Phosphorus and Plants

• Phosphorus is among the most important plant growth nutrients and it plays a vital role in numerous biological functions. Phosphorus is integral to the process of photosynthesis whereby plants convert carbon dioxide into essential sugars. Phosphorus also determines plant size and structural integrity, as well as the size and quality of fruits and vegetables yielded by fruit plants. Plants deprived of sufficient amounts of phosphorus show stunted new growth and diminished structural strength.
  
  

Root Development

• Another important role of phosphorus in plant growth is development of root structures. Plants that do not receive enough phosphorus from soil do not establish root structures in soil as quickly or as healthily as those that receive sufficient phosphorus. Thus, when growing plants in soils that lack phosphorus, it is often necessary to supplement phosphorus into the soil using fertilizers or other soil amendments. Phosphorus additions to soil are so common, in fact, that gardeners long ago coined the adage "nitrogen for shoots and phosphorus for roots," to imply that phosphorus always stimulates root growth in plants.
  
  

Phosphate Fertilizers and Root Development

• Due in large part to the critical role played by phosphorus in root development, growers sometimes mistakenly add more phosphorus to soil than is needed for healthy root development. A carefully applied phosphorus fertilizer can stimulate healthy root growth, but an over-abundance of phosphorus in soil due to over-fertilization can harm the mycorrhizal micro-organisms that make plant root development possible and thus can actually inhibit proper root development.
  
  

Other Considerations

• The best way to avoid problems in plant root development due to an over-abundance of phosphorus in soil is to remember that fertilizer is not plant food. Phosphorus deficiencies in soil need to be addressed in order to increase the likelihood of healthy root growth, but over-use of fertilizer leads to more serious problems than if you had neglected to fertilize at all. Frequently test your soil for fertility and always use only the smallest amount of fertilizer possible to achieve the concentration of phosphorus that is most conducive to root development.