Even for the experienced grower, nutrient deficiencies can be difficult to diagnose. So many nutrient deficiency symptoms overlap. I find that the best place to start is understanding the role of each nutrient in plant growth. Diagnosing potassium deficiency in cannabis is simplified if you know what roles potassium fulfills.
Potassium and Plant Growth
Potassium is reported as “K” on a nutrient label, or referend to as “potash”. This nutrient has three vital contributions to growth. The first is in nutrient, water, and sugar translocation in plants. Without sufficient potassium levels, transpiration will not occur and nutrients will not move from the roots to the shoots and developing buds. The second, it’s role in cell energy. The binding and severing of potassium from ATP stores and releases the energy required for proteins to function. Finally, stomata opening and closing are potassium regulated. These pores regulate the exchange of water vapor, oxygen, and carbon dioxide. Without these components, the plant would not grow. Other notable roles include:
- Increases root growth and improve drought resistance.
- Maintains turgor; reduces water loss and wilting.
- Aids in photosynthesis and food formation.
- Reduces unnecessary respiration, preventing energy losses.
- Enhances translocation of sugars and starch.
- Increases plants’ protein content.
- Builds cellulose and reduces lodging.
- Helps slow diseases.
Potassium Deficiency In Cannabis
Potassium deficiency reduces Transpiration. The evaporation of water off of the leaves (leaving the stomata) cools the leaf tissue. When this doesn’t occur, the leaves will get too hot and cells will burn. This occurs mostly on the edges of the leaves. The margins, where normally evaporation is the highest, will scorch and brown.
Potassium is an immobile nutrient. This means that when there are deficiencies, you see them in the new growth, the tips of the plant. When nutrients are mobile, the plant will pull from old tissue and send it to new tissue to grow. With immobile nutrients like potassium, the deficiency appears in the new growth. Tips of leaves will curl up radically and eventually drop off. The deficiency will reduce flowering and substantially decrease yield.
Potassium In Your Media
Potassium deficiency is the result of media issues. Foliar potassium fertilization is unrecommended. Often, deficiencies are caused by too little, or the wrong type of fertilizer. Since potassium is found in 3 forms, only fertilize with readily available potassium. Some potting mixes bind potassium, blocking absorption by the roots. Adjusting the pH of your nutrient solution to a neutral range will help solubilize potassium. Coincidentally, most “pH up” formulations utilize potassium. Potassium Hydroxide raises the pH and plants uptake it as food.
Potassium problems can also be the result of excess sodium in the root environment. Sodium slows down potassium intake. Flush the media with a nutrient-free (but still buffered) solution to rinse out extra salts.
When fertilizing with potassium, Langbeinite, greensand, and seaweed are all organic forms. Potassium is also a component in compost and manure. Other nutrient formulations will contain K20 (potash) potassium chloride (KCl) or potassium sulfide (K2SO4).
Real Examples of Potassium Deficiency
The gallery below shows many photos of potassium deficiency in plants. If you are still having trouble identifying nutrient deficiencies, reach out to a cannabis consultant for help.
