How to Treat Cannabis Potassium Deficiency with Biostimulants

Potassium is an essential macronutrient for all plants. It is critical for plant growth, development, and metabolism, and it plays an especially interesting role in cannabis production.
Known as a quality element, potassium significantly influences the color, aroma, and bud size of cannabis crops. Prolonged potassium deficiency can reduce not only yields but these important subjective qualities as well. Improper potassium levels may even reduce concentrations of cannabinoids and terpenoids.
Potassium deficiencies are a common problem for cannabis growers, and although additional fertilization is the logical and often-taken course of action, it is not always the correct one. Addressing potassium deficiency should include exploring nutrient access, not just nutrient supply.
This blog will look at how biostimulants like microbial inoculants increase plant access to potassium and other nutrients already in the soil. Incorporating biostimulants into fertilizer programs can sustain yields, optimize crop quality, and improve soil health—all while reducing overall input requirements.
But to effectively apply biostimulant solutions to cannabis potassium deficiency, we first need to reliably identify the symptoms of this deficiency and understand potassium’s role in the growth and development of cannabis crops.

Symptoms of Cannabis Potassium Deficiency

Potassium—the K in NPK—is critical to the metabolic processes of all plants, including cannabis. It is one of the “Big 3” nutrients, alongside nitrogen (N) and phosphorus (P), that plants require in the highest quantities, and that every commercial fertilizer aims to provide.
But even with adequate fertilization, potassium deficiency can still present as an issue, depending on soil chemistry, moisture levels, and other abiotic conditions.

Cannabis potassium deficiency symptoms typically appear in the flowering stage. They can include:

● Yellow or brown leaves, usually—but not always—starting with the tips of the oldest leaves, before extending further in the leaves and upwards to newer growth.

● Weak, easily bendable stems.

● Delayed bud formation.

● Reduced resistance to drought and extreme temperatures. 

The first symptoms of potassium deficiency look similar to nutrient burn. But if the edges and insides of leaves increasingly turn yellow or brown, potassium deficiency is the likely culprit. 

Cannabis and Potassium’s Role

Potassium fuels growth and stress resilience by enabling the movement of nutrients, water, and carbohydrates throughout plant tissue. It catalyzes cannabis growth and development by:

● Helping to synthesize the proteins and amino acids delivered by nitrogen.

● Improving resilience to both biotic and abiotic stresses, like pests, drought, and frost.

● Increasing the strength and resilience of plant tissue and root systems.

● Activating growth-promoting enzymes.

● Improving plant morphology, thus increasing the weight, volume, and density of cannabis buds. 

Proper potassium levels also encourage the development of desirable aesthetic qualities in cannabis. Legal restrictions around the world have severely limited research on cannabis specifically, but potassium has long been identified as a “quality element” in food crops: it positively affects qualitative variables like fruit size, appearance, color, aroma, nutritional content, and shelf life. 

Recent studies demonstrated that potassium has a similar effect on the qualitative variables of cannabis, including bud size, color, and aroma. However, oversupply of potassium may decrease concentrations of cannabinoids and terpenoids. Finding a balance between deficiency and excess is important. 

Treating Potassium Deficiencies While Avoiding Excess Fertilization

Although prolonged potassium deficiency is a profound risk to crops, potassium excess is also an issue, especially for cannabis. Too little potassium, plant health suffers and yields drop. Too much, and cannabinoid and terpenoid levels may be negatively affected, potentially diminishing crop quality.

So, although added fertilization is sometimes necessary, it is helpful to understand the mechanisms of nutrient uptake before the addition of more potassium fertilizer to your growing medium.

Potassium is fixated in soils quite fast, but it is released—or made available to plants—slowly. As much as 90% of soil potassium may be unavailable to plants at any given time. Factors that can limit potassium availability include:

● Soil PH and chemical composition

● Extreme temperatures

● Excess magnesium

● Tillage systems

● Soil moisture and irrigation protocols

● The rhizosphere

A healthy rhizosphere, one replete with beneficial microbes, can moderate many of these variables to the plant’s benefit, increasing the bioavailability of potassium that would otherwise be “locked” in the soil.

Some soil bacteria and fungi are classified as potassium solubilizing microbes, or KSMs. They excrete organic acids that release potassium from minerals like illite, micas, and orthoclase. KSMs are the key to the potassium vault, unlocking it for plant uptake.

Most soils are rich in potassium. Expensive, environmentally damaging conventional fertilizers are often overapplied, and excess potassium can potentially even be detrimental to cannabis. In addition to appropriate fertilization programs, growers can treat deficiencies by leveraging the riches already in the soil—with the help of microbial inoculants and other plant biostimulants.

 Biostimulants are an effective and holistic way to treat potassium deficiency and promote healthy growth. Don't make your plants wait any longer- browse our online store here.



Treating Cannabis Potassium Deficiency with Plant Biostimulants

Microbial inoculants are classified as a plant biostimulant—any substance or product that stimulates biological processes to encourage plant growth and development. They are an easy way to introduce beneficial microbes to the rhizosphere. Other common biostimulants include amino acids, seaweed extracts, protein hydrolysates, and compost.

Microbial inoculants can be used in conjunction with any conventional fertilizer program to maximize plant uptake of potassium and other nutrients essential for cannabis plants, including nitrogen, phosphorus, calcium, magnesium, and sulfur.

Nutrient deficiencies are often treated by addressing the symptoms, not the cause. Causes can be multifaceted, defying a simple prognosis, but oversimplifying them risks long-term environmental and financial consequences.

Microbial inoculants help us approach the muti-faceted nature of complex horticultural problems more effectively. They provide growers with holistic solutions that simultaneously maximize yields, improve soil and plant health, and minimize environmental impacts by reducing fertilizer demand.

Microbial Inoculants for Cannabis Growers

Impello’s organic fertilizers and microbial inoculant amendments are designed to holistically address nutrient issues like cannabis potassium deficiency in all irrigation systems, media types, and growing environments.

Microbial inoculants, like our new Continuμm™ formulation, provide plant growth-promoting rhizobacteria (PGPR) that will improve nutrient availability while boosting root development, water uptake, and crop tolerance to abiotic stressors. Research focused specifically on beneficial microbes in cannabis production is still in its infancy, but early studies indicate that PGPR application can even positively impact CBD and THC content.

We’re passionate about making horticulture better, for growers and the planet. If you have any questions about microbial inoculants and biostimulants for cannabis production, we want to hear from you! For technical questions, please email us at For general questions or to place an order, email

For more on microbial inoculants and cannabis potassium deficiency, please see the references used to write this blog:

Bernstein, N., Gorelick, J., Zerahia, R., & Koch, S. (2019, June 17). Impact of N, P, K, and Humic Acid Supplementation on the Chemical Profile of Medical Cannabis (Cannabis sativaL). Frontiers in Plant Science, 10.

Meena, V. S., Bahadur, I., Maurya, B. R., Kumar, A., Meena, R. K., Meena, S. K., & Verma, J. P. (2016). Potassium-Solubilizing Microorganism in Evergreen Agriculture: An Overview. Potassium Solubilizing Microorganisms for Sustainable Agriculture, 1–20.

Saloner, A., & Bernstein, N. (2022, May 23). Effect of Potassium (K) Supply on Cannabinoids, Terpenoids and Plant Function in Medical Cannabis. Agronomy, 12(5), 1242.

Saloner, A., Sacks, M. M., & Bernstein, N. (2019, November 18). Response of Medical Cannabis (Cannabis sativa L.) Genotypes to K Supply Under Long Photoperiod. Frontiers in Plant Science, 10.

Usherwood, N. R. (2015, November 2). The Role of Potassium in Crop Quality. Potassium in Agriculture, 489–513.

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