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David Rhodes

David has been working in the cannabis industry for the past 17 years with experience working overseas in Amsterdam as a budtender for 5 years! Learn More About David!

Most Recent Update January 23, 2023: Cultivating cannabis can either be a simple process or somewhat exasperating. Observing the healthy growth of your cannabis plant can bring a sense of satisfaction. However, insufficiencies in marijuana plants can potentially thwart your endeavors, leading to a host of issues.

Potassium Deficiency In Cannabis Plants

The most common deficiency in marijuana is potassium. Many people confuse potassium deficiency in marijuana with other nutrient deficiencies such as zinc or magnesium, nitrogen, at least at the initial stages.

potassium deficiency in Marijuana

Lack of potassium could be detrimental as it plays a significant role in the general health of your cannabis plant. Potassium is an essential nutrient that contributes to different metabolic processes, growth, and morphology.

It is a crucial component in both responses and defense to biotic and abiotic stress or pest. The nature of its role in assisting plant growth and stress is centered around its effectiveness in affecting nutrient uptake, cell membrane osmosis, and stomata dilation.

When it comes to marijuana, often, issues related to potassium are deficiencies. Potassium toxicity in this plant is less or more an issue of inhibition or antagonism of other nutrients.

potassium deficiency in weed plants

Indications of potassium deficiencies usually begin in older leaves. The edges of the leaves turn yellow or brown. Additionally, they might look like they’re burned eventually causing the leaf margins to change to yellow then brown, and finally die.

How To Fix Potassium Deficiency In Cannabis

A potential potassium deficiency in marijuana might be from several sources as already mentioned above. While one or several leaves might be fine, you’ll need to do damage control if you observe the movement of damaged leaves is drastic and lethal (more yellowing, and dead parts of leaves finding their way below and center part of the leaf), then it is time for major remedying of the situation.

Combat potassium deficiency in marijuana plants through these strategies;

Use Good Sources of Nutrients

Potassium is usually deficient in certain conditions. These include the use of reverse osmosis or heavily filtered water.

The two methods of feeding marijuana plants lead to potassium deficiency. However, the use of friendly nutrients will supply adequate potassium.

The golden rule is to utilize synthetic or organic nutrients that boast properly balanced N-P-K levels for flower and vegetative cycles.

Adjust the PH Accordingly

Of great importance to note is that potassium is absorbed better at lower pH ranges. When it gets too high, the plant exhibit signs of mineral deficiency.

Always correct the pH levels in both nutrients and water.

Flush the System

If you suspect that the leaves are suffering from potassium deficiency, flush the system using pH’d water that features an appropriate dose of marijuana-friendly nutrients.

If the damage is too old and has severely affected the plant, chances of this strategy working are next to impossible.

Ensure It Is Potassium Deficiency, Not Light Burn

Whenever marijuana plants grow too close to their source of light, the leaves can get light burn which almost resembles potassium deficiency. Therefore, when looking for a sign of potassium deficiency, be sure it is not a light burn.

The main difference between these two types of burn is that the one that is caused by nutrient deficiency is not only restricted to the tips but also edges. Within a short time, it is coupled with yellowing although in minimal spots of the leaves.

The rule of thumb when determining the distance to set between the plant and light is around 12 inches or 30 centimeters.


You can correct potassium deficiency using other strategies such as:

  1. Consider using a PK booster. Popular and effective PK boosters for cannabis plants include Botanicare Hydroplex Bloom, Canna PK 13/14, and Humboldt Nutrients Ginormous.
  2. Consider incorporating a K booster. Some of the efficient K boosters for marijuana are Humboldt Deuce Deuce and Seaweed Bliss Premium Seaweed.
  3. Consider adding water ash into the growth medium

Note: Once you apply the above strategies of combating potassium deficiency in marijuana, you should enjoy results in terms of plant recovery. Nonetheless, if the leaves were severely damaged, chances of recovery are almost zero. The prudent thing to do in such a case is to remove them once you begin to observe the deficiency taking hold of the plant.

Functions Of Potassium In Cannabis Plants

Potassium is an important nutrient in all plants, not only cannabis. Without it, plants die.

This mobile mineral aids with a host of processes. For instance, it helps with the movement of amino acids and water. Additionally, it creates ATP in a plant.

It regulates water into oxygen which then transforms into carbon dioxide in the plant. If your plants do not have adequate water, the nutrient plays some of the roles water does.

Potassium is effective at boosting the immunity of plants against insects and diseases.

Chiefly, potassium acts as a catalyst in metabolic processes. In summary, these are some of the functions of potassium in cannabis plants;

  • Improves density, weight, and volume of buds.
  • Acts on plant sap increasing frost resistance.
  • Combines with phosphorus to boost resistance and strength in roots.
  • Strengthens and ensures consistency of plant tissues.
  • Enables plants to survive drought periods.
  • Takes part in the synthesis of amino acids and proteins.
  • Interacts with nitrogen to perform other metabolic processes.
  • Plays a role in photosynthesis by speeding up carbohydrate synthesis.

Potassium In Different Stages Of Cannabis Plant Growth

As aforementioned, potassium plays different roles when it comes to the growth of the cannabis plant. Of great importance to note is that the nutrient is letter K in symbols that constitute N-P-K (nitrogen, phosphorus, and potassium) on the organic fertilizer bottles.

For different stages of growth, you’ll notice various levels of the nutrient. The different stages are:

  • Vegetative stage
  • Flowering stage

Vegetative stage

In the vegetative stage, plants need less phosphorus and potassium, and more nitrogen. Nitrogen coupled with potassium aids in plant growth especially the roots.

Although potassium deficiency might occur in the cannabis plant during this stage, be sure to check for other nutrient deficiencies as well.

Flowering stage

When it comes to the flowering stage, you’ll require an increase in phosphorus and potassium levels. Potassium is highly beneficial at this stage for its role in the production of a terpene.

If the nutrient is minimal or lacks entirely at this stage, then it’ll lack smell and flavor.

Potassium deficiency issues are highly likely to occur during the flowering stage of your cannabis plant.

Signs Of A Potassium Deficiency

Marijuana plants growing in a hydroponic system rarely suffer potassium deficiencies. A close observation of any symptom (s) could reveal it is a result of other issues but not potassium deficiency.

Plants that suffer potassium deficiency are easy to identify. Mostly, the plant will have an elongated and weak stem. Another common indicator is the color of the leaves. Necrotic spots and brown to tan-colored leaves indicate a potassium deficiency.

potassium deficiency in marijuana

The leaves change to yellow, starting on their tips and slowly progressing towards the base. Additionally, you’ll also notice that the tips and edges of the leaves ‘burn’ as the nutrient plays a big role in temperature regulation.

In summary, the signs of potassium deficiency include;

  • Slow growth and development rates which in turn affects yields
  • High susceptibility to diseases and pest
  • Increase in space between branches
  • Weak and brittle stems
  • Leaf curling
  • Weakened and curled petioles on the leaves
  • Leaf tips turn black, yellow, or brown
  • Tips of older leaves turn yellow inwards from the tips
  • Leaves have yellow or white spots
  • Growth is generally stunted

Some signs of excess potassium include;

  • Growth medium becoming acidic (reduces to lower pH of 5)
  • Blockage of absorption of other nutrients such as iron, zinc, magnesium, and calcium
  • Lower leaves curl and get spots
  • Burning of leaf tips
  • Yellow chlorosis on new leaves

Note: You can fix excess amounts of potassium in your cannabis by doing the following:

  • Flushing the plants with water for several feedings to clean the root structure
  • Use balanced nutrients
  • Dial down nutrient amounts. (some plants need more than others)

Causes of Potassium Deficiency in Marijuana

Potassium deficiency may be caused by several reasons. Common ones include nutrient binding, nutrient antagonism, media imbalance, and stress. Upon noticing the first symptom, check for damage migration in the plant. That is simply the symptoms moving from one leaf to another.

Damage migration calls for corrective measures to be taken.

If you’re growing your marijuana in hydroponic bins or tubs, potassium deficiency is least likely to be caused by salt buildup in the growing medium. It can happen only occasionally.

Another cause of potassium deficiency can be what is known as potassium lockout. It occurs whenever the pH level reduces to a certain level.

When such a thing happens, the medium becomes acidic for the roots meaning there’ll be minimal potassium uptake by the plants.

If you’re growing your marijuana plant in soil, the pH level should be between 4 and 5.5. if growing in soil-less mediums and hydro, the levels should be between 4 and 4.5.

Relationship Between Potassium and Water In Cannabis

Water enters the roots through the process of osmosis. It then moves upward through the roots by capillary action. The process of water absorption is made possible by water loss in plants.

Leaves lose water to the atmosphere through the stomata. These are structures found on the leaf surface. Stomata can open and close through potassium ions which are either pumped in or out of guard cells. Guard cells are found in the stomata.

When potassium ions are pumped in guard cells, water moves in causing the stomata to open up. In turn, the open stomata acquire carbon dioxide for the process of photosynthesis. This usually happens during the day when there is light.

At night, potassium ions are pumped out of the guard cells causing the guard cells to lose water making the stomata close.

In plants that suffer potassium deficiency, this process takes hours giving a clear indication of how much water stress the plants undergo. Potassium is an important nutrient for plants to survive drought or dry periods.

In short, potassium when pumped in causes the stomata to open. When this happens the plant acquires carbon dioxide for photosynthesis. When water is scarce or there is darkness the stomata close. This happens when potassium is pumped out.

Without potassium, it is difficult for the stomata to function. Incomplete or slow stomata response causes stress on the plant especially when water is in limited supply.

Final Words

Potassium deficiency is common in marijuana plants. As a grower, you shouldn’t panic when you observe such an occurrence. If you notice browning leaves, yellow spots, or burnt tips, it could be an indication of minimal potassium levels. This is especially true if the temperature and light levels are good.

Early diagnosis and acting go miles to prevent the spread of effects. Waiting until it is too late to correct the deficiency will cause severe damage and in grave cases, death of the plant.

I hope you’ve enjoyed this guide on how to fix potassium deficiency in cannabis plants!



About David Rhodes

David has been working in the cannabis industry for the past 17 years with experience working overseas in Amsterdam as a budtender for 5 years! His goal is to help you with your cannabis grow! Learn More About David!

David Rhodes