cannabis potassium toxicity

Excess or lack of potassium in marijuana

Chemical symbol for potassium with two cannabis leaves

The symptoms of a deficiency or lack of Potassium in marijuana plants are easy to recognize, as long as you’ve read this article before of course… So, I’ll explain you how to identify this nutritional problem.

? Lack of Potassium Symptoms

  1. Older leaves start yellowing from the tips inwards
  2. The stems and petioles of the leaves weaken and cease to be erected.
  3. Plants become more vulnerable to pests and diseases
  4. Development rate slows down, affecting final production

Image of a cannabis plant affected by a severe potassium deficiency*

Now we are going to take a closer look at each of these points, to facilitate the task of identifying a Potassium deficiency in cannabis.

1 Why do you see it earlier in the older leaves? This is because Potassium is a macro-element, and these are mobile within the plant, so when it lacks to form new shoots, it takes the stock from the lowest leaves.

2 The stems and petioles of the leaves lose strength for several reasons, the main one being malnutrition itself, but they are also weakened by the inability of the leaves to carry out photosynthesis properly.

3 Many times the lack of nutrients in weed is associated with other misfortunes, such as pests and fungi attacks. This is because when the plant is healthy it has a much stronger immune system, just as it happens to us humans.

4 When cannabis plants are healthy, it is almost as if their growth can be seen with the naked eye, it is the plant that develops fastest. But that speed slows down drastically when they lack some macronutrient, something that is easily perceived.

✅ What causes lack of Potassium?

  1. Poor substrate quality
  2. Inadequate PH
  3. Excess Calcium blockage in irrigation water or substrate
  4. Lack of Potassium in the nutrient solution
  5. Blockage by excess of salts in general

As a general rule, when we suffer a deficit of Potassium in cannabis crops is for one of those 5 reasons but, why does this happen?

1 We all have met a grower friend who, by trying to save some money on substrate, ends up buying a low quality one. This is a big mistake, you save a small amount and it will usually cause you problems, so we strongly recommend growing with quality soil.

If we cultivate with a quality substrate and detect that the plant lacks Potassium, it can only be for one of the other 4 points. What we usually do is discard until we find the problem, more or less like doctors do.

2 The pH of irrigation water is very important for the absorption of nutrients. Potassium has an optimal pH range between 6.1 and 7.1 approximately, so values above or below that range can cause a lack of K.

3 An excess of Calcium can cause a lack of both Potassium and Magnesium. The balance between the elements that nourish the cannabis plants is indispensable, because some are antagonists of others, and when there are excesses of ones they can provoke the blockage of others.

4 All the cannabis varieties do not eat the same, in nature the Landraces have been adapting to their environment over the years. But today most commercial genetics are hybrids and polyhybrids, with different nutritional needs. Sometimes it happens to us that because we are afraid to use too many composters, we give them less fertilizers than plants need at that moment, causing a deficit of Potassium among other disorders.

5 This usually happens in crops where the plants have been in the same pot for a long time. It is due to the accumulation of salts in the root system, since roots do not assimilate the whole fertilizer, and the excess remains in the substrate, which gradually interfere with the perfect absorption of nutrients. The use of Enzymas and root washing corrects this problem.

Image where you can see the evolution of a lack of Potassium in cannabis leaves

? Too much potassium in the marijuana plant

Besides the lack of potassium, it can also be in a situation of excess thereof, therefore, blocks the absorption of other minerals, such as calcium, magnesium, manganese, zinc or iron..

This excess, visually, causes the plant has a much darker color. If in the case of lack plant was becoming yellowish, in this case it turns dark brown. In addition, it will give way to other multiple deficiencies caused precisely by this overfertilization.

If this is your case, but still time to save your plant because this is not dead or has not been greatly affected, you must take charge and give you a solution. Is there any perfect? The word would not be perfect, but simply a quick and effective response to the problem that your plant right now.

Thus, in these cases, the solutions to follow are the following: firstly, a wash of roots, so that they can return to absorb all the nutrients. They are getting your plant develops as expected it. Some may even improve many of the processes that follow the plant until we collect the fruits expected during harvest. Returning to the subject of washing, it is recommended to do so with at least triple water capacity of the container.

During this root cleaning, we can also add an enzyme solution to the water with which we water our plant, helping to break down the salts and thus leach the substrate. Once this step has been carried out, it is recommended to water with a light and complete fertilizer.

Do you recognize with the naked eye a lack of potassium in cannabis crops? ⚠️ In this article we easily show it to you ✨ It will never affect you again.

Potassium Deficiency

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…

Plant 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
  • Webbing
  • 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.