Epsom Salts
With what compound can you soak your feet, ease your back ache, brew beer, solve your constipation, treat your aquatic plants and fish, fire proof your Christmas tree and fertilize your roses, peppers, and tomatoes? Epsom salts is the common element to all of these "cures". Epsom salts were first used in Epsom, England, and have been used for hundreds of years to ease the aches and pains of the weary gardener in hot mineral baths. Epsom salts is really magnesium sulfate, about 10% magnesium and 13 percent sulfur. The two components are vital to the health of plants, but whether the source should be from Epsom salts, is highly debated. Magnesium is necessary to strengthen cell walls, and aids in the uptake of nitrogen, phosphorus and sulfur. Sulfur, is essential to protein production, and plant enzymes. In two soil tests done on Benicia soils, (Vallejo soils will be similar) showed and already high Magnesium test of 4ppm and 6ppm. Lack of Magnesium is not a problem here, but sulfates on the other hand were almost nil. The sulfur or acidifying components are missing from our soils. In old soils, that have a low pH, such as those in the Pacific northwest or the Southeast, or soils with a pH above 7 and high in calcium and potassium, as are common to many Western soils, may have low magnesium levels. But, our two soil tests showed pH of 6.5 and 7.2, high calcium, and medium to high potassium counts. The choice of using Epsom salts vs. other forms of sulfur delivery seem to be most relevant, since Magnesium is already in abundance.
Rose enthusiasts are of mixed opinion to the importance of Epsom salts. Being a sulfate, it will generally lower soil pH, making it more acidic, not bad since our soils are slightly alkaline for the most part. Those that use it report that it will stimulate basal breaks when applied with some form of nitrogen. This means new growth from the lower part of the plant, a desirable thing for rejuvenation of new growth. The amount used varies from a tablespoon to 1/2 cup sprinkled around the drip line in the spring and/or the fall, or as a foliar spray, the amount varying depending on the gardener’s experience of tradition.
Little scientific study has been done in determining the usefulness of Epsom salts in soils that are already sufficient in one or both of these elements. In the May/ June issue of "National Gardening Magazine", reports of two studies in progress at universities on peppers, tomatoes and roses to measure any appreciable effects on the growth of these plants under drought and non-drought conditions. They also did an informal study of 6 gardeners across the country growing identical plants, with varying results. One gardener in our own Alameda, California reported about her "Gypsy" peppers, that "The fruits were much bigger, almost twice the size. They were much bigger, almost twice the size. They were juicier, sweeter, and triple the thickness of the untreated peppers."
If you decide to use it, there are preparations available in nurseries with recommended guidelines printed on the bag. It is recommended to go this route rather than haphazardly mixing Epsom salts bought in the supermarket. Since it is a salt, an over use of this product, especially in summer of drought years, can lead to a build-up of salt in the soils. Clay soils are especially prone to holding onto salts.
Epsom salts mainly used to solve Magnesium deficiency problems, symptoms of deficiency in roses, tomatoes, and peppers, plants which require higher amounts of this element, are yellowing of leaves between the veins, leaf curl, stunted growth, and lack of sweetness the fruit. Unfortunately, all of these symptoms mimic other deficiencies too, and a soil test is really the best way to test for deficiencies in soils. To get the benefits of sulfur, any of several products can be used. Animal manures, and chemical fertilizers such as ammonium sulfate can be used. An excessive use of liming materials will cause a need to acidify your soil. Granular, super-fine dust, or wettable sulfur man be used to decrease soil pH. Granular sulfur is easiest for lawns due to the ease of application via cyclone spreader and it is less likely to burn foliage. If you have over done it with lime, it will take only 1/3 the amount of sulfur to decrease the soil pH 1 unit as it did to increase soil pH 1 unit. Do not use more than 5 to 10 pounds of sulfur per 1000 square feet per application and repeat if necessary only once every 2 to 3 months. This is strong stuff, and if misused, it will burn your plants, use as directed. Sulfur oxides in the soil when mixed with water form sulfuric acid. Twice as much does not make it twice as good. This may be useful in correcting soil pH for the short term, but a better solution is with continual addition of composted manure, and organic matter. Gypsum can be added to help maintain the pH at a certain level once you have reached the level you desire. A pH of 7 is neutral.
The jury is still out on Epsom salts. A lot of our home remedies are based on folk lore that was passed down through generations, perhaps from the grandmother who brought the mineral salts from Epsom, England, who tossed the bath water out onto her roses. But what kind of soil were the roses planted in?
Carol de Maintenon is a member of Garden Writers of America and owner of Benicia Garden & Nursery.
