The information below was originally from SaltWorks. Their section on Gardening and Epsom Salt has been newly updated.  Click on the link to learn more.

Gardening and Epsom Salt

Epsom salt has become a popular and well-reputed supplement in organic gardening. It is an ideal answer to a variety of organic gardening needs. Both cost effective and gentle on your greenery; an affordable and green treatment for your well-tended plants–both indoors and out. Epsom Salt, magnesium sulfate, is one of the most economic and versatile salt-like substances in the world. It helps to create lush grass, full roses, and healthy, vibrant greenery. It has long been considered a gardener's secret ingredient to create a dramatic impact. Epsom salt enhances the soil's capabilities. Magnesium and sulfate are two minerals that are crucial to healthy plant life. It does not build up in the soil; it is safe to use often. Magnesium assists seed germination; helps strengthen the plant cell walls. It is crucial in photosynthesis and the creation of chlorophyll. It helps the plant to soak up phosphorus and nitrogen, which serve as vital fertilizer components for soil. Magnesium is believed to bring more flowers and fruit to plants, increasing the bounty and beauty of green space. Sulfate is equally important nutrient for plant life. It is essential to the health and longevity of plants; aides in the production of chlorophyll. It joins with the soil to make key nutrients more effective for plants, including nitrogen, phosphorus and potassium. It also works in conjunction with magnesium to nourish and bring health benefits for your garden.

Houseplants and Epsom Salt

Dissolve 2 Tablespoons per gallon of water. Use this solution once a month or as often as desired. It can clear up accumulations of natural salts in the pot leading to a revival in plant health. As a general rule, plants need plenty of indirect sunlight to fully utilize Epsom salt. Potted vegetable plants will produce more fruit or vegetables on a plant. This is particularly beneficial to apartment dwellers and those with little or no personal yard space. This creates a wonderful way to easily and effectively grow food.

New plantings and Epsom salt

Prep garden soil by sprinkling up to 1 cup of Epsom salt per 100 square feet (10'x10'). Work into the soil before seeding or planting. This helps seeds germinate better and start a strong and healthy growth. It is also very beneficial for plants because it aids in the transition and planting shock. Epsom salt is advised for use with all fruits, vegetable and herbs except sage. It is safe and effective at any stage of a plants growth. To use a tank sprayer: use 1 tablespoon per gallon of water. Spray on foliage or on soil early or late in the day, once per month. Tomatoes and Peppers are prone to magnesium deficiency later in the growing season. Plants with yellow leaves and less production are showing magnesium deficiency. One or two tablespoons of Epsom salts can be added to the planting hole to help this issue. Later in the growing season, it can be worked into the soil or the plant can be sprayed with the above sprayer solution. Flowering plants including roses blossom more vibrantly and beautifully with Epsom salt use. These two minerals are vital to all plants. Shrubs and trees can utilize Epsom salt also. Use 1 tablespoon per 9 feet of shrub or tree or root area. Work into the soil, then water. For the best results use Epsom salt 3 or 4 times per growing season. Lawns benefit in the same way from Epsom salt use. It helps prevent yellowing; and helps create a softer, greener, lusher lawn. Can be applied in a tank sprayer or apply pounds per 1250 sq. ft (25'x50'). Make a concentrate solution for tank sprayer. If applying dry, water very well to dissolve salt crystals.