Discovered hundreds of years ago in the well water of Epsom, England, Epsom salt is actually not a salt but magnesium sulfate, a mineral compound containing 10 percent magnesium and 13 percent sulfur. Its proponents say that adding it to soil where tomatoes and peppers grow can produce larger and more flavorful yields. Gardeners also apply Epsom salts to roses, which, like tomatoes and peppers, require high levels of magnesium for optimal growth.
Need for Magnesium
While sulfur is not often deficient in garden soils in this country, magnesium deficiencies can become critical in the vegetable patch. Besides being essential for seed germination and the production of chlorophyll and fruit, magnesium strengthens cell walls and facilitates the plants’ uptake of other minerals, such as nitrogen, phosphorus and sulfur. Alkaline soils, with a pH above 7.0, and those high in potassium and calcium frequently test low for magnesium. These three minerals compete for uptake by plant roots, with magnesium often the loser, even if an adequate magnesium level exists. Tomatoes and peppers suffering from too little magnesium may display leaf curling, yellowing of the leaves between veins, stunted growth or lessened sweetness in the fruit. Dolomitic lime and other soil additives can increase magnesium, but Epsom salts have the advantage of being highly soluble, and the compound will not build up in the soil.
When to Apply Epsom Salts
Most experienced tomato growers have a special formula they like to place in the planting hole under the plant’s root system. For some, it is a tablespoon of Epsom salts. As the tomatoes’ roots grow in the first few weeks, they can tap into this nutrient reservoir. Beginning when the blossoms on your tomatoes or peppers first appear, apply a foliar spray made up of 2 tablespoons of Epsom salts to a gallon of water once a month, as a substitute for one regular watering. Every six weeks until harvest, work 1 tablespoon of the compound per foot of plant height into the soil around the vegetables. Early in the season, the Epsom salts should aid in root and cell development, photosynthesis and plant growth and stave off blossom-end rot. Used late in the season, the result should be greater tomato and pepper yield.
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Although little scientific research has been carried out on the effectiveness of Epsom salts as a soil amendment, the National Gardening Association conducted an informal test on the subject. Six members in different parts of the country each planted six “Gypsy” bell peppers. Each tester treated only three of their plants with Epsom salts. At bloom time, they applied a foliar spray of 1 tablespoon of the compound mixed into a gallon of water, then repeated the spraying 10 days later. For four of the six testers, the treated pepper plants grew larger and produced heavier fruit than the controls. The tester with the best results, from Alameda, California, reported that the Epsom salts had generated fruit almost twice the size of that from the untreated pepper plants. She described the sprayed peppers as sweeter, juicier and triple the thickness of their counterparts.
Most Likely to Benefit
Epsom salts should not be relied upon to correct severe magnesium deficiencies in the soil. The compound works best where soils are slightly lacking in the mineral. Where soils lean toward the alkaline side, with pH measurements above 7.0, or are high in calcium and potassium, adding magnesium sulfate will probably be beneficial. Many areas in the West fit this description. Epsom salts is inexpensive and readily available at drug and grocery stores.