Amendments to Make Soil Alkaline
- Soil's alkalinity can dramatically affect a plant's growth.Michael Hitoshi/Photodisc/Getty Images
PH level is an important property of soil composition. Commonly known as "acidity," it actually refers to the relative acidity or alkalinity of a soil sample. Soil with a pH level below 7 is considered acidic; pH levels above 7 are alkaline. If your soil is too acidic for your plants, you can increase its alkalinity by adding one of several additives. Keep in mind that changing soil's pH can be a long, gradual process. - One of the most popular means of making soil more alkaline is by adding lime, a carbon-rich organic material commonly found in limestone. A popular and fairly foolproof way of adding lime to soil is in the form of ground limestone. Alternately, you can add hydrated lime; however, hydrated lime poses a greater risk of over-liming the soil, making it excessively alkaline. The amount of lime necessary will depend on the soil's consistency, whether sand, loam or clay. For example, if your soil is sandy loam and has a pH of 5.0, you'll need to add 8 pounds of ground limestone to every 100 square feet of soil to raise the pH level to 6.5. If the same soil has a loamy texture, you'll need to add slightly more lime, around 10 pounds. For clay soil, you'll have to add even more: 15 pounds per 100 square feet.
- Wood ash also effectively increases a soil's pH level, making it more alkaline. As with any soil amendment, it's important to carefully monitor your soil's pH prior to adding wood ash, as too high a concentration of wood ash can make the soil toxic. However, if you do have markedly acidic soil and you wish to neutralize it, adding wood ash will offer several secondary benefits. Adding it to soil can repel common pests such as insects, slugs and snails. When applying wood ash, handle it as you would alkaline bleach, with eye and skin protection and possibly a dust mask. Also, only use wood ash from clean wood fires. Do not use the ash from painted or treated wood, which may contain toxic chemicals.
- An unusual but efficient method of increasing soil alkalinity is to add ground oyster shells or other shells containing high levels of calcium carbonate. If you have access to a supply of ground shells, they make a convenient, organic and completely safe additive to soils. Nonetheless, as with any soil amendment, carefully measure the pH level of your garden's soil before adding the shells to avoid making it too alkaline. According to Monroe Rasnake and Lloyd Murdock's work on Liming Acid Soils, from the University of Kentucky's Department of Agronomy, ground oyster shells have a "relative neutralizing value" of 90 to 95, compared with agricultural limestone's widely varying values of 50 to 100, or ground lime's range of 80 to 100.
