potassium deficiency during flowering

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.

Deficiency and excess of Potassium in cannabis plants


There are many nutrients that influence in the development of marijuana plants; on this post, we are going to point out the most important functions of Potassium. We will tell you how to treat deficiencies and excesses of this element and the effect it has on the plant metabolism, especially in cannabis plants.

Potassium is an element found in the land in mineral form. This mineral is more or less present according to the type of terrain. Soils composed of clay are by far the richest ones in potassium, containing up to a 3%.

The potassium cycle

This element arrives at the oceans and seas through rain, aquifers, rivers, etc, where it returns by evaporation to the sky in the form of water vapour. This vapour condensates and returns to Mother Earth in form of rainfall. .

One of the ways that potassium has for its self-regeneration in the land is through animal droppings. Potassium returns to dry land to be processed again by micro-life. The remains not used by plants will be swept away by the rain and led through aquifers into the seas and oceans to return again to solid ground and close the potassium cycle.

In those regions with constant rainfalls, the substrate doesn’t properly retain this nutrient, so it isn’t found in the substrate in sufficient quantity for plants. Potassium is easily carried away by water, so we should add potassium in the form of sulphates to out nutrient solution in order to make it available for plants.

Functions of potassium in cannabis plants

Early stage of potassium deficiency

Potassium is one of the most important nutrients for marijuana plants, and although it doesn’t have much presence in the plant tissues it performs important catalyzer functions in many metabolic processes as those we list below:

  • It takes part in the photosynthesis process improving the synthesis carbohydrates.
  • It participates in the synthesis of proteins and amino acids, which come from nitrogen in the form of ammonium, so the interaction between these two nutrients is vital to perform different metabolic processes of plants.
  • It improves the resistance of plants during drought periods.
  • It increases the consistency and strength of the plant tissues.
  • Together with Phosphorus, it improves the strength and resistance of the root system.
  • The resistance against frost is also increased by acting in the sap of the plant.
  • It increases the weight, density and volume of the buds.

Intermediate stage of potassium deficiency

If there is a potassium deficiency, plants will have visible symptoms that will help us to detect it. Potassium is a mobile element so it moves from older to younger leaves when needed, since the top part of the plant has always more metabolic activity. We should make sure that our plants have enough Potassium during their life, since any lack of this nutrient will be translated into lower yields.

In the case of having potassium deficiencies, you should add more fertiliser (rich in this element) either from organic or mineral origin. Organic fertilisers are more slowly processed than mineral nutrients, which will correct this deficiency in no time and will allow you to harvest decent buds. If the deficiency is at an early stage you can simply increase the dose of your organic or mineral nutrient, what will probably solve the problem.

Advanced stage of Potassium deficiency

Potassium deficiency in cannabis plants

Visible symptoms in cannabis plants:

  • The leaves turn yellow from the tips towards the centre, ending at the base of the leaf.
  • Plants are weak and have little resistance to diseases.
  • Stems are also weak and bend easily.
  • The final yield of buds is seriously reduced.
  • An excess of calcium can lessen the capacity of the plant to absorb potassium, leading it to a deficiency of this element.

Potassium excess

Symptoms of potassium excess:

  • Blocks the absorption of other elements such as calcium, magnesium, zinc and iron.
  • Given this situation, you should flush the roots with at least triple the amount of water than the capacity of the pot; you can also add any component that helps to flush the salts away and leach the substrate. Then, you should water with a light, complete and balanced nutrient solution.

Foto 1: Potassium deficiency

The plant in the picture #1 presented a potassium deficiency that has been treated on time, without losing much bud yield and quality.

This marijuana plant was grown in an inert medium – coco-coir – and suffered a deficiency during the flowering stage, when potassium is more needed, during the 6th and 7th weeks (This plant had a flowering period of 8-9 weeks)

In the picture #2 we can see how the plant has suffered a more serious potassium deficiency.

At medium height of the plant we can see how the tips of the larger leaves are burned. Moreover, you can see with ease a discoloration of the leaves to a more yellow colour.

Photo 2: Potassium deficiency

At the top of the plant we can easily detect that the plant has been negatively affected by this deficiency. The buds couldn’t develop completely and have remained in a quite decayed condition. .

The buds of this plant won’t have superior smell or flavor since potassium is essential in terpene production.

At this stage, if you didn’t provide the necessary nutrients the yield will be seriously decreased. The buds won’t be compact and the resin production will be minimal.

These deficiencies are usually more evident and frequent in Indica strains, which are often grown without much knowledge since their flowering stage is much faster than Sativas, and the maximum demand for potassium is centralized in no more than 1-2 weeks, depending on the strain.

Since Sativa plants take much longer to flower, their nutritional needs are more progressive than in the case of Indica genetics. Still, it should be noted that Sativa strains are more susceptible to be over-fertilised than Indicas, so you should pay close attention to their needs to have a crop free of deficiencies and excesses.

In this way, choosing a balanced hybrid strain will help to control any excess or deficiency of potassium and other minerals like nitrogen or phosphorus.

In this post we show you how to detect a deficiency or excess of potassium in cannabis plants, so you can have a crop without problems and harvest the