Cultivating fruiting and flowering plants in hydroponics requires less phosphorous levels than potassium and even nitrogen. In hydroponics, phosphorous levels that are too high tend to lock out calcium, magnesium and trace minerals. On the other hand, plants grown in soil need higher phosphorous levels due to clay colloidal particles that bind up phosphorous. Microbes in the soil also compete for the phosphorous.When cultivating fruiting and flowering plants in soil, growers usually need to double or triple phosphorous levels, unlike hydroponics, thus making the 1.5-4-5 formula ideal for soil applications.