Analysis: 0-18-0. Superphosphate is an inexpensive and effective source of phosphorous that plants and bulbs need to produce healthy roots, stems and blooms. Superphosphate can aid root growth by adding a little extra phosphorus in the form of bonemeal superphosphate. Sprinkle it directly onto the rows just before planting the seeds, raking the bonemeal into the top inch of soil so it can be used by the young seedlings when they come up. A handful is about right for every four to six square feet. The same porportion applies when being utilized for existing plants, but only apply underneath the drip line. Superphosphate won't burn the seeds or plants, as the plants will only use as much as they need.