Dealing with Potassium Deficiency in Cannabis Plants

Cannabis Potassium Deficiency
December 10, 2020

Potassium is one of the most important nutrients for cannabis plant growth, alongside nitrogen and phosphorous, potassium makes up part of the NPK ratio seen on most nutrient bottles. All three of these nutrients are required in high amounts during the vegetative stage which lessens as your plants enter the flowering stage. We have a great guide on How to Mix Nutrients which should give you a better idea of everything that is required, generally, and how to get the perfect ratios.

Having a nitrogen deficiency or phosphorous deficiency can be extremely detrimental to your plants overall growth and the same goes for a potassium deficiency. When it comes to potassium deficiency, cannabis plants display some telltale signs.

How to Spot a Potassium Deficiency in your Cannabis Plants?

Potassium deficiency, or potassium toxicity, will show itself in several stages. The first stage will be mostly dark green leaves with yellowing towards the center of the leaves or leaf it’s developing in. You may also notice small chlorotic spots or yellowing tissue due to the lack of chlorophyll. The second stage is going to be increased yellowing in the center as well as the tip or edge burning along with chlorotic spots will appear.

The leaf tip burning will mimic nutrient burn, however, potassium deficiency produces the same burn with a key difference being the yellowing of the leaves with the chlorotic spots. The final stages of potassium deficiency in cannabis would be dead, dying, or browning leaf tips with the majority of the leaves or leaf yellowing. Multiple chlorotic spots will develop and after prolonged periods of unresolved potassium deficiency, cannabis leaves will tend to shrivel up and die.

What can Cause Potassium Deficiency?

Several key mistakes can cause potassium deficiency as well as forms of stress training. Overwatering can be a cause of potassium deficiency, if you continuously flush your grow medium of water you are ridding it of nutrients as well, which will cause your plant to be unable to uptake what it needs to grow. You’ll notice deficiencies start to develop over time, potentially a potassium deficiency. PH range imbalances can be a serious problem for many growers.

For soil, we always recommend staying within 6.0 to 6.3 PH during flowering phases (we say flowering as cannabis uses more potassium during flowering) to utilize the proper zones for uptaking a solid distribution of flowering macronutrients and micronutrients, to make sure that some of the lower end micronutrients don’t get focused on absorption.

The flowering phase generally tends to be where most potassium deficiencies arise. However, if you notice when you are in the vegetative growth phase that you have a potassium deficiency, adjust your PH to 5.6 to 5.8 and you should see a nice healthy adjustment in the new growth of your plants.  This way you can utilize PK (potassium and phosphorus) to the fullest through the entire grow in all growth phases.

Another key mistake can be nutrient toxicity (lockup) or not enough nutrients. With this mistake, the fix is simply amending potassium into your regiment in higher doses if your plant is seeking potassium. That’s a simple way to handle that type of potassium deficiency treatment in plants.

Now, if your plant is locked out or showing chlorotic spots, that’s a good sign you’re just out of the proper PH range, or you’ve fed too much potassium. So we recommend flushing your plants with water that is PHed down to between 5.6 and 5.8 to allow any excess nutrient buildup to be flushed out. Do this 2 to 3 days in a row, then allow your grow medium to fully dry. Once dry give an adjusted feeding at the proper PH range, backing off on an excess of potassium until you have dialed in the proper dosage. It’s always best to feed less, as your plants will happily uptake more food on the next feed. It’s always a lengthier process to have to flush out excess nutrients, so keep that in mind.

What does Potassium do for Cannabis?

Potassium is directly associated with its macronutrient partner-in-crime, phosphorus. I mention this as to understand potassium’s role within cannabis plants, we also need to understand it’s connection or relationship with phosphorus. Phosphorus is a member of the macromolecules known as phospholipids, which are fatty acids composed in a chain-like manner that have attached to phosphate-substituted sugar. Due to this entire relationship, this creates a lipid bilayer that allows calcium to bind to it which through iconic balance and homeostasis these molecules are able to be drawn up in the water, through the roots.

So what does potassium do for cannabis? The major key role it plays is that it acts as the major ion promoting water flow into roots. So why does that matter? Without a mediator to assist nutrient acquisition, as Emanuel Epstein found out while researching Michaelis-Menten’s principals, plants cannot uptake nutrients. So it’s very vital there is a major ion promoting water flow into the roots as macro and micronutrients attach themselves in different bonding processes, or ionization, to different lipids which allows them to flow into the roots through the water molecules they now reside in.

Thanks to Emanuel Epstein and Michaelis-Menten we were able to identify countless membrane-bound proteins that are directly responsible for transporting ions from the root zone to root tissues. Basically, with their studies and many years of research we were able to determine directly how nutrients concentrate in specific pathways within the plant structure itself. From root tissue to leaf tissue and even stem or bud development. So with all that understanding, we see how vital it is for water to be drawn up by the roots, so to answer the question, what does potassium do for plants? Well, to put it simply, it allows them to consume their food to be able to grow and produce chemical reactions vital to growth or development.

How to Fix Potassium Deficiency in Soil?

If you are growing in soil or living soil you could potentially face potassium deficiency in several ways. First, if you are growing organically, potassium is already in low abundance within most organic soils, living soils, or nutrient formulas. Generally, this is why we recommend having a specific nutrient or amendment to feed or top feed your soil with, essentially feeding your plants! Bone meal is a great source for top feeding soil for those who like dry amendments. You can also add it to a tea bag in a compost tea. It’s high in potassium and phosphorus, with trace amounts of nitrogen. It does have some additional trace amounts of micronutrients, however, they won’t make an impact within your plant.

Bone Meal is predominantly PK heavy. You can also choose to add a liquid amendment into a compost tea or water feeding that specifically for potassium. Another way to organically add PK to your feed would be to use natural acids for adjusting PH imbalances. We recommend using potassium hydroxide for pH Up and phosphoric acid for pH down. However, keep in mind these natural acids are exactly that, acids. Please use extreme caution when working with them. They can and will burn your skin. These acids can add large amounts of PK to reservoirs or feeds so it’s best to use a little to start.

Now, another problem you could face is having too much potassium stuck within your grow medium. So this is a simple fix, it just takes a little patience and time. You will want to make a water feeding, regardless of what growth phase you’re in, PHed to 5.6 to 5.8 to help readjust your soil. You’ll flush your soil for 2 to 3 days in a row, once per day. You’ll test your last flush runoff to make sure the PH is proper. If it’s still too high or too low, you’ll allow your grow medium to completely dry for 3 to 5 days.

Once dried, you can then give another water feeding which you will test the runoff each time. You’ll continue water flushing until you’re at the proper PH range when you test your runoff. Once you’re there, allow your grow medium to fully dry out. After it’s dried you’re now in a proper range to give an adjusted feeding. This time make sure to lessen the dosage of nutrients, as you can always feed your girls more but it’s much lengthier to flush your girls of excess nutrients. It may take some time to figure out the ideal feeding schedule for soil but getting this right is crucial to your plant’s growth.

How to Fix Potassium Deficiency in Hydro?

If you are growing in hydro or a soilless grow medium you really won’t face any potassium issues that aren’t self-inflicting. So what we mean by that, is with hydroponics, aeroponics, coco, or flood and drain style setups, because you are pulling water from a reservoir, any deficiencies will be determined by your feeding regimen or dosages. Now with hydroponic nutrients, they tend to be salt, solvent, or par-synthetic blended formulas. What this does is allow direct access to the nutrients for your plants, however, you do build up excess salts, solvents, or byproducts. The benefit of that is this means microbes aren’t having to do the work to break down inaccessible nutrients to allow them to be ionized, accessed, and consumed.

So with hydroponics or soilless grow mediums you will want to be using a 25-gallon reservoir or higher for your plants. The reason being is since there is no buffer, or grow medium, to stop your plants from consuming as much as they want, as fast as they want, your PH and PPM ranges will fluctuate rapidly with smaller-sized reservoirs. As well as that, with multiple plants feeding on your reservoir, you’ll have an imbalance in macro and micronutrients inconsistently you can’t measure, which we measure using TDS Meters (measures PPM count). So larger reservoirs allow more consistent feedings or PPM, more consistent PH ranges, and more stable grows.

Fixing a deficiency in any of these setups will simply be adjusting PH ranges to the proper ones, for hydro or soilless grow mediums we recommend 5.5 to 5.9 for seedlings or vegetative phase. For flowering, we recommend 6.0 to 6.3 PH range. These ranges will allow your plants to utilize all the macro and micronutrients they’re seeking the most efficiently.

If you notice your PPM is too high, or too low, that will also determine the deficiency you’re facing. With too high PPM (parts per million) you’ll want to redo your reservoir and lower it back to an appropriate level. For hydroponics or soilless grow mediums, from seedling to the middle of vegetative growth, you’ll want 250 to 750 ppm. From the middle vegetative phase to the middle of flowering you’ll want to go from 750 ppm to 1300ppm max. Above these ranges, you will find many deficiencies, lockouts, or toxicities develop. After you’ve reached the middle of the flower stage, you’ll want to shift way down to 200ppm or less. Ideally as close to 0 as you can.

Providing the correct feeding schedule and nutrients for hydroponics is somewhat different, for reference check out our feeding chart for hydroponics.

In hydroponics or soilless grow mediums, generally the last two to three weeks, we recommend using only flushing nutrients or organic nutrients that will not stay built up like salts, solvents, or par-synthetic blends. For instance, Aphrodite’s Extraction by Nectar of the Gods can be run up until harvest as a carbon-based extraction nutrient. As well as, Terpinator or Purpinator. Both are the same product, one just has an additional amendment to help bring out the color. They are natural terpene, trichome, cannabinoid boosters, and the Purpinator has the color amendment as well. So seeking out organic flushing nutrients to help rid excess salts, solvents, or par-synthetic blend byproducts is heavily recommended. By following this PPM scale and allowing your plants to have that two to three-week flush you shouldn’t notice any deficiencies, just a natural fall fade

Happy Growing! 

We hope you enjoyed this article and be sure to have a wonderful time down your growing journey. Remember, always feed smaller dosages when testing newer amendments, if you’re a newer grower, or you’re trying a new grow medium. It’s much easier to feed more to your plant than it is to flush excess. Remember potassium is vital to the entire process of your plant consuming nutrients so be sure to stay within the proper PH ranges to maximize nutrient uptake and prevent deficiencies!
Be sure to head over to Homegrown Cannabis Co. to purchase some amazing seeds to get started on your journey towards growing. To learn even more information on growing, deficiencies, or you just want to chat head to The Homegrown Forum and sign up to our amazing forum today! It’s free! We want you amazing homegrowers to grow successfully. If you are someone who prefers to listen or you drive long hours we do have an educational PotCast. Happy Growing!