What Is Dolomite Used for With Plants?

Dolomite powder is a limestone compound that contains calcium and magnesium. The best mixtures contain 8 to 12 percent magnesium and 18 to 22 percent calcium. These elements help influence the pH of the soil and provide valuable nutrients to plants. Dolomite can often contain sodium, but it should only be 0.2 percent sodium or less. More sodium can change the salinity of your soil, which can kill many plants.

Dolomite limestone is best used to change the acidity, or pH, of the soil. Start with a soil pH test, which you can buy at garden centers, to determine the existing pH. Most plants do best with a pH of 6.0 to 7.4. If your soil registers with a pH of 5.9 or below, dolomitic lime can help raise the pH to make the soil more plant-friendly. Some plants prefer acidic soils, where the pH is lower, so check on your specific plants’ needs before adding the dolomite.

Some plants, especially vegetables that have lots of seeds inside, such as tomatoes (Lycopersicon esculentum), need extra calcium as they grow, and the dolomite is an excellent way to provide that nutrient. Dolomite also helps provide magnesium and other nutrients that are beneficial to growing plants. Magnesium excels at neutralizing acid when the garden soil is too acidic for the plants that will grow in it.

You can add dolomite to your yard, flower beds and vegetable gardens any time there’s no frost or freezing temperatures, but it’s best to add it in spring or fall. Pick a day when no rain is predicted so it won’t wash off the soil before being absorbed. Also choose a non-windy day, as dolomite for garden use is often in a powdered, talc-like form. With vegetables, adding the dolomite before you plant gives the seeds an extra boost, then you can add more as necessary as the plants are growing. Adding dolomite into the growing medium before planting helps prevent some type of plant problems and rot usually caused by lack of calcium.

If you’re adding it to an empty garden where you plan to plant flowers or vegetables, turn it into the top 6 inches of the soil before you plant. To change the soil’s pH, determine how much you need and spread it on top of the soil. For example, if your soil has a pH of 5.5 and you want to raise it to closer to 6.5, add 10 pounds of dolomite per 100 square feet of space. That would be equivalent to a 10-by-10-foot bed or a 5-by-20-foot bed. To prevent burning existing plants, spread the applications out throughout the growing season.