Phosphorus is one of the three main nutrients needed for healthy plant growth. When purchasing commercial fertilizers, the center number of the three is phosphorus, with the first being nitrogen and the third being potassium. While most soils have some phosphorus content, most do not have enough to meet the plant's needs. In organic gardening, phosphorus needs to be supplied by natural means. Replacing the phosphorus in fertilizer requires planning before you begin your garden then must be maintained each year thereafter.
Purchase a soil test kit from a garden center the at least six months before you plant to start your garden. Perform the test following package instructions. This will tell you how much of each nutrient needs to be added to the soil for the type of garden you are planning.
Apply bone meal or composted poultry manure, which are both rich in phosphorus, to the garden bed at the recommended rate the fall before starting the garden. Till it into the soil with a power tiller or a hoe.
Lay a 3-inch layer of straw mulch over the bed after fertilizing. This prevents the phosphorus from leaching out during snow melt. Remove the mulch before spring planting.
Plant the garden as desired. Apply a second treatment of bone meal or poultry manure to the garden once flower buds set on fruiting vegetables and ornamental plants or at mid-season for foliage plants.