Soil magnesium levels vary across the United States, with higher concerns in more humid places. Many plants require magnesium, therefore it’s important for gardeners to understand why and how to incorporate magnesium into the soil.
The first step in creating a healthy, flourishing garden is to get the soil tested to determine its pH and nutrient levels.
For use in gardening soil, magnesium can be found in both soluble and insoluble forms. Dolomitic lime is the preferred insoluble form because it contains magnesium while calcitic lime does not. Epsom salts, commonly known as magnesium sulfate, are a soluble form that also includes calcium and sulfur. Magnesium oxide and sulfate of potash magnesia are two other soluble forms.
This is why you should always check the nutrient and pH levels of your garden soil before planting anything. Soil that is already alkaline should not be treated with dolomitic lime, and soil that has an excess of potassium should not be treated with a chemical containing potassium oxide. It’s important to know the nutrient levels already present, such as calcium, so that you can add the right amount of magnesium. Guessing instead of testing can be harmful to the plants.
Soil that is poor in magnesium can be remedied by adding Epsom salts, which are widely available and have a high solubility and speed of action. Some caution is warranted, though, before you start using Epsom salts. Although there is some evidence that Epsom salts improve plant health, this is highly dependent on the plant’s overall nutritional status.
Soils low in magnesium, for instance, are frequently older, acidic soils. Using dolomitic limestone and waiting for as long as it takes (lime amendments work slowly) to alter the pH and magnesium levels may be the best course of action in such a situation. In this situation, using Epsom salts would not alter the pH significantly, making the soil unusable for many types of plants. The disadvantage of utilizing dolomitic lime is that you must monitor the soil’s calcium levels; adding organic matter to amend the soil can be an alternative to using dolomitic lime.
If pH isn’t an issue but magnesium is, consider applying Sul-Po-Mag, a fertilizer comprising sulfur, potassium, and magnesium; Epsom salts won’t remedy severe deficits. In addition, if you decide to use Epsom salts, remember to use them carefully and according to the specific formulations suggested for each plant. For instance, some plants thrive with an infusion of magnesium into the soil, while others respond better to a foliar spray.