How, When, and Why to Add Lime to Your Soil

By James DuckerReviewed by Emily Henderson, B.Sc.

Maintaining soil health is of increasing value in the face of global climate change and growing food insecurity. Supplements including limestone have been used throughout agricultural history but studies are improving our understanding of the mechanisms, benefits, and limitations to lime application, which is key to consider in a rapidly changing world.

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Limestone as a soil supplement to restore soil health

Limestone is made from the calcium deposit of fossilized shells and is readily used as a soil amendment often referred to as garden lime, or lime for short. Most often found as a powdered or pelletized product, lime is a common soil amendment that has been used for thousands of years to increase the soil’s pH to offset soil acidity to improve nutrient availability for plants.  

Using lime therefore can restore the balance of soil acidity and optimize growing levels in otherwise unsuitable conditions for plants. However, despite containing calcium and magnesium, lime does not constitute a substitute for fertilizer as it rebalances soil conditions.

Lime improves soil health, which contributes to plant growth but also overall soil properties. In a 2021 study, Baldovino et al. discussed how lime can also contribute to the strengthening of soil which can facilitate engineering applications including pavement layers and other construction projects. This is due to the fact lime acts as a binder within the soil as it reduces water content and plasticity, which in turn reduces compressibility, swelling, and shrinkage of soil.

Such benefits are highly valued as the spread of urbanized areas is accelerating particularly along coastlines, extending into unfavorable areas that demand stronger soil. However, the use of lime has been associated with air pollution from industrial production and excessive use has resulted in runoff affecting riverine, estuarine, and coastal ecosystems, which have experienced altered water chemistry properties.

Lime application; how, when, and how much lime to add

Plants struggle to grow adequately in acidic soil. Several instances may be indicative of an imbalanced pH including the growth of lawn moss on grass, increased patchiness or erosion, and increased prevalence of pests, pathogens, and weeds.

When such instances occur and other factors are not involved (such as climatic events or transposition of crops), a soil pH test could be used to determine the acidity of the soil. Soil pH can vary across soil type, seasons, region, and surrounding natural features such as waterways or plant communities but generally pH of soil oscillates between 6 and 7. When environmental factors are considered, the addition of limestone in the top 10 to 20 cm of soil can help rebalance pH levels and restore healthy soil.

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The frequency and amount of limestone may vary, but regular pH tests can help determine the overall trend of soil pH above 6. It can take months to restore pH with limestone supplements, but using lime in autumn is often recommended as rain, snow, and freeze/thaw cycles can break down lime faster, but this can vary between regions. Nevertheless, many professional consultants provide services to conduct tests of agricultural or domestic soil areas and provide accurate estimates of the quantity and frequency of lime addition to improve soil health.

Other factors to consider when adding lime to soil

In recent years, studies have elucidated the finer mechanisms of lime application including contextual applications. In a long-term study lasting 24 years, Reihnheimer et al., 2018, demonstrated the temporal dynamics of lime application.

The authors monitored the impacts of surface lime re-application at different rates of soil acidity and its distribution and migration through soil profile in Southern Brazil under a long-term no-tillage (NT) system.

Researchers found that re-acidification of the soil is extremely slow, as only 20% of the original potential acidity was observed in the area after 24 years. Moreover, the changes in acidity were shallower (< 35 cm) than expected, meaning that limestone was unable to penetrate further into the soil.  Authors, therefore, improved our understanding of how lime can change soil chemical properties, and how this effect can depend on the application dose, reaction time, and depth.

The study concluded by advocating for more research on the soil profile of areas treated with limestone, particularly considering the time, rate, form, and application method of lime as well as on cultivation system, soil characteristics, climate conditions, and the addition of acid fertilizer, which will further improve our knowledge of lime usage.

Studies have also considered the limitations of lime application, as the current industry relies on slow curing times that take from weeks to months, and require advances in geotechnical engineering. Further environmental concerns are also affecting the viability of lime application, which often exceeds biologically healthy doses and affects other elements of natural systems.

Addressing emerging issues and improving the sustainable outlook of lime application is of particular importance looking into the future, as urbanized areas are spreading and soil health is decreasing.

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