How to Know if Your Plants Need Calcium—Plus, 5 Ways to Add It Naturally

If you have a garden, you should know (if you don't already!) that calcium is a vital nutrient that enables your plants to grow healthy and strong. Calcium strengthens the cell walls of plants, promoting growth and resilience from diseases and pests. Adding calcium to your plants can help your garden thrive. In this guide, plant experts weigh in with their insights on when and how to add calcium to your plants for a lush outdoor environment. 

Why Do Plants Need Calcium?

Calcium is an essential nutrient for plant growth and maintenance. It is a building block for plant cell walls, giving plants structure and rigidity. Calcium also acts as a signaling molecule, regulating cellular growth, development, and stress responses.

“Calcium leads to a stronger cell wall structure, which offers plants a degree of resilience to tough weather and pests,” says Matthew Wilson, horticulturist and CEO of Handy Gardeners. “This improves general plant resilience.”

Signs of Calcium Deficiency in Plants

Calcium deficiency can occur in plants when there is not enough calcium in the soil or the transport of calcium to the plant is interrupted by conditions such as irregular watering or high heat and humidity.

Symptoms of calcium deficiency include stunted plant growth, leaf curling, dark leaf veins, weakened plants, and blossom-end rot in fruits. Fruit plants like tomatoes and peppers may develop dark, sunken areas in the fruit. Low calcium levels can also make plants more vulnerable to diseases and pests.

“Without enough calcium, plants can also suffer from browning leaf tips and weak stems,” says Josh Payne, owner of Classics, a landscaping company.

Many factors affect calcium availability in soil, including soil pH, climate, soil texture, organic matter, and other competing ions. Minerals like magnesium, potassium, and sodium can reduce calcium absorption in plants. Alkaline soils tend to have more calcium than acidic soils. Clay soils have higher calcium levels, while sandy soils usually have lower calcium content. 

How to Add Calcium to Plants Naturally 

Egg Shells or Oyster Shells

Adding crushed egg shells or oyster shells to the soil is a natural way to boost your plants' calcium. Add the shells to your compost or top layer of soil. Over time, this will increase the calcium that flows to your plants. 

“The used chemicals in the crushed eggshells dissolve over time in the soil and impart calcium,” Wilson says. “This is one of the easy, timeless approaches to integrating kitchen waste in your garden.”

Dolomite or Gypsum

Another natural option is dolomite, a mineral that adds calcium and magnesium to soil. Gypsum also offers calcium and sulfur, which help plants grow. Adding gypsum to soil improves its structure, enabling better root growth and drainage for plants. 

Limestone

Limestone is another way to add calcium to plants. If your soil is acidic, limestone can help neutralize it. It offers a slow-release form of calcium. “Limestone also raises pH, adds calcium to the soil, and enhances its structure and fertility,” Wilson says.

To add gypsum or limestone to your soil, spread it evenly over the top layer or mix it into the soil before potting new plants. 

How to Add Calcium to Plants Using Synthetic Fertilizers

If your plants need a quick calcium boost, synthetic calcium fertilizers can help. However, using too much fertilizer can harm your plants, so conduct a soil test and adjust your application amount accordingly.

“Synthetic sources like calcium nitrate or chloride offer a quick fix for deficiencies but should be used cautiously to avoid over-fertilization,” says Dennis Sons, CEO of TN Nursery. “You can use a liquid calcium supplement directly on the soil or as a foliar spray for a more immediate impact.”

If your plants exhibit signs of calcium deficiency and need help fast, you can apply synthetic calcium in spray form. “Spray calcium-rich sprays onto leaves for quick uptake,” Wilson says. “This is most crucial during rapid growth or in stressful periods.”

How Soil pH Affects Calcium Absorption

If your soil is too acidic, it will be harder for plants to absorb calcium. Limestone can help make acidic soil more alkaline. “Optimal pH for calcium availability is around 6.5. Frequently monitor soil pH and adjust it to bring this nutrient into optimum availability,” Wilson says.

Best Practices for Calcium Management in Plants

Testing the soil and monitoring your plants’ health is crucial throughout the process of adding calcium to plants. Regular watering is also essential to help your plants absorb calcium. A balanced fertilizer can ensure your plants get all the nutrients they need. “Balanced fertilizers and organic amendments will continue to support an adequate nutrient supply, including calcium,” Wilson says. 

Good gardening practices, such as crop rotation, can also ensure that your plants get the nutrients they need, including calcium. “Rotating crops and using cover crops to prevent calcium depletion in the soil are also beneficial,” says Sons. "Consistent watering is essential because calcium is transported with water in the plant."