How to Add Calcium to Your Soil for Healthy, Pest-Resistant Plants

When tending to your garden, it's important to ensure that your soil is rich in nutrients. One of the key factors is calcium—the right amount can help your plants grow healthy and strong. Knowing how to amend your soil and add calcium is essential, then, to a thriving garden.

For beginner gardeners, adding nutrients to the soil may sound like a daunting task. Fortunately, with the right know-how, the process is easy to understand and perform. Here's how the experts say to do it.

Benefits of Calcium

The right amount of calcium in the soil can be extremely beneficial for your plants. "Nitrogen, phosphorous, and potassium are the most important [nutrients]," says Juliet Howe, founder of Twigs Design. "Calcium [also] plays a pivotal role in your garden's well-being."

She notes that calcium is a "fundamental building block for plants developing strong cell walls," which is essential for growth. For plants to grow strong and upright, supporting leaves, fruit, and flowers, they require healthy cell walls.

Calcium can also help your plants better fight against pests and other common issues. "By activating enzymes, or signaling a stress response, calcium kicks off metabolic systems within the plant," she adds. "Then, by binding to proteins within the plant's cells, it helps the plant protect itself."

There are even structural benefits that it can apply to the soil. "[It] essentially creates larger clumps, creating larger pores, which enhance aeration and drainage," says Damon Abdi, assistant professor of landscape horticulture at Louisiana State University.

Warning

Calcium can be great for your plants, but only if it's used in moderation. Applying this nutrient to the soil when it doesn't need it can lead to calcium shock. This can lower the soil pH, says Howe, and affect your plant's ability to take in other nutrients.

"This can lead to stunted plant growth, yellowing leaves, and fewer or damaged fruit and flowers," she says. Always test the soil before adding calcium, so you know exactly how much to add (if any).

Types of Calcium

There are many different ways to administer calcium—the one you choose will ultimately determine how and when you apply it. Experts recommend the following:

• Gypsum: Howe recommends gypsum for clay soils and soils high in sodium. It can also make the soil more capable of absorbing air and water. It's a rapid-release solution, so the calcium will be applied quickly.
• Eggshells: It's possible to compost organic material that you already have at home, transforming it into a calcium source. Eggshells are a great example—just make sure to grind them up beforehand, as this will help the soil absorb the nutrients more quickly. Howe also recommends oyster shells—bear in mind that these methods will be more organic and sustainable, but will also apply the calcium much more slowly, so they're certainly not a quick fix.
• Lime: Agricultural lime can raise the pH of your soil and infuse it with beneficial calcium. It's a slower-release product, but it works well. If your garden needs calcium and magnesium, then Howe recommends using dolomite lime.
• Bonemeal: Bonemeal won't change the pH of your soil, and provides nitrogen and calcium. "It’s especially helpful in preventing blossom end rot in tomatoes," adds Howe.

How to Do It

Ready to get started? Before you do, always test the soil. This will let you know the pH of your soil and its nutrient content—this info will help prevent over-fertilizing. You can send a soil sample to a local Cooperative Extension service, or purchase a DIY kit and test it yourself.

Once that's done, here's how—and when—to apply calcium properly, depending on the medium.

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Gypsum

Gypsum won't alter the pH of your soil; Howe recommends applying it when the pH level is between 6.2 and 7.5. Apply it in the spring, several weeks before planting anything.

"Spread the gypsum granules evenly over the surface, or dig into the top layer of soil," she says. "Water very well so the granules infiltrate the soil, reaching the root system."

Eggshells

Make sure to wash eggshells thoroughly so they don't attract pests, and grind them into a fine powder. Do a soil test in the early spring and apply the eggshells in the fall.

Lime

Lime can be applied in the fall if your soil has a pH of less than 6, according to Howe. "Spread [it] evenly over the entire garden area, and dig into the soil," she says. "Water well after spreading and mixing the lime to help it react and move through the soil."

Bonemeal

Bonemeal also provides phosphorous, so Howe recommends using it in soil with a pH of 7 or lower. Apply it in the spring at the beginning of the growing season.

It can be dug into the soil when you're planting, or used as a top dressing around the plants, that's then scratched into the soil. Make sure to water very well so that it breaks down.