Hi, I have got my hands on a bag of Jersey Greensand and a bag of rock phosphate. How can I use these to the best advantage? I have neutral soil (hydrangeas bloom pink) that is not clay and not particularly fertile. Lupins, hesperis, daisies, phlox, violets, peonies, rudbeckia, hepatica and iris do well. Should I spread it in the fall or is spring better? Can I spread it over lawns (full of botanical crocuses) and already planted perennial beds? The greensand is supposed to improve both heavy and light soils. Thanks for any info.