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The Importance of Phosphorus for Cannabis Buds

By Michelle Pugle

Cannabis cultivation requires an art-and-science blend of macro and micronutrients to grow healthy, robust buds. 

As growers, we’re always working to achieve a moving target of optimal nutrients. Now, with other macronutrients like nitrogen and potassium, there’s a potential of soil toxicity if you dose in excess. With phosphorous, not so much.

Phosphorous is responsible for photosynthesis and carbohydrate utilization. It’s internalized by the plant in large quantities, especially during flowering and budding stages when it’s particularly hungry. So while you still want to do a standard soil test before adding any nutrients, phosphorous is more forgiving if you add too much. 

Phosphorous Deficiency 

Phosphorous deficiency is more likely to occur than toxicity. Your plants can be affected at any time during their growing cycle, but are at particular risk during flowering and budding. 

Look out for the following signs of phosphorous deficiency in your plants: 

  • Yellowing or browning of older plant leaves
  • Darkening of older plant leaves
  • Leaves getting shiny or exhibiting a blotchy appearance
  • Leaves curling downward
  • Bright red stems or purplish stems (normal on own, but significant when combined with other signs)
  • Thicker, drier, stiffer leaves

It’s important to note, though, that while this is something to watch for, it is quite uncommon for home growers to experience. The organic nutrients you feed your cannabis plants during their lifecycle should be sufficient to avoid phosphorous deficiency. 

If you do notice these signs, it could be signalling another deficiency or a root pH problem. Do another soil test and visual examination before deciding whether or not to add more organic fertilizer.