How to Add Calcium to Soil?

There are several effective methods to add calcium to your soil, ranging from readily available amendments to more natural solutions.

Methods to Increase Soil Calcium

Here's a breakdown of common methods:

Lime (Agricultural Lime): One of the most common and effective ways to raise calcium levels and increase soil pH (making it less acidic). Different types of lime exist, including:
- Calcitic Lime: Primarily calcium carbonate.
- Dolomitic Lime: Contains both calcium and magnesium carbonate. Choose based on whether your soil also needs magnesium.
Gypsum (Calcium Sulfate): A good option if you need to add calcium without significantly altering the soil pH. Gypsum also helps improve soil structure, particularly in clay soils.
Bone Meal: A slow-release source of calcium and phosphorus. It's a good option for adding nutrients while planting.
Clamshell Flour/Oyster Shell Flour: A natural, slow-release source of calcium derived from ground seashells.
Wood Ash: Contains calcium, potassium, and other trace minerals. Use sparingly as it can also raise soil pH significantly. Avoid using ash from treated wood.

The best calcium source depends on your soil's specific needs:

Soil pH: If your soil is acidic (low pH), lime is a good choice. If your soil pH is already high, use gypsum or another pH-neutral option.
Nutrient deficiencies: Consider what other nutrients your soil needs. Bone meal provides phosphorus along with calcium. Dolomitic lime provides magnesium.
Soil type: Gypsum is particularly beneficial for clay soils, helping to improve drainage.
Release rate: Bone meal, clamshell flour, and oyster shell flour are slow-release, providing calcium over a longer period. Lime and gypsum are faster-acting.

Soil Test: The most important step! A soil test will tell you your soil's pH, calcium levels, and other nutrient levels. This information will help you choose the right amendment and application rate.
Calculate Application Rate: Follow the recommendations from your soil test results or the product label. Over-application can be harmful.
Application: Spread the amendment evenly over the soil surface and incorporate it into the top few inches. For established plants, gently work the amendment into the soil around the base of the plants, being careful not to damage the roots.
Water: Water thoroughly after application to help the amendment start breaking down and releasing calcium.

Amendment	Calcium Source	Affects pH?	Other Benefits	Notes
Calcitic Lime	Calcium Carbonate	Raises pH	Can improve soil structure	Use if soil is acidic
Dolomitic Lime	Calcium & Magnesium Carbonate	Raises pH	Adds Magnesium	Use if soil is acidic and magnesium deficient
Gypsum	Calcium Sulfate	Neutral	Improves soil structure (clay soils), aids drainage	Won't change pH
Bone Meal	Calcium Phosphate	Slightly Raises pH	Adds Phosphorus	Slow release
Clamshell Flour	Calcium Carbonate	Raises pH	Natural, slow release
Wood Ash	Various Calcium Compounds	Raises pH	Adds Potassium, other trace minerals	Use sparingly; test soil pH frequently