Epsom salts is a form of magnesium, which is an element that is essential for plant photosynthesis. This means that virtually all plants can benefit from the addition of Epsom salts if they are being grown in soil that is magnesium deficient. The most reliable way to determine if your soil is lacking magnesium is to perform a soil test. Some plants are more likely to benefit from high levels of magnesium, including tomatoes, peppers, and rose bushes. Epsom salts will improve how quickly these plants grow and deliver a more bountiful crop of food or flowers. Plants like beans and leafy vegetables are less dependent on magnesium and will grow well even if magnesium levels are low.