Calcium carbonate, more commonly known as calcitic lime or garden lime, has long been a staple in garden, field, and lawn management. Many homeowners make annual applications based on the advice of other growers, professionals, or their own research.
Calcium carbonate is available as a powder or as a granular application. Powdered calcium carbonate works faster in the soil, but is more difficult to apply at a consistent rate. Conversely, pelletized forms are easier to apply, but take longer to break down and provide their benefits.
Feeling like your soil needs a hand? Calcium carbonate is beneficial for correcting several common garden problems, but it should only be used based on the results of soil analysis. It is possible that too much calcium carbonate will make your garden inhospitable for your plants.
Here are five different situations in which you can add calcium carbonate to the garden to improve the performance of your crops.
Correcting Soil pH
Calcium carbonate is an excellent product for raising the pH of soil. Most (not all!) plants do best in soils with a pH between 5.5 and 6.5. Calcium carbonate can be broadcast over and incorporated into soils in need of a dose of alkalinity.
For best and quickest results, it should be incorporated into the soil such as with a tiller, rather than just being allowed to sit on the soil’s surface. This should not just be done as a matter of course though; there are many regions where soils are typically alkaline and calcium carbonate should never be used.
As the name implies, calcium carbonate is a great source of calcium (Ca). Calcium is an important nutrient that strengthens a plant’s cellular walls and is vital in new cell development. A calcium deficiency can lead to common fruit diseases such as blossom-end rot, which is prevalent in tomatoes and peppers.
If a soil analysis determines that a soil is deficient in calcium, but has a pH over 7.0, another source of calcium should be used, such as gypsum, which will not raise the soil pH but still provide the needed Ca.
Reducing Toxicity of Metals in the Soil
One role of calcium carbonate known to many professionals, but that is not necessarily common knowledge to the average home gardener, is its ability to mitigate heavy metals in the soil.
This is usually only a prescribed course of action if a soil analysis indicates that heavy metals are present in the soil at levels that can be remediated; if the levels are too high, removal of the soil would be the likely solution.
Besides being potentially toxic for humans, heavy metals can be toxic to plants as well. Calcium carbonate does not eliminate the metals from the soil, but “ties them up” so that they are not as available for uptake by plants.
Increasing the Efficacy of Other Nutrients
One of the many unseen benefits of using calcium carbonate, as it relates to its ability to adjust soil pH, is its role in making nutrients available to plants.
All of the nutrients that a plant needs may be present in a soil, but they may be unavailable to plants (see Nutrient Lockout) if the pH is not conducive for the plant to easily “grab a hold” of. The majority of nutrients that a plant needs are most available to plants at the aforementioned 5.5 to 6.5 pH range.
Although it's not evident in the name “calcium carbonate”, there is some magnesium (Mg) in this substance. It is sometimes found with or added to calcium carbonate and is a required element for plants. It is more often found in dolomitic lime as opposed to calcitic lime.
Magnesium is required for proper photosynthesis of plants as it is a component of chlorophyll molecules. As such, a plant that is in need of additional Mg will usually show signs of deficiency in its older, lower leaves. They will start to turn yellow between the veins, which will remain green.
In the absence of a site-specific prescription, calcium carbonate is generally applied to gardens and lawns in need of “sweetening” at a rate of one to two pounds (0.45 to 0.9 kg) per 100 square feet (9.3 square meters) of area. In the event of over-application or in soils that have a high pH, sulfur should be applied at the recommended rate.