Answer: I've heard of using epsom salts around roses and tomatoes, but never around hydrangeas. Here's what the Epsom Salts Council has to say: "Epsom Salt is magnesium sulfate. Magnesium occurs naturally in soil, though not always in a quantity sufficient for all plants. Some soils start out with sufficient magnesium, but an abundance of rain can cause it to be washed out of the soil.
Generally speaking, rough, sandy soil is a sign that the soil is deficient in magnesium. Soils developed from peat bogs and alkaline soils also tend to be magnesium-hungry. And it's been reported that soils along the Atlantic coast tend to a magnesium-deficient.
Adding Epsom Salt to plants has been reported to enhance the color of blossoms and leaves, promote new flowers and fruit, improve the root system and improve the strength of stems.
Epsom Salt is safe to use and will not build up in the soil, even if additional magnesium isn't needed."
For additional information, you can visit the following website: http://www.epsomsaltcouncil.org/garden.htm
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