Calcium is one of the most abundant elements on Earth, and most soils in the US have a good amount of it. All plants need calcium for strong cells and firm roots, stems, and leaves. It’s hard to give your lawn too much calcium, but if calcium levels on a soil analysis are too high, it might mean the soil is deficient in something else.
High calcium content will have an impact your soil’s pH, which affects whether certain nutrients are available to the grass. You can amend the soil with compost, acidifying organic materials, or mineral concentrates to adjust the pH and calcium content to the healthiest conditions for your lawn.
Why Do Plants Need Calcium?
Since plants don’t have bones, their roots, stems, and leaves have to be their own support, so they need to be firm. Calcium provides that structure in plant cells, which allows plants to stand upright with extended, flat leaves. Leaves that are wilted or curled can’t absorb light as efficiently as those with a more rigid surface area. Strong plant cells and tissue also provide some resistance against pests and disease.
Soil Nutrient Profile
Since calcium provides structure and support for overall cell health, it’s an essential nutrient. Luckily, many regions in the US have soil that is abundant in calcium. In the event of a calcium deficiency, it may be due to one of a few causes:
- Runoff from erosion or rain
- Drained below root zone
- Absorbed and depleted by grass
If you get a soil profile test back, it will list the amounts of each nutrient in the soil, including the main macronutrients (NPK: nitrogen, phosphorus, and potassium), and micronutrients like iron, magnesium, and copper. Calcium is a secondary macronutrient and isn’t needed in as large amounts as the main NPK macros.
What Causes High Calcium Levels In Soil?
Calcium occurs naturally in the earth’s bedrock, which slowly breaks down over time and contributes minerals and coarse material to the topsoil. In areas that have a limestone bedrock, soils are particularly rich in calcium. Other areas may have less calcium in their soil, which would require amendments to make the ground hospitable to grass.
If too much calcium is added to the lawn, or too many other nutrients are depleted, the calcium ratio in your yard can rise higher than it needs to be. High calcium levels mean a deficiency in other nutrients, whether it’s due to the relative calcium ratios, or whether the excess calcium is affecting the soil’s pH and making other nutrients unavailable.
Soil pH And Calcium
Calcium is a dynamic mineral that affects any given soil type in various ways. Some sources of calcium raise the pH level, and others can lower it. The pH level determines whether certain nutrients can be absorbed, so balanced calcium levels are important.
Calcium itself has the smallest window of availability, between 6.5 and 7.5. Since most grass types like a slightly acidic 6.5-5.5, too much calcium may raise the pH above 7, at which level many nutrients, like iron, copper, and zinc, bind to solids in the soil and become unavailable to be absorbed by roots.
Sources Of Calcium
You can adjust your lawn’s calcium levels by adding:
When a yard is deficient in calcium, or the soil is too acidic, lime can be added to increase the mineral content and raise the pH. In this situation, if too much lime is applied, the yard can become too alkaline. A high pH locks up nutrients, especially iron, copper, and zinc, all of which are essential to a plant’s good health.
Adding too much lime at once is also inefficient. Calcium is used by your lawn throughout the year (except, of course, when it’s dormant), but the ground limestone can be rinsed away in just a few months. Applying too much at once may result in most of it being rinsed away before it’s able to be used. An even, spaced out application of lime is better than too much at once.
Gypsum is another mineral source of calcium. Whereas lime (calcium carbonate) is alkaline and raises soil pH, gypsum (calcium sulfate) is pH neutral and can add calcium to your soil without lowering the acidity of the ground.
Calcium is abundant in organic material, including fruit, vegetables, egg shells, leaves, grass, and other materials that go into your compost. Adding compost to your lawn increases the acidity and can balance out an over-alkalized lawn from a lime application, or bulk up the soil as organic material depletes.
When organic material is broken down, whether in your yard or in a compost pile, the minerals that make up the material get broken down as they decompose. Worm castings are especially high in calcium.
What Does Calcium Do To Soil Structure?
In addition to affecting the pH and nutrient availability, calcium has an effect on the structure of the soil. Gypsum, like lime and compost, adds solid material to the soil that increases the structure and porosity. The chemical nature of calcium increases the porosity as well and is particularly used in clay soils to break up the clay’s dense form.
On the other hand, sandy soils, which drain moisture, tend to be more alkaline in dry areas and may not need the pH to be raised. Well-drained ground may retain even less water if too much calcium is added, in addition to increasing the likelihood of alkaline soils.
Like with any fertilizer, it’s important to do a soil test before trying to adjust the pH or nutrient levels. Even organic materials can be over-applied, as can be the case with lime. A soil test will help you confirm whether or not something needs to be applied: the problem might not be a lack of nutrients, but the wrong pH level, and this is frequently true for calcium.
Soil Base Saturation
In the event your soil does have too much calcium, it may be from an over application of a calcium-rich fertilizer, or from a deficiency of other minerals. A professional soil analysis will include a set of metrics called the base saturation, showing calcium, hydrogen, sodium, magnesium, and potassium.
Calcium is usually between 65-75% of this makeup, but if it’s higher than that, one or more of the other nutrients in the group should be amended to adjust the ratio.
How Do I Reduce Calcium Levels In My Lawn?
Lowering calcium level is more difficult than raising it, but with the right additives and some time, the soil’s levels can adjust to give your grass the most supportive growing environment. You can do this by lowering the pH or by adding organic material.
Calcium becomes less available below a pH level of 6.5, and most grasses like slightly acidic soils that measure down to 5.5. This gives you a little room to increase acidity and lock up some of the available calcium. As long as you don’t make the yard too acidic, this won’t deprive your grass of the calcium it needs. Peat moss, elemental sulfur, or iron sulfate can be added to the topsoil to acidify the soil.
Adding fresh compost to your yard, whether plant compost or worm castings, will dilute the calcium levels by adding bulk to the soil while acidifying over time as the material continues to decompose. Any materials being added to the topsoil to reduce calcium levels should be mixed in well, either by tilling or aerating, depending on the extent of the need, then topdressing.