil pH
Before altering soil pH, it is crucial to test it using a pH test kit or meter. This test will determine the current pH level and guide the appropriate soil amendments needed.
Methods to Raise Soil pH
Limestone
Limestone, or garden lime, is the most common soil amendment used to reduce soil acidity. It is ground limestone available in various forms, including pulverized, granular, pelletized, and hydrated. Pulverized lime works fastest but can clog, while granular and pelletized lime clog less. Hydrated lime raises pH quickly but requires careful handling due to its reactivity.
Dolomitic Lime
Dolomitic lime contains both calcium and magnesium, unlike calcitic lime which only contains calcium. Both types of lime neutralize soil acidity equally, but dolomitic lime is often sold in pelletized form.
Timing of Soil pH Amendment
For a vegetable garden, soil should be amended in the fall or winter before spring planting. For established plants, such as hydrangeas, lime can be added in early spring, late spring, or fall. Avoid adding lime during wet summers, as it requires water to react and takes time to change soil pH.
Factors Affecting Soil pH
Rock Type: Acidic granite rock contributes to acidic soil, while alkaline shale or limestone contributes to alkaline soil.
Rainfall: Frequent and heavy rainfall leaches alkaline elements from the soil, making it more acidic.
Organic Matter: Accumulated leaves, pine needles, and other decaying organic matter can also increase soil acidity.
FAQ
Will baking soda raise soil pH?
Baking soda can temporarily raise soil pH, but it is not a recommended long-term solution as it can burn plants.
Which trees prefer high pH?
Redbud and linden trees are among those that tolerate or prefer alkaline soil.
What if I don’t raise the soil pH?
Depending on the severity of soil acidity, plant health may be affected. However, if the soil is not extremely acidic, it may be possible to grow plants that prefer acidic conditions.