For example, in the case of iron deficiency diseases, many people use rusty nails in the tub. Numerous people on Youtube are following this advice. The result? Tetanus can be caused by eating a rusty nail if your quote is bad, but your tree will not recover. Suffering from iron deficiency disease, even a ton of rusty nails at the base of your seasonal flowering plant will not hurt. Adding vinegar to the soil can increase the acidity of the soil.