Check your plants for a magnesium deficiency. Plants suffering from this common malady often have yellow coloring in their leaves and may drop their lower leaves. If your plants aren't experiencing a mineral deficiency, Epsom salt may not be your best choice.
Measure your tomato plant from the soil to the top tip.
Add 1 gallon of water to your watering can.
Drop 1 tablespoon of Epsom salt per foot of your tomato plant’s height into the watering can.
Add 1 tablespoon per foot for each individual tomato plant. For example, two three-foot tomato plants would require 6 tablespoons of Epsom salt.
Water your tomato plants with the Epsom salt mixture once every two weeks.