^Trust me, the NPK ratios of these 'bud hardener' products are not in any way proper... especially not for organics.
Basically, they are designed with the assumption that only a small proportion of the total phosphorous applied is going to make it into the rhizosphere and be absorbed by the roots.
The phosphate ion is an anion, it has a negative (-) charge. Soils and organic soil-less potting mixes contain materials like humus (and clay), and to a lesser extent sphagnum and coco coir, which possess negatively charged 'sites' capable of loosely holding onto cations (+ charged ions) such as potassium (K+), one form of available N (ammonium NH4+), calcium and magnesium. This is known as cation exchange capacity, and while the cations are attracted to and adsorbed at these sites, anions like phosphate are repelled into the soil solution where they more easily leech away. There are also materials that would have positively charged 'sites' capable of adsorbing anions in the same manner to a lesser extent.
However, the phosphate anion is highly reactive and will easily form complexes with other components of the soil, thus making it unavailable to plants directly but still technically present. In living soil you have microbes (and fungi like mycorrhiza, especially) constantly seeking out compounds in the soil they can convert to plant available forms, directly in the rhizosphere. Mycorrhizal fungi don't do well with excessive amounts of phosphorous in the soil, they like to seek out and break off phosphate groups to bring back to the plant.
