Phosphorus in Plants



Phosphorus is associated with fruit production in the minds of gardeners because it is the most important element for germination and growth.

Phosphorus deficiency

Phosphorus deficiency
Phosphorus deficiency in corn

Phosphorus is typically associated with fruit production in the minds of gardeners, and little wonder. This mineral is believed to be the most important element for germination and growth. It is a structural component of both DNA and RNA, and is also part of ATP, the energy source of the cell. Therefore, without phosphorus, plant cells cannot divide, grow, or transfer energy.

But there’s more. Phosphorus is also part of the protein molecule, as well as a constituent ingredient of phospholipids, fatty substances key to cell membrane development.

Translating this scientific terminology into practical considerations observable in the field, phosphorus is responsible for the following:

  • Improving seedling vigor.
  • Promoting root development.
  • Increasing tolerance to adverse weather conditions.
  • Making fruit and seed development possible.

Natural Sources

Phosphorus in Plants
Rye fertilized with phosphorus (right) compared to a control

There are many natural sources of phosphorus available. Mineral sources include rock phosphate and crushed granite.

On the plant-based side of things, composted yard waste, such as leaves and grass clippings, frequently contains phosphorus. Alfalfa meal, soy husks, and sunflower hull ash also supply this mineral.

Animal manures contain phosphorus, with chicken and swine manure being particularly rich sources. Bat guano is another option.

Finally, bone meal is considered one of the most potent sources of phosphorus available.


Phosphorus deficiency
Phosphorus deficiency

Phosphorus deficiency is extremely common in plants and can be a serious limiting factor in growth. This mineral is released very slowly from the underlying parent rocks, while at the same time most plants have high phosphorus requirements. Furthermore, any deficiency in soil microorganisms will impair a plant’s ability to take up whatever phosphorus is available.

The symptoms of phosphorus deficiency tend to be extremely vague, and indeed may not be visible except in extreme cases. However, known symptoms include:

  • Slow growth.
  • Slight lack of leaf luster in trees.
  • Unusually dark green leaves that gradually turn red, noticeable first on the lower leaves.
  • Burnt leaf tips.
  • Irregular brown or black dead spots on leaves.
  • Leaf death.
  • Delayed fruit set.
  • Dead spots on fruit.
  • Failure to set seed.

Phosphorus deficiency should be corrected with the application of a natural phosphorus source. Boosting soil microorganism levels through good soil care practices should also help.


Phosphorus toxicity is typically caused by the overuse of high-phosphorus fertilizers (note that this includes manure). However, it can also occur if plants are watered with grey water from homes using phosphorus-based detergents.

Generally, phosphorus toxicity is not too much of a concern for the plants themselves. Phosphorus runoff and subsequent water pollution and algae blooms are typically more of a problem.

However, plants that receive too much of this mineral may display the following symptoms:

  • Withering.
  • Overall yellowing.
  • Iron deficiency.
  • Zinc deficiency.

Because excess phosphorus causes few problems in field or garden plants, reducing or discontinuing phosphorus use will solve the problem quickly.

Complete Series

Minerals in Plants

Minerals in Plants

Improving Your Garden Soil