Epsom salts are rich in magnesium, which plants need in order to grow well, particularly roses and tomatoes. You can mix 1 cup of Epsom salts with 1 gallon of water and water your plants. Try not to get it on the leaves if you water during the day. You can also sprinkle some of the salt into the soil. Palm trees especially need magnesium. I sprinkle it on the ground about eight inches around the whole trunk in March, July, and September.