Potassium Deficiency In Marijuana

Potassium deficiency is one of the most common marijuana deficiencies. Symptoms generally appear when the plant enters its flowering stage. 

You shouldn’t worry if you only see one or two leaves with yellowing. If, however, you see the problem progressing, take a look at some of the solutions listed below.

How To Identify A Potassium Deficiency

cannabis-potassium-deficiency-color-chartThere are several ways in which a potassium deficiency manifests, and they’re not necessarily similar to each other. In fact, the problem is often confused with nutrient burn or other deficiencies.

In Lower And Middle Leaves

One of the most commonly visible symptoms is when the leaves turn yellow, beginning at the tips and gradually advancing towards the base.

The “burn” of the edges and tips of the leaves is another of the common symptoms. Since potassium is essential in the regulation of temperature, the leaves do not regulate correctly and appear burned. These burns can resemble nute burn.

The distinction here with the symptoms of nutrient burn is that the potassium burn will be limited to the tips. With the lack of potassium, the burn will also show on the edges, and in a short time it will be accompanied by minimal yellowing.

Depending on your case, you may see the yellowing or “burns” first. If these advance, the leaf will continue to lose color and burn, and spots of dead tissue will appear, until it wrinkles and dies.

If you find red, brown, or gray spots on the stem, a potassium deficiency may also be the cause.

In Upper Leaves and Shoots

Sometimes you will see these symptoms on upper leaves. Potassium moves freely around the plant and it will eventually show up in upper leaves.

If the deficiency becomes severe, you will notice that your plant has slowed its growth. The new shoots will not grow as fast and their leaves will be smaller compared to the old ones.

How Does The Lack Of Potassium Affects The Buds?

Potassium deficiency delays bud formation, and decreases bud size, weight and density. If the plant lacks potassium in its flowering stage, you will have skinny and poorly developed flowers.

The other essential nutrient for the flowering stage is phosphorus, and commercial fertilizers for flora are loaded mainly with potassium and phosphorus.

Potassium Deficiency Symptoms

SymptomsLeaf Color
Slowed growthOld leaves take on a strong yellow hue
Leaf tips dieTips get “burned”
Stretching (plant grows too tall)Edges get “burned”
Decreases bud size and densityRed, brown, or gray spots on the stem (less common)

Evolution Of Potassium Deficiency And Pictures

If this don't look like your leaves, you can compare with pictures of other marijuana leaf symptoms and how-to guides.

What Does Cannabis Use Potassium For?

Potassium is one of the three main components that make cannabis plants thrive, specially when they're flowering.

Potassium helps with the movement of water, nutrients and carbohydrates in plant tissue. It’s involved with protein, starch and adenosine triphosphate (ATP) production. The production of ATP can regulate the rate of photosynthesis.

Potassium In The Vegetative And Flowering Stages

From the beginning, potassium is necessary for the plant to grow strong, develop the stem well, and improve its resistance to cold and disease. It also helps essential functions such as temperature regulation and respiration.

This deficiency can cause your plant a lot of problems. Among them are slow growth, low production of buds, or skinny buds that fail to gain weight despite maturing.

According to Extension, at the University of Minnesota, other roles of potassium are:

Increases root growth and improves drought resistance Maintains turgor; reduces water loss and wilting
Aids in photosynthesis Reduces respiration, preventing energy losses.
Enhances translocation of sugars and starch Helps retard diseases.
Increases plants’ protein content. Builds cellulose and reduces lodging.

Causes Of Potassium Deficiency

The main cause of a potassium deficiency is the lack of potassium in the growing medium.  Make sure to start your plants packed up with nutrients so all goes well while the plant is growing.

If you're seeing this deficiency, your plants are most likely are asking for more food. Especially if they are flowering.

If, instead, you're sure you gave them enough potassium, there are other reasons the plant is not taking it up.


From transplants, poorly done pruning, or too much heat can cause a potassium deficiency. If this is the case, the plants will be back to after a few days. Keep taking care of her and don't over-do things.

PH Variation

PH variation of the irrigation water or your substrate. If the pH of the substrate is outside the range, the roots will not be able to absorb potassium, however much is available.

  • In Soil: PH of 6.0 to 7.0
  • Hydro And Soil Less: PH of 5.5 to 6.5

Check this guide from Dinafem seed bank on how to regulate pH in different growing mediums.

Excess Salts

An accumulation of salts in the roots in the growing medium (soil or coco coir) will also impair the absorption of potassium. In this case, you can flush the root system with the cleanest water possible.

With hydroponics, this is less likely to occur but is known to have happened. Make sure you have a good pump.

A Light Burn 

Light burns can form spots similar to potassium deficiency. It’s hard to hit the sun, but if you have an indoor setup, is it possible that the light is too close or the light has too much power. Your plants can withstand a good amount of light, but they do have limits.

How To Fix Potassium Deficiency

If are already fertilizing the substrate, you should not have any of these symptoms. So, before solving the problem you have to find out the reason for the lack of potassium. I previously listed other causes that can lead to a potassium deficiency, even if there are enough nutrients.

If you’re not giving your plants enough fertilizer, check out the sections below.

Bloom Boosters!

The easiest and safest way to correct the problem is to buy bloom booster fertilizer. You can get it online, in a growshop or nursery.

Jack's Classic Blossom Booster Fertilizer

Jack's Classic Blossom Booster Fertilizer is a highly effective and affordable option for growers looking to boost their flower production and overall plant health. While some users have reported a strong odor, the fertilizer is generally considered easy to use, coming in a convenient powder form. This product seems to be popular among budget-conscious growers who are looking for a simple and effective fertilizer for their plants.

Jack's Classic Blossom Booster

FoxFarm Tiger Bloom Fertilizer

FoxFarm Tiger Bloom Fertilizer is a must-have for indoor and outdoor growers looking for an effective fertilizer for the flowering stage of their plants. This versatile liquid fertilizer is easy to mix and apply and has a reputation for delivering impressive results. Some customers find it to be a bit pricey and may not like the strong odor. Despite these drawbacks, many happy customers highly recommend this fertilizer for its overall effectiveness.

FoxFarm Tiger Bloom Fertilizer
FoxFarm Tiger Bloom Fertilizer

General Hydroponics FloraBloom

Maximize your blooms with General Hydroponics FloraBloom Fertilizer. Known for promoting vigorous flowering and producing larger blooms, this fertilizer is easy to use and contains all the necessary micronutrients for optimal growth. Some users have reported inconsistent results, but many have found success with this product. Despite its high price point compared to other fertilizers, it's worth the investment for those who want to achieve stunning results.

General Hydroponics FloraBloom Fertilizer
General Hydroponics FloraBloom Fertilizer

How much Bloom Fertilizers do I need to fix a Potassium Deficiency?

That would depend on if you are already supplementing with potassium. And also on the brand that you choose. Carefully read the label and instructions of the package. Check comments online for that specific brand. And always start small and go from there.

Banana Peel Tea: Homemade Potassium

Homemade fertilizer is also an option that’s discussed in cultivation groups. It’s not only used to solve deficiencies but also to fatten buds during flowering.

You’ll find plenty of potassium and phosphorus, the key nutrients in flowering, in the peel of a banana, and the banana itself if it is ripe.

True banana tea is actually a cold tea, despite the fact that most people usually boils it.

If you banana peels to soak in water for enough days, it will begin to pass its nutrients to it thanks to the formation of bacteria. Otherwise, if you boil it, you will not get as many nutrients and many will be lost due to high temperatures.

How To Make Banana Peel Tea

  1. Let the water sit for at least 24 hours to clean it,
  2. Cut the banana peels into pieces,
  3. Put the pieces in a jar filling about 5 centimeters,
  4. Finish filling up to 3/4 of the total content with water,
  5. Cover it with a rag,
  6. Let it rest in the fridge for 3-5 days,
  7. Stir it a couple of times a day,

Note: Gasses in the jar are normal. However, if you see any type of mold accumulation, you must start again. The tea should smell sweet and of banana. If it has an acid or rancid odor, do not use it, try again, leaving it for fewer days.

step-2-banana-peel-tea-marijuana-potassium-floweringAfter a few days, all that's left is to strain it — so as not to leave food scraps on the soil.

To water, first you must dilute the tea in standing water, 1 liter of water for every half glass of tea — or 1 part of tea for every 10 parts of water. Then water your plants normally. This banana tea will provide your plant with significant amounts of potassium and phosphorous, as well as other beneficial microorganisms for the substrate.

This will provide your plant with significant amounts of potassium and phosphorous, as well as beneficial microorganisms for the substrate.

Don’t apply it too often. Depending on the size of your plant, applying it to the irrigation water once every week will be enough. It is important to never overdo your fertilizers; it’s better to apply a little many times than a lot once and overdo it.

Wood Ash

Wood ash is a touchy subject; I recommend it only if you grow outdoors directly on the ground. For pots it is preferable to use another method like those I specified above.

If you start to sprinkle ash on the soil during the first weeks of flowering, you will provide your plants with excellent levels of potassium. But you must be careful: wet ash will generate lime and salt that in large quantities can burn the roots or modify your pH levels, which can generate deficiencies.

How To Use Wood Ash:

Start the plant slowly, using a little ash and see how it reacts, then increase the dose.

  1. If you have a stove or grill, collect the finest ash you can find in a plastic bag, leaving aside the pieces of coal,
  2. Take a handful and sprinkle around the plants above the ground, without touching leaves or flowers,
  3. Take care not to cover all the soil. Take a look at the example photo.
  4. Water normally with standing water from now on.
Wood ash fertlizer
Wood ash fertlizer

This will give your plants a good shot of potassium, and it will stay in the soil and distribute nutrients for a while.

Be very careful not to sprinkle too much. If you are applying this type of fertilizer, you should begin regulating the soil pH.

Bone Meal

Another method is to add bone meal, if you feel comfortable with fertilizing and maintaining the pH of the substrate. You can buy it in any nursery and apply it in the same way you would apply ash.

Bone meal is a fertilizer that absorbs slowly, so your plant will be ready to continue absorbing after recovering.

With bone meal you will get a great amount of phosphorous, potassium, calcium, and magnesium. Ideally, you should use it when you assemble the substrate so that it is present throughout the process.

Bonea meal fertlizer
Bone meal fertilizer

Final Thoughts On Potassium Deficiency

Fortunately it's easy to recover from a potassium deficiency with cannabis plants. After adding PK booster or organic fertilizer, in a week or so you show see signs of recovery.

If after adding potassium your plant doesn't recover, read above "other causes" and deeply investigate your growing medium, levels and routines to try to figure it out.

Sometimes you just have to flush the roots and start over, then create the right balance of pH and nutrients.

Hey there, I'm the person behind this website. I started growing cannabis in 2014 right after marijuana was legalized in my home country. Today, on drcannabis.io, I address growers need for knowledge and show you how to grow cannabis plants and enjoy amazing buds.

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