Epsom salt is most commonly used on pepper, tomato and rose plants. This is because epsom salt is made from magnesium. Many pepper plants are planted in soil that is deficient in magnesium. The magnesium from the epsom salt is quickly absorbed by the plant to give it the nourishment it needs to grow. The epsom salt can be applied in spray form for the best results. Do not simply rely on epsom salt if your soil has a severe deficiency in magnesium. It will work, however, for low to moderate deficiencies. Spray the epsom salt solution on the pepper plants again when they first begin to flower.