The pH level of your soil plays an enormous role in your plants' health. A measure of its relatively acid or alkaline nature, pH can change with the addition of certain chemicals or elements. Adding limestone to soil is a common practice among gardeners and farmers, helpful for neutralising highly acidic soils.
Types of Limestone
There are many forms of limestone that you can use to change the soil's pH balance. Agricultural lime is simply a finely ground form of limestone rock, available as a powder. Pelletised lime is somewhat easier to work with--the powdered agricultural lime is formed into small pellets, using a water-soluble resin. Because of the extra processing, pelletised lime costs slightly more than agricultural lime. Burnt lime, also known as quick lime, has been heated, increasing its reactivity. Hydrated lime, also known as slaked lime, is a another strengthened form, inappropriate for adding to soils where plants are present; it's formed by adding water to lime and letting them form hydroxides.
Whenever adding limestone to soil, follow all indicated safety precautions on the packaging for the type of lime you're using. Lime can be highly caustic, and it may irritate any exposed skin or eyes. The amount of lime you should add to soil depends on the precise form of lime, because each form has a different amount of calcium carbonate, the active ingredient in limestone. For burnt lime, apply no more than 4.54 Kilogram per 1,000 square feet. For hydrated lime, you can safely apply twice that quantity. If adding ground or pelletised limestone, feel free to add up to 22.7 Kilogram per 1,000 square feet of soil. Keep in mind, too, that the ideal amount of lime to add will also depend on how dramatically you wish to change the pH level.
According to the pH scale, 7.0 is perfectly neutral, neither acidic nor alkaline. However, when neutralising soil, you may wish to make the soil very slightly acidic or slightly alkaline, depending on the plants you plan to grow. For example, blueberries and azaleas both thrive in soil that is slightly acidic. If you grow hydrangeas, changing the soil's pH very slightly can affect the colour of the flowers; neutral or slightly alkaline soil will make the flowers pink, whereas slightly acidic soil will make the flowers blue.
Making Soil Alkaline
If the crops you're planning to grow require alkaline soil, you can use limestone in the same way to increase the pH level of neutral soil. When adding large amounts of limestone to soil, be careful not to overlime. Sandy soils are especially prone to overliming, which can cause deficiencies of nutrients like iron, zinc, manganese, boron or copper.