phosphorus for cannabis

Phosphorus And Cannabis Plants

Phosphorus is one of the three primary nutrients cannabis needs for healthy growth. Find out the functions of phosphorus and how you can spot, treat, and prevent phosphorus deficiency.


Phosphorus is one of the three primary cannabis nutrients needed in all stages of growth. In this guide, we cover the functions of phosphorus and let you in on how to identify, treat, and prevent phosphorus deficiency and toxicity.

What Is Phosphorus?

Together with nitrogen (N) and potassium (K), phosphorus (P) is one of the essential nutrients cannabis plants need for healthy growth. It is classed as a primary macronutrient due to its important roles in various plant functions. Your cannabis plant depends on the availability of phosphorus during all phases of its development, where it requires the element in relatively large amounts.

Phosphorus is essential for photosynthesis, plant metabolism, and nutrient uptake. It is particularly important for new growth and early stage root development, but also for bud formation and yield. A lack of this mineral (or an excess) will lead to your plants getting sick.

Commercially available cannabis nutrients, especially those formulated for flowering, usually contain more than sufficient amounts of phosphorus. But phosphorus deficiencies or toxicities are possible, most often due to pH issues, poor soil quality, improper nutrients, or certain environmental factors.

The Phosphorus Cycle

Phosphorus replenishes itself in a biogeochemical cycle in the ecosystem known as the phosphorus cycle: Plants that have taken up phosphorus from the ground are eaten by animals. Through animal droppings, the element is replenished in the subsoil. Microbes process the element and make it available for plants once again, thus closing the phosphorus cycle.

The element is also washed out from the land and carried into the seas due to erosion and rainfall. This is why marine life, such as fish and algae, is particularly rich in phosphorus. The element returns to the land through seabird or fish droppings, and in some areas also through natural geological processes when land emerges from the sea.

Why Do Cannabis Plants Need Phosphorus?

Phosphorus plays an important role in essential biochemical actions such as synthesising proteins and carbohydrates. Here is a rundown of some of its crucial functions:

Promotes the growth of roots.

Increases resistance against diseases and pests.

Increases frost resistance.

Promotes optimal use of water in the substrate.

Increases bud quality and yield.

Benefits seed germination.

By boosting root growth, phosphorus can help reduce the duration of the vegetative phase.

Plays an essential role in plant metabolism, where it aids in the production of carbohydrates.

Phosphorus Needs During Early Stage

Right after germination, cannabis can live off the nutrients in the seed. Likewise, most commercial soils will already have sufficient amounts of phosphorus. Additional feeding will not be needed up until about week 3, when the plant has reached a height of approximately 15cm. Otherwise, providing extra nutrients too early in the plant’s life can negatively affect root growth and overall health of the seedling.

Phosphorus Needs During Vegetative Stage

When the plant has entered the vegetative growing stage, from about week 4 on, it will require an adequate feed rich in nitrogen, phosphorus, and potassium. Recommended nutrient levels for vegging are 200 ppm of nitrogen (N), 120 ppm of phosphorus, and 200–250 ppm of potassium. Exact feed rates, however, can vary depending on the strain, container size, and environmental factors. When using commercial cannabis nutrients, it is best to stick with the recommended doses.

Phosphorus is very important for cannabis plants. It holds a key position in cell metabolism and in the total energy transfer of the plant.