Hi. I just began testing the soil in my garden beds. (I moved into my house two years ago, and many of the perennials I planted last year seem not to have survived.) So far, the soil is testing as depleted of nitrogen and phosphorous. It's OK for potash. PH is mostly slightly acidic. Can you tell me how best to add nitrogen and phosphorous to the soil, with an eye toward improving long-term condition? I am trying to grow flowers. Thank you for any info!