When added using a product like Epsom Salts, it should not trigger new growth like nitrogen does so add some if your soil is defficient. I have read of some people mixing 1 tbsp in 1 gallon of water. Symptoms are chlorosis of older leaves, beginning at the leaf tips. Veins remain green at first but later lose color. Brown, dead areas appear on the tips and margins of lower leaves which soon drop off. They may develop reddish purple blotches on their upper surfaces. If magnesium is available in the soil but the soil pH is too acidic, the plant will not be able to absorb much magnesium; add some dolomite to the soil as well.