How to Add Calcium to Soil: 9 Methods

Nadia Hassani is a a Penn State Master Gardener with nearly 20 years of experience in landscaping, garden design, and vegetable and fruit gardening.

Mary Marlowe Leverette is one of the industry's most highly-regarded housekeeping and fabric care experts, sharing her knowledge on efficient housekeeping, laundry, and textile conservation. She is also a Master Gardener with over 40+ years of experience and 20+ years of writing experience. Mary is also a member of The Spruce Gardening and Plant Care Review Board.

Calcium is one of the secondary macronutrients in soil. While not required in the quantities of nitrogen, phosphorus, and potassium, calcium is crucial for plant growth and makes plants less susceptible to diseases and pests. But when it comes to calcium, more is not always better. Too much calcium in your garden soil can go hand in hand with a high pH, which means the soil is too alkaline. This affects the absorption of the macronutrients contained in other fertilizers.

The way to determine whether you need to add calcium to your soil is through a professional soil test. It is different from a simple pH test that you can do at home. A professional soil test analyses both the calcium level and the pH of your soil. Professional soil tests such as those offered by a state cooperative extension office also will tell you exactly what to add to the soil, and in which amounts.

Keep in mind that in a living plant, calcium moves from the root tips upwards throughout the plant with water via transpiration. That’s why sufficient watering is always important. Once calcium has reached its destination, such as new, young tissue or tips, it will stay put.

How to Measure Calcium in Soil

The calcium level in your soil does not say anything about how much of it can actually get absorbed by plants. Add calcium to your soil when it is low in organic matter and nutrient-absorbing properties like clay, which can be determined by its Cation Exchange Capacity (CEC). This measures the calcium absorption of the soil.

Understanding Calcium Absorption

Imagine the soil like a storage tank of plant nutrients for calcium and magnesium. CEC is the relative ability of the soil to absorb and hold a particular nutrient in the form of cations or positively charged ions. Whether your plants are getting enough calcium—and what you can do about it—is directly connected to the CEC level. It is also linked to the pH of your soil; soils with a higher pH level usually contain more available calcium.

Soil Testing for Absorption

A professional soil test will determine the CEC of your soil. The higher the CEC, the more organic matter and clay are in your soil, which holds water and nutrients better than sandy soil. A low CEC indicates a sandy soil which is more likely to lack nutrients because they leach out of the soil quicker.

Based on the CEC, the soil test might tell you to add organic matter to the soil. It also indicates whether you need to make your soil less acidic by adding lime, or make it more acidic by adding sulfur. The combination of increasing the CEC and adjusting the pH will increase the availability of calcium to your garden crops.

Signs of Calcium Deficiency

While the soil test is the surest way to determine if you need to amend your soil, there are also some telltale signs of calcium deficiency in plants.

Signs of calcium deficiency include stunted or weak growth, curling of young leaves or shoots, scorching or spotting on young leaves, inhibited bud growth, stunted or dead root tips, cupping of mature leaves, chlorosis (yellowing of leaves), burnt leaf tips, and fruit damage such as blossom end rot on tomatoes or bitter pits in apples.

Calcium Fertilizers

There are numerous calcium sources. Which one is right for you, how much to apply, and when depends on the pH level of your garden soil, the timing, and also the crops you are growing.

Lime

Adding lime to your soil is the biggest calcium booster you can give your soil but it also raises your soil pH, making it less acidic. Lime is also known as calcium carbonate and other forms of mined limestone.

Gypsum

This is a fast-acting calcium supplement (calcium sulfate) with low CEC that does not lower nor raise the pH.

Bone Meal

This high-phosphate fertilizer is slower released than lime and less soluble. Use it for soil where you want to moderately raise the pH. Bone meal is especially beneficial for bulbs and root crops.

Egg Shells

For a more effective calcium fertilizer, grind up the eggshells before adding them to the soil. If you do not grind them up, the calcium cannot be released from the shells and into the soil.