Magnesium is the central atom in chlorophyll and so is essential in photosynthesis. Furthermore magnesium influences other pigments and physiological processes. This makes it an essential element in the development of the plant.
Magnesium can be directly absorbed by the plant and therefore the effects can be seen quite soon. It can be used as a fertiliser for magnesium deficiency and as a supplementary nutrient to stimulate the growth and bloom.