If you look at the plants' makeup, they're about 95% water. Of the "dry" mass, the vast majority is carbon, oxygen, and hydrogen (obtained from air and water) and nitrogen (obtained from fertilizers we apply). All of the other minerals, combined, make up about 1% of the plants' dry mass.
Orchids are particularly undemanding of fertilizer, because they are so slow-growing, compared to most other plants.
If you do the calculations of the chemical processes going on in plants, to gain 1 kg of mass - maybe 45 or 60 days for corn, a couple of years for a cattleya, a decade for a phal, or a lifetime for a tiny pleuorthallid - they must absorb and process about 200 liters of water, but only 10g of nutrient minerals!
Studies have shown that the "throughfall" and "trunk flow" water reaching epiphytes after cascading through a tropical forest canopy has a mineral content typically below 15 ppm, and the vast majority of that is nitrogen.
K-Lite fertilizer (12-1-1-10Ca-3Mg) was developed to try to mimic that, and my recommendation of using only a little, but using it frequently, is intended to mimic what the plants see in nature.
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