Potassium (K) is one of a few essential macronutrients that cannabis plants need to survive and it plays an important role in many key biological processes. Without sufficient potassium, cannabis plants won’t be able to grow strong enough to produce high-quality flowers with good flavor and big yields.
In this comprehensive guide, we will show you how to identify, prevent, and treat potassium deficiency in your cannabis plants so you’ll be better prepared to advance as a grower.
(K) Potassium: Necessary for protein synthesis, hardiness, root growth, and the production of sugar and starch in the cannabis plant.
Macronutrient: Absorbed in large quantities from the growing media or the nutrient solution. Macronutrients are the best-known and recognized constituents of plant food and their potency is identified as N-P-K ratings, printed on all commercially available plant food containers.
Why is potassium important for cannabis plants?
So what does potassium do for plants? Potassium is necessary for a variety of biological processes in cannabis plants and it is especially important for photosynthesis, cell division, nutrient transportation and stress resistance.
Its primary functions include the following;
- Photosynthesis – Potassium helps regulate the opening and closing of stomata which controls gas exchange and water loss. This ensures efficient photosynthesis and overall plant health.
- Protein synthesis – Potassium is essential for the synthesis of proteins and the activation of various enzymes that promote proper growth and development.
- Sugar & starch production – Potassium is needed in order for your plants to manufacture sugars and starches that ultimately improve terpene production and overall bud flavor.
- Cell division & expansion – Potassium plays a critical role in cell division and elongation, directly influencing plant growth and biomass accumulation including flowering and fruiting.
- Nutrient transport – Potassium helps transport other essential nutrients within the plant, ensuring their proper distribution and availability of other key macro and micronutrients.
- Stress resistance – Adequate potassium levels improve a plant’s resilience to disease, pests, fungus, and abiotic stresses such as drought or temperature fluctuations (learn more here).
How do you identify a marijuana potassium deficiency?
Recognizing the early signs and symptoms of potassium deficiency in cannabis plants is crucial for all growers so you can start treatment as quickly as possible. Some common potassium deficiency symptoms that you need to look out for are;
- Yellowing or browning of leaf edges – Potassium deficiency often begins with the yellowing or browning of leaf edges, especially on older leaves. This can progress to necrosis and leaf death, seen as brown spots on the leaves, if not addressed.
- Curling or twisting of leaves – Leaves may curl or twist inwards, eventually becoming necrotic and brittle.
- Weak stems – Potassium-deficient plants may exhibit weak, slender stems that are unable to support the plant’s weight.
- Slow growth and reduced yields – Potassium deficiency can negatively impact overall plant growth, resulting in reduced yields and poor bud development.
Don’t misdiagnose a potassium deficiency in cannabis
Before diagnosing a potassium deficiency (or other nutrient deficiency), ensure that your plants are not experiencing light burn, nutrient lockout or nutrient burn. Yellowing leaves is a common symptom of many potential issues so proper diagnosing is needed before deciding it’s a potassium deficiency.
Light burn occurs when plants receive excessive light which causes bleaching or yellowing of leaves that looks similar to that of a potassium deficiency.
To differentiate between light burn and potassium deficiency you need to look at the location of the affected leaves. Light burn typically affects the upper leaves closest to the light source, while potassium deficiency usually shows up in older leaves, lower down on the plant.
Nutrient burn happens when the plant absorbs too many excess nutrients from the substrate resulting in overfeeding. At first, this will make the leaves get darker than usual in color before slowly getting burnt (yellow and brown) tips that start curling inwards. For novice growers, it’s easy to get confused if you have nutrient burn or potassium deficiency.
Nutrient lock happens when the substrate has enough nutrients but the plant is unable to receive nutrients and in essence get underfed even though the nutes are present. The symptoms of nutrient lock are stunted growth, yellowing or browning leaf tips and weak leaves and stems. More about how to treat nutrient lockout here.
Causes of cannabis potassium deficiency
There are several factors that contribute to potassium deficiency in cannabis plants. Learn them before you get started so you minimize the risk of damaging your yield.
- Not enough potassium in the growing medium – It may sound obvious but a lack of available potassium in the soil or hydroponic solution is the number one reason plants suffer from potassium deficiency. Inexperienced growers often underestimate the amount of potassium cannabis plants need and consequently underfeed them. Follow nutrient instructions closely and use easy-to-use systems like Flower Republic.
- Improper pH levels – Cannabis plants absorb potassium most efficiently when the growing medium has a pH between 6.0 and 7.0 (slightly lower for hydroponics 5.5-6.5). Outside of this range, potassium uptake starts to be impaired, and even though the potassium in the substrate is sufficient, the plant is not able to make use of it.
- Overwatering – Excessive watering can lead to “nutrient leaching”, reducing the availability of potassium in the growing medium.
- Competition with other nutrients – Overfeeding of plants can result in “nutrient lock”. High levels of calcium (Ca), magnesium (Mg), or sodium (Na) can interfere with potassium uptake resulting in a deficiency.
How to fix potassium deficiency in weed plants
After you have diagnosed your plants and decided that it is in fact a potassium deficiency that you are dealing with, you need to take steps to correct it.
Unfortunately, older damaged leaves, flowers, and branches won’t fully recover but observe new growth very carefully for several days after following the steps below. Make sure that new growth shows no signs of potassium deficiency and take notes so you learn for next time.
The issue should be completely resolved within four to seven days if you follow the steps below.
- Check and adjust the pH – Ensure that the pH of your growing medium falls within the optimal range for potassium uptake (6.0-7.0). The system needs to be flushed completely with clean pH water then add a balanced nutrient mix added back in.
- Add potassium-rich fertilizers – Introduce potassium-rich fertilizers, such as potassium sulfate or potassium nitrate, to the growing medium. For organic growers, options include compost, kelp meal, or wood ash.
- Monitor and balance other nutrients – Ensure that other nutrients are not competing with potassium by maintaining a proper balance in your nutrient solution or soil. You should regularly test your growing medium throughout the cycle to ensure optimal nutrient levels.
Potassium deficiency during the vegetative stage
Potassium deficiency during the vegetative stage can significantly affect your cannabis plants’ overall health and development.
In the vegetative stage, plants require a lot of potassium for root growth, cell division, and stress resistance. Addressing potassium deficiency during the vegetative stage is critical to prevent long-term consequences that may reduce yield and bud quality. It is generally easier to correct a deficiency at this stage than during flowering, so take the chance to perfect the environment for your plants.
Potassium deficiency during the flowering stage
During the flowering stage, potassium plays a pivotal role in bud development and the production of terpenes and cannabinoids. A deficiency during the flower stage results in reduced yield, lower potency, worse flavors, and overall poor bud quality (bunk weed).
- Gradually increase potassium levels – As your plants transition from the vegetative to the flowering stage, adjust your nutrient solution or add soil amendments to provide higher potassium levels. This will help support the increased demand for potassium during bud development. Use our simple 2-part nutrient solution and supplement with BudTone:PK as needed.
- Be vigilant for signs of deficiency – Regularly inspect your plants for signs of potassium deficiency. Prompt action can help mitigate any negative impacts on yield and quality.
- Maintain optimal environmental conditions – Stressful growing conditions can exacerbate potassium deficiency during the flowering stage. Ensure that your plants receive adequate light, proper humidity, and appropriate temperatures to support optimal growth and nutrient uptake.