"Plants that are deficient in phosphorus are stunted in growth as well as they typically have a very unusual dark-green coloration to them. There could also be the development of anthocyanin pigments that give off a reddish-purple color in the cases of extreme phosphorus deficiencies. If your plant is exhibiting these types of discolorations, then the time to act is right now if the plant is to grow to its potential. These different colorations could be natural from your plant species, however. A few more symptoms to look for include a significantly lesser leaf expansion and a much smaller leaf surface area. Less leaves on the plant could also be the side-effect of low phosphorus levels. Also, be sure to check that the root mass looks appropriate and strong as lessened root growth is a very strong indicator of a low P level in your soil. Some of the other effects that a lower level than needed of P could include delayed maturity, poor quality forage, fruit, vegetable and grain crops, as well as a much higher sensitivity to plant illness." Phosphorus In Plants and Soils « Dyna-gro Blog Understanding Soil Phosphorus http://www.soils.wisc.edu/extension/materials/P_Understanding.pdf Bone char: a clean and renewable phosphorus fertilizer with cadmium immobilization capability. Bone char: a clean and renewable phosphorus fertilizer with cadmium immobilization capability. - PubMed - NCBI Biochar of animal origin: a sustainable solution to the global problem of high-grade rock phosphate scarcity? Biochar of animal origin: a sustainable solution to the global problem of high-grade rock phosphate scarcity? - PubMed - NCBI