How to Sustainably Reduce Soil Acidity


By Emily Folk

The plants we grow are just as dependent on nutrition as we are. If their soil is too acidic, too basic, or doesn’t contain the right nutrients, they just won’t grow. Some like the soil to be toward the acidic side of the pH scale, while others prefer their soil to be more base. If your local soil is too acidic or has a pH that is wrong for the types of plants you want to grow, what can you do to sustainably lower the soil acidity?

High soil acidity can cause a host of problems.

Why does soil that is too acidic cause problems for plants?  For starters, extremely acidic soil can burn the roots of the plants which makes it impossible for them to leach the nutrients they need from the soil. Eventually, this will kill the plant altogether. Acidic soil can also lead to plant toxicity. While elements like aluminum, zinc, iron and manganese are all necessary for plant growth, in higher amounts they can damage or kill plants.

Acidic soil also makes it harder for plants to access other essential macronutrients like phosphorous. In an acidic environment, phosphorous bonds to iron and other metals, creating oxides that are useless for plant growth. Acidity can also make it impossible for  plants to absorb other vital nutrients such as magnesium, potassium and calcium.

Finally, soil that is too acidic reduces microbial activity. Microbes that help to do things like add nitrogen to the soil cannot survive in acidic environments.

You can lower acidity with agricultural limestone.

There are two primary types of limestone used in agriculture dolomitic lime, which is magnesium based, and calcitic lime, which is calcium based. While applying magnesium or calcium alone will not lower the soil’s PH the lime, which comes in carbonate, hydroxide, silicate or oxide forms, can be applied to slowly lower the PH levels of the soil.

Introducing agricultural limestone into a field creates a neutral soil that allows the planted crops to absorb more of the nutrients that they need to thrive.

While limestone does occur in nature, mining it hasn’t always been the most sustainable option for the agricultural industry. Instead, farmers have started reclaiming manufacturing waste, repurposing materials that would otherwise be discarded and using them in the agricultural industry.

Wood ash has been used for centuries to control pH.

Wood ash  is actually considered a waste product, because it is produced by burning wood, but it is still one of the best tools for reducing soil acidity in the world. Wood ash is high in calcium, which is almost as good as agricultural limestone when it comes to de-acidifying soil.

The biggest benefit to using wood ash over other types of soil treatments is that it is so potent. You only need to treat your field with wood ash once every two to three years.  Any more than that and you risk reducing the acidity to the point where the soil becomes base, which can be detrimental to your crops.

Wood ash does need to be applied early—it’s recommended to sow your fields with ash in the autumn before the spring planting season to give it time to work and to dissipate enough that it won’t harm the roots of your new plants.

Oyster shells are another sustainable option.

In some parts of the country, oyster shells are useful for reducing the acidity of soil. Composted oyster shell is in many cases more effective than fresh alternatives, but both can be used in the same context.

Oyster shells are among the most sustainable soil treatments on the planet. Oyster farming is an incredibly sustainable field, because they can be grown in huge numbers without having to introduce things like antibiotics into the water supply. They are filter feeders and often leave their farm areas cleaner than when they were seeded!

No matter what you choose to use, the pH of your soil is important.  Take the time to have it tested before you plant anything this season.

Emily is a sustainability writer and avid gardener. You can read more of her work on her site, Conservation Folks, where she writes about helping tomorrow’s planet today.