Potassium Deficiency In Cannabis Plants – A How-To Guide
With potentially deadly consequences and a higher chance of appearing in the flowering stage, a potassium deficiency can be dangerous. Make sure you’re prepared to prevent and even solve it if a deficiency arises.
HOW TO IDENTIFY?
Just like you and I, all living things require a very specific set of conditions to survive. But survival is not the only factor to take into account when growing cannabis. In order for plants to yield the best buds they can, you’ll have to take extreme care to ensure a thriving crop. This includes noticing deficiencies in time to correct them. Today, we’ll be covering just one – potassium deficiency –, although the procedures are similar amongst many different deficiencies.
THE FUNCTIONS OF POTASSIUM IN CANNABIS
In cannabis, potassium is essential for many important functions. It takes part in the photosynthesis process, which gives the plant its green colour, and is crucial to plant health and development. During a drought period, potassium is the nutrient that improves a plant’s resistance, not that you should go any period without watering your plant. This is more important for cannabis that grows freely in nature as it’s responsible for aiding the movement of water through the plant.
In conjunction with phosphorus, potassium increases the strength and resistance of the root system as well as the plant’s tissue. This will also help protect the plant from harsh, cold weather.
Considering all these factors, it’s clear to see how potassium is essential for your marijuana plants. However, your average grower will give more importance to how this nutrient affects the buds of the plant. Potassium is a nutrient that helps increase the weight, density, and volume of your delicious nugs. This is why being able to recognise and fix this deficiency is an important skill to have as a grower.
VISIBLE EVIDENCE OF DEFICIENCY
It’s important to note that if you are currently handling plants in a hydroponic system, you won’t have to worry about this. Potassium deficiencies are extremely rare in water-based systems. If you have similar visual symptoms, make sure you double check your system before treating it for this problem.
Deficiencies do happen in soil and other mediums every so often. The most common symptom you’ll notice is a brown or yellow colouring in the tips and edges of the leaves. With the passing of time, these will curl up, appearing burnt – much like an iron deficiency. Another thing that will raise suspicion is stretching. If one plant seems to be taller than the others around it, it’s not a good sign as this weakens the stems.
The appearance of spots on the leaves will be the symptom to follow. Firstly, you’ll see those necrotic spots characterised by their brown tonality. Left untreated, more spots will begin to show. This time with chlorotic ones, characterised by a white colour. The veins of the leaves will keep their green colour, unlike many deficiencies. What you’ll notice shifting colour are the petioles and stems, now showing red tones.
Although previously, you might’ve noticed the plant stretch out, it was not growing. This deficiency slows down plant growth. Leaves will grow small in size, and this is when the deficiency becomes most dangerous. Potassium shortages are very mobile. They move around the plant very fast, unlike most deficiencies. This one will spread to the larger fan leaves where it will most likely kill them.
WHAT CAUSES IT?
Before implementing any changes to your grow medium or watering solution, take a look at your lights. With strong LED and HPS grow lights, you might be overheating the leaves. These will show burn symptoms even if the overall temperature is cool. Just make sure you check for this first. Move your plants further away from the lights for a couple of days to determine the root of the issue.
In case lights are not the problem, the deficiency might be caused by an excess of fertilizers and nutrients. Excess salt is especially common as it tends to build up in the growing medium.
Nutrient lockout is a very common cause of most deficiencies. When the pH of the soil is too low, it makes the medium too acidic. This causes stress in the root zone and prevents the uptake of potassium. How can you stop this?
HOW TO FIX THE PROBLEM
When it comes to the pH issue, make sure you establish and maintain a healthy pH throughout the entire life cycle. In soil grows, the pH value should be fairly neutral, between 6.0-7.0 for the optimal potassium uptake. As for hydro systems or coco coir, a slightly more acidic pH would be recommended. Between 5.5-6.5 is ideal for this. To fix pH issues, make sure you flush your medium. Use neutral pH water to remove the excess nutrients in the soil. Only include half of your usual nutrient solution in the water.
You might also be overwatering your plant. Proper watering practices will go a long way in keeping a plant healthy. The method and frequency with which you water will impact your future buds massively. Don’t overlook this.
Make sure you read the labels of your supplements to see how these nutrients interact with each other. Too much of some will lock out others. Calcium and nitrogen will decrease the absorption of potassium, for example. Just be sure not to use too much of something without a full understanding of what it does.
You can always use a supplement rich in nitrogen, phosphorus, and potassium. Only do this after you’ve flushed the plant. Give the plant time to recover and be on the lookout for the newer leaves and how they grow.
When plants suffer from a nutrient deficiency, they are weak and have little resistance to disease. This is why it’s important to know how to detect and fix the deficiency in time. Potassium is essential for terpene production. If not enough is supplied, your buds will lack flavour and smell. The flowering stage is where you’ll most likely face a deficiency like this.
CARE FOR YOUR PLANTS
Hopefully, you’ve learned more about potassium deficiency and all deficiencies in general. Next time, you’ll be able to fix this problem comfortably and in a timely manner. Only through experience will you be able to obtain the best yields you can. Deficiencies are reversible and easy to solve if you know what you’re doing, and now you do. Best of luck with preventing and solving potassium deficiency!
Nutrient deficiencies are a very common problem amongst growers. This one, however, might have dangerous consequences if not taken care of in a timely manner.
What Does a Cannabis Potassium Deficiency Look Like?
Leaf Problem / Symptoms: With a marijuana potassium deficiency, you’ll generally see symptoms on older leaves, but not always. Sometimes you’ll see the symptoms at the top of the plant. Leaves with a potassium deficiency get yellow, brown, or burnt edges and tips. The burnt edges may look a little like nutrient burn, except the affected leaves also start turning yellow in the margins.
Example of a marijuana potassium deficiency with common leaf symptoms
You may see the brown burnt edges first, or you may see the yellowing first. When the leaf symptoms are both present, it’s a good sign you have a potassium deficiency in your leaves.
Plants may stretch and stems may become weak, but leaf symptoms are more noticeable. The leaf symptoms appear somewhat similar to an iron deficiency in that they can turn bright yellow, but the tips of the leaves curl as the edges turn brown, burn and die.
Cannabis potassium deficiencies can cause your cannabis leaves to turn white, yellow, brown or burnt looking, but the inside veins almost always stay green. Sometimes a Potassium deficiency is made worse by overwatering, as was the case with this plant.
Sometimes you’ll get something that looks a lot like tip burn with a potassium deficiency, but it goes in further than nutrient burn, and with a potassium deficiency you also see yellowing between the leaf margins
Sometimes the burn can appear pale, bleached or yellow, instead of brown. If you look in the background of this pic, you can see some of the leaves have turned brown in addition to the bright yellow leaf in the front. These are all signs of a marijuana potassium deficiency.
Potassium deficiencies are commonly mistaken for other nutrient problems!
Sometimes the first symptoms of a cannabis potassium deficiency look a lot like nutrient burn. One difference is the edges of the leaves will also start turning brown, where nutrient burn usually only affects the tips. And unlike with nutrient burn the leaves of a potassium deficiency turn yellow in the margins, especially near the burn edges.
This is not nutrient burn, it’s actually the first stage of potassium deficiency!
Could it actually be light burn?
Keeping your grow lights too close, for example with powerful LEDs and HPS grow lights can give your plants “sunburn” even if the temperature is cool! This can sometimes look like exactly like a cannabis potassium deficiency when the true problem is your grow lights are too close to your leaves.
These leaves look like they have a potassium deficiency but the symptoms are actually caused by light burn (grow lights being kept too close)
Solution for Potassium Deficiency in Cannabis
Note: Sometimes a cannabis potassium deficiency (like all deficiencies) can be triggered by stressful conditions (for example overwatering, heat, transplant, etc) and may clear up on its own after the period of stress is over. If you only see one or two affected leaves near the bottom of the plant, and the problem isn’t spreading, I wouldn’t worry too much about it!
1.) Make Sure It’s Not Light Burn
When a cannabis plant is kept too close to the grow lights, it can get light burn which looks almost exactly like a potassium deficiency. If you’re using powerful lights like an LED or MH/HPS, consider moving the light away a few inches further away to see if that stops the problem from spreading. LEDs or MH/HPS should never be kept closer than 12″ away, and most models should be kept further. How far away do I keep my grow lights?
2.) Use Good Sources of Nutrients
Most cannabis growers don’t need to add more nutrients if their leaves are experiencing a nutrient deficiency. In fact, most growers have actually already given plenty of potassium to their cannabis plants, whether they meant to or not. If you’re using quality soil or cannabis-friendly nutrients, you probably don’t need to worry about adding more patassium.
Potassium deficiencies are generally more likely to appear when a grower is using heavily filtered or reverse osmisis (RO) water to feed plants, but as long as you’re giving your plants a good source of nutrients, you probably need to…
3.) Adjust pH to Correct Range
But the reason most growers see potassium deficiencies is because potassium is best absorbed at lower pH ranges. When the pH gets too high, your plant may exhibit signs of a potassium deficiency even if it’s physically there near the roots.
In soil, potassium is best absorbed by the roots in the 6.0 – 7.0 pH range
In hydro or coco coir, potassium is best absorbed by the roots in the 5.5 – 6.5 pH range
4.) Watch Leaves for Recovery
If you suspect your growing cannabis plant has a potassium deficiency, flush your system with clean, pH’d water that contains a regular dose of cannabis-friendly nutrients. Old damaged growth will likely not recover. Watch plant over next few days to make sure that the problem stops spreading to new growth.
If you cannot get rid of your potassium deficiency and want to look at more pictures of cannabis leaf symptoms…
- Bronze or brown patches
- Brown or slimy roots
- Brown or yellow leaf tips/edges
- Buds dying
- Buds look odd
- Bugs are visible
- Curling or clawing leaves
- Dark leaves
- Drooping plant
- Holes in leaves
- Mold or powder
- Pink or purple on leaves
- Red stems
- Shiny or smooth leaves
- Spots or markings
- Twisted growth
- Wilting leaves
- Yellow between leaf veins
- Yellow leaves
This page is part of our Plant Doctor series. You can use our tool to filter by symptom and help diagnose your plant.
Leaves with a potassium deficiency have yellow, brown, or burnt edges and tips. It may look like nutrient burn, but the leaf margins also turn yellow.