Do you Have Potassium Deficiency in your Marijuana Plants?

Burnt tips?

Yellow spots. Browning leaves.

If your lights and temperature levels are good, you could have potassium deficiency going on within your marijuana plants.

This could be bad news if it’s not fixed soon.

Lack of potassium can also be confused with other nutrient deficiencies like magnesium, or zinc (at the early stage ).

There is plenty of information here to help you make sure you know that you’re dealing with a potassium issue.

Let’s jump right in,

Signs of Potassium Deficiency

  • ​Stunted Growth
  • Moves from bottom of plant to top (Mobile nutrient)
  • Yellow or white spots on leaves
  • Yellow, Browning or blackening of leaf tips
  • Stems become weak and brittle
  • Space between branches may increase
  • May look like nutrient burn
  • Also, resembles heat stress
  • Yellow leaves (older) bottom
  • Leaves curl under


Lets quickly take a look at what potassium is and why it’s important to marijuana.

Potassium is an essential nutrient of marijuana and all living plants.

Without it, the plant will die.

It is a mobile nutrient and aids with photosynthesis and the movement of water and amino acids and creates ATP in the plant. According to the University of Minnesota.

Potassium also helps in the regulation of water to oxygen which converts to carbon dioxide within cannabis.

It’s important because when cannabis plants do not get enough water, potassium helps when in the drought stage.

It’s also good for plant immunity levels against disease and insects.


Potassium is letter K in the symbols that make up part of N-P-K that is on organic fertilizer bottles.

You will notice different levels of potassium for various stages of growth on many nutrients on the market.

N stands for Nitrogen

P stands for Phosphorus

K stands for Potassium

Vegetative Stage

During the vegetative stage, you will require less potassium and phosphorus, and need more nitrogen.

Nitrogen aids in early plant growth along with potassium to help with root growth.

Potassium deficiency in cannabis can occur during the vegetative stage but be sure to remember it could be other nutrient deficiencies as well.

Browning and yellowing of the leaves

Flowering Stage

For the flowering stage, you will need to increase the Potassium and Phosphorus levels.

Most blooming fertilizers out there do this automatically and just need to switch to the flowering stage in your nutrient schedule.

Potassium is beneficial for the flowering stage, which is essential for terpene production.

If not enough is provided during flowering your buds, it will lack flavor and smell!

You will most likely face more potassium deficient issues during the flowering stage.

Lower leaf showing late stage of potassium deficiency.

Causes of Potassium Deficiency

The causes of potassium deficiency in cannabis can be some factors, such as the buildup of salts in your growing medium (soil or coco coir).

If using hydroponic tubs or bins, this is far less likely to occur but is known to happen on occasion.

Make sure you have a good pump.

You can also run into Potassium Lockout.

Potassium Lockout happens when the PH is below a certain level.

This causes the medium to become acidic for the roots which stop’s the uptake of potassium by your plants.

Here are some PH values to watch for if they are below these values:

When growing in soil: PH levels of 4.0-5.5

Hydro and Soil Less Mediums: PH levels of 4.0-4.5

How to Fix Potassium Deficiency

The best ways to fix potassium deficiency with marijuana is:


Use organic or synthetic nutrients with properly balanced levels of N-P-K for veg or flower cycles.


Correct the PH level in water/ nutrients.

The optimal ranges should be in the following markers:

Soil, 6.0 – 6.5 pH range. Hydro or coco coir, 5.6 – 6.2 pH range


Use a PK booster


Incorporate a K booster


Add Wood Ash to the grow medium


Kelp meal is also an alternative you can add to the top of soil or coco. A little goes a long way. It’s slowly absorbed during feeding schedules.

After trying some of the solutions, you should be able to recover within a week.

However, the damaged leaves on your cannabis plants will not recover.

It is best to remove them when you start to see the deficiency start to take hold of your plant.

Working its way up the plant

PK Boosters for Marijuana:

Here are some of the popular PK boosters for your cannabis plants.

Botanicare Hydroplex Bloom contains the right amount of phosphorus and potassium. To help your plants out.

With essential amino acids. Hydroplex provides the right balance to enhance flower development and give denseness to your buds. 0-10-6 combination.

Canna PK 13/14 well you guessed this is one of the highest PK boosters on the market the name says it all.

Used by many growers to stimulate blooming and also enhances bud structure.

Humboldt Nutrients Ginormous is an ultimate pk booster with zero nitrogen and all phosphorus and potassium you need.

A bloom booster that is biodegradable and may boost your grow to the next level. The values are 0-18-16.

K Boosters for Marijuana:

Here are some of the popular K boosters for your cannabis plants.

Humboldt Deuce Deuce is very high in potassium, and sure to fix all your problems.

With all natural ingredients and comes in at a whopping 0-0-22. It also helps with growing massive but in flowering as well.

Seaweed Bliss Premium Seaweed extract is pack full of the best essential micronutrients for plants with over 70 of them.

This seaweed extract is harvested out of the U.S.A frigid coastal waters.

Seaweed bliss seaweed is great for seedling all the way to the flowering stage.

Providing root development and also bud development. Great for increasing your potassium levels in your cannabis plants

Signs of Excessive Potassium

  • New leaves show yellowing chlorosis.
  • Leaf tip show some sign of burning.
  • Lower leaves curl gets spots.
  • Blocks the absorption of other nutrients such as calcium, magnesium, zinc, and iron.
  • Grow medium becomes acidic lower than PH 5
excessive potassium marijuana

How to correct excess potassium

The best ways to fix excessive amounts of potassium in your cannabis plants is to try the following to repair the damage.


Flush your plants with water for a couple of feeding to try and clean the root structure.


Try and use some balanced nutrients.


Dial down your nutrient amounts as the guidelines from the companies are just that. Guidelines.

Some cannabis plants may need more nutes than others.

Final Thoughts

If you do come across potassium deficiency with your cannabis plants it’s easy to recover from when working with the right nutrients.

Sometimes you just have to flush the marijuana plant to get it to recover, then find the right balance of nutrients.

Add a PK or K booster if required.

Have you dealt with potassium issues and what worked for you?

Let me know in the comments !

Grow on my friends.

Image credits: image

4 thoughts on “Do you Have Potassium Deficiency in your Marijuana Plants?”

    • Don, That would depend on if you are already supplementing with K in your nutes. I would not add what they recommend on some of the Potassium additive lable , I would slowly add a little bit to see if my plants start to recover. Always start small so you don’t shock your plants. There is no one special formula.

  1. Hi Parker Lewis,

    I am in week8/9 of my winter grow – girls go undercover at night, days are nice 20c +. I found at first watering there was always water at the base of pots, now its every 3rd or 4th day.

    Bottom leaves seem yellow, could be N as i am using Canna 13/14 with baby doses at first 4ml each time I water instead of the 15ml /10L

    Tips seem to have burns right on the edge as seem in the video i made. Havent grown much, could be due to gnats i had to kill, and time of year. Lovely smelling at the moment with PineAppleExpress Auto GSC auto etc. especially when i left their cover in themorning ( 70% uv shade cloth)


    • In flower the leaves will turn a little green and start to yellow, due to lower nitrogen. It can also be not giving it enough nutes. And your gnats infestation might have stunted the growth.


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