What Is Dolomite Lime? | Soil Amendment Basics

Dolomite lime is a limestone-based soil amendment that raises soil pH and supplies both calcium and magnesium, typically applied when soil tests show acidity plus magnesium deficiency.

A bag of dolomite lime doesn’t look like much—grayish granules or powder that could pass for crushed gravel. But in acidic soil, it’s one of the most practical fixes a lawn or garden can get. Whether you’re fighting moss in a shady lawn or watching tomato blossoms rot on the vine, the mineral composition of dolomite lime addresses two problems at once: low pH and missing magnesium. The catch is that it only works on soils that actually need both, which is why the first step isn’t buying a bag—it’s running a soil test.

What Exactly Is Dolomite Lime Made Of?

Dolomite lime comes from dolomite rock, a mineral composed mainly of calcium magnesium carbonate—chemically written as CaMg(CO₃)₂ by the U.S. Geological Survey. When ground for agricultural use, it’s typically about 20% calcium and 10% magnesium, though those numbers shift depending on the quarry and processing method. The Minnesota Department of Agriculture gives a comparative breakdown: dolomite runs roughly 21.7% calcium and 13.1% magnesium, versus calcitic lime at 40% calcium and only trace magnesium. The calcium carbonate equivalent—a measure of how effectively it neutralizes acid—varies but can exceed 100% in high-quality material.

What Does Dolomite Lime Do in Soil?

Dolomite lime does two things at once: it raises soil pH toward the 6.0-to-7.0 range where most lawn grasses and garden vegetables thrive, and it adds magnesium that plants need for chlorophyll production. Magnesium deficiency shows up as yellowing between leaf veins on older leaves, especially in sandy or heavily leached soils. The distinguishing feature versus plain calcitic lime is that magnesium—if your soil already has adequate magnesium, adding dolomite creates a nutrient imbalance. That’s the main reason experts warn against using it without testing first.

How to Apply Dolomite Lime the Right Way

When to apply it

Apply dolomite lime 2 to 3 weeks before planting if you’re correcting pH and nutrient levels simultaneously. For established lawns, apply in spring or fall when rain can work it in.

How much to use

Rates depend on your starting pH and soil type. A typical lawn rate on acidic soil (pH below 5.5) is 25 to 50 pounds per 1,000 square feet. For container mixes, 1 to 2 tablespoons per gallon of acidic soil is a common starting point. Always follow your specific soil test’s recommendations rather than guessing.

How to work it in

Mix dolomite lime into the top 6 inches of soil for best results, or topdress and water it in. It works slowly—several weeks to months—because it’s a rock powder that must dissolve in soil moisture before it can change pH. Don’t expect fast results. For a quicker option, consider our tested recommendations for the best dolomite lime products that include verified calcium carbonate equivalent values and particle-size data.

Common Mistakes Gardeners Make with Dolomite Lime

• Using without a soil test. This is the #1 error. If your soil already has enough magnesium, dolomite pushes it too high and blocks potassium uptake.
• Confusing it with calcitic lime. Calcitic lime (calcium carbonate with little or no magnesium) is the right choice when magnesium is adequate. Picking the wrong one wastes money and may create new nutrient problems.
• Expecting fast results. Dolomite lime works slowly compared with quicklime or liquid fertilizers. It’s a long-term correction, not an emergency fix.