Monterey Epsom Salts is a source of magnesium that is essential to plant development. It is required by plants to produce chlorophyll.  Leaf yellowing is a magnesium deficiency symptom.  Epsom Salts helps plants absorb phosphorus, increase plant's natural resistance to disease. It's absorbed by both the leaves and roots.  Monterey Epsom Salts stimulates rose bloom & cane growth.  Can be used as a foliar spray or added to soil.  Tomatoes benefit from a teaspoon added to planting hole at time of transplanting.  4 lbs covers 500-1000 sq ft.