Phosphorus is one of the most important nutrients the cannabis plant needs during both vegetation and flower. This nutrient is much more used during the flowering phase as it helps tremendously with bud growth! As with other deficiencies, signs will show on the oldest and more lower leaves on the plant and then will slowly work its way up to the top. A lack of phosphorus will initially cause the fan leaves to darken in color and appear shiny. As the problem carries on, leaves will start to change color and appear burnt with spots. Eventually the leaves will wilt and become crispy, causing them to be completely useless
How to Cure:
If your pH is already correct, you will need to add a phosphorous rich nutrient to your feeding schedule. Phosphorus is the P in N-P-K, so be sure to look on the nutrient label for something with a high ratio in the P section. Most Bloom related products will feature an abundant amount of this nutrient. This will include the Fox Farms Tiger Bloom and the General Organics Bio Thrive Bloom.