Different plants require different secondary nutrients to thrive however there are several main ones that most plants use these are Calcium (Ca), Magnesium (Mg), Sulfur (S) (CalMagSul).
Calcium provides various structural building blocks in cell walls and membranes. Because of how much calcium most plants use, it is almost considered a macronutrient.
Magnesium is essential for many plant functions. Magnesium is the central element of all forms of the chlorophyll molecule [Chlorophyll a (C55H72O5N4Mg), Chlorophyll b (C55H70O6N4Mg), Chlorophyll c1 (C35H30O5N4Mg), Chlorophyll c2 (C35H28O5N4Mg), Chlorophyll d (C54H70O6N4Mg), Chlorophyll f (C55H70O6N4Mg)], it is essential in nutrient uptake control, sugar synthesis, and plant oil and fat formation. Magnesium is also a carrier of Phosphorus.
Sulfur is necessary in the formation of chlorophyll. Sulfur also helps the plant’s resistance to disease, aids in growth, and in seed formation. In addition, sulfur is used in the processes of producing proteins, amino acids, enzymes, and vitamins.