Those other trace minerals your plant can't live without
Magnesium (Mg) and Iron (Fe) are the "chlorophyll helpers." They're both important to the plant's production of chlorophyll. Magnesium, in fact, makes up the core of the chlorophyll molecule. Dolomitic lime and epsom salts are good sources of magnesium. To supply your plants with iron, try spraying liquid seaweed or chelated iron.
Calcium (Ca) and boron (B) are essential to any plant's plumbing system. Calcium is essential for proper water uptake, and both are important for proper cell formation. Calcium is present in gypsum, lime, and oyster shells. Boron is available in borax and a chelated boron spray.
Sulfur (S), zinc (Zn), and manganese (Mn) are the "catalysts" that help other nutrients such as nitrogen become usable by your plants. Gypsum and flowers of sulfur are good sources of sulfur. The others are available in chelated form, usually as a spray.
Overwhelmed? Chill out. Remember, all of the above can be found in a simple plant food sprays.