Dealing with Potassium Deficiency in Hydroponic Plants

Potassium Deficiency in Hydroponic Plants

Hydroponic plants require a nutrient for proper growth and to achieve a large yield. Some of the nutrients that most are likely familiar with include nitrogen, phosphorus, and potassium, otherwise known as the big 3 or NPK nutrients.

As we’ll discuss today, potassium plays a critical role in the growth of plants, whether cannabis or otherwise, as it’s required to help flowers and fruits form, and much more. 

Today, we’re going to determine what a potassium deficiency in hydroponics plants is, how to spot it, treat it, and prevent it from happening in the first place.

Potassium sources for plants

The most common form of potassium used in fertilizers is potassium-chloride or potassium- nitrate as seen in the General Hydroponics Flora Series:

Potassium form for Hydroponic Plants

Understanding Hydroponics Fertilizers Label – What is K20?

If we go back to the GH example, the label shows potassium as a form of K2O. 

When you see “Soluble Potash (K2O)” on a fertilizer label, liquid or powder, it tells you about the amount of potassium in the fertilizer. 

The “K2O” part is just a standard way to measure potassium in fertilizers, but it doesn’t mean the fertilizer contains something called potassium oxide.

What is K2o?

“Soluble” means that the potassium in the fertilizer can dissolve in water, which is necessary because plants can only use nutrients that are dissolved in water.

So, “Soluble Potash (K2O)” on a label means how much potassium the fertilizer can give to plants, and that this potassium is ready to be absorbed by the plants when you apply it.

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What Role Does Potassium Play in Hydroponics?       

Potassium (K) is a very important nutrient for all types of gardening, whether hydroponics or soil-based. It plays many different roles concerning the physiological processes of all sorts of plants, and this influences their overall productivity, growth, and health. So, what role does potassium play?

Root Growth and Nutrient Uptake

One of the main roles of potassium in hydroponics is to help plants develop a strong root system that is both large and efficient at absorbing water and nutrients. A strong root system is vital for the healthy growth of your plants.

Speaking of nutrients, potassium is also vital as it helps to regulate osmotic pressure in the tissues and cells of plants. Maintaining the right osmotic pressure is important to allow water and nutrients to transfer from the roots to other parts of the crop.

Photosynthesis and Flower Production

One of the most important roles of potassium in hydroponics is to allow for plants to fruit and flower properly. Potassium is linked to the rate of photosynthesis in plants, and this directly affects overall fruit or flower growth.

More potassium leads to improved stomatal control of plants, allowing them to more efficiently take in carbon dioxide and expel oxygen. It makes photosynthesis more efficient. Moreover, higher levels of potassium are associated with not only much larger yields, but also more potent ones.

Enzymatic Processes

Potassium in hydroponics is also important for a variety of enzymatic processes that plants must engage in to survive. Potassium is needed for plants to engage in protein, starch, and ATP synthesis, which in turn allow plants to perform respiration and photosynthesis. Potassium is required to turn glucose to starch, which plants require to grow.

How To Add Potassium To Your Hydroponic Water Solutions?

For home and small-scale commercial hydroponics growers, we recommend using off-the-shelf pre-mixed nutrients. Most well-known companies have created a series of suitable products that meet the plants’ needs and contain all the necessary micro and macro elements.

Following the feeding chart is a good starting point. You can make your own custom changes as you move forward and gain experience in hydroponics.

For mixing the nutrients properly, you can use the Growee smart dosing system. This system will add the nutrients according to your custom feeding chart and keep the EC/PPM within the desired range.

smart dosing system

The Causes of a Potassium Deficiency

There are a few different causes that can result in a potassium deficiency when growing hydroponic plants, so let’s take a quick look at what these are.

  • Poor Water Quality: Using water with high salts or that is “hard” can also interfere with potassium availability. Such water might contain elements that either precipitate potassium or compete with it for uptake. In this case, we will recommend using a filtration system or replacing some of the water with RO water
  • Not replenishing the nutrient solution often enough: Can lead to a potassium deficiency, For more detailed insights, check out our article on water replacement in DWC hydroponic systems.
  • pH not in range: If the pH level is under 5.5 or over 6.5, it will make the potassium less available to plants, and make it harder for plants to absorb it.
  • Environmental factors and other issues: such as disease, heat stress, excessive humidity, and excessive lighting can all cause stress in a plant to the point where it no longer properly absorbs vital nutrients such as potassium.

Competition from Calcium and Potassium

One of the most common causes of potassium deficiencies in plants is due to potassium competing with calcium. The reason for this is that plants can only intake so many of certain nutrients, with potassium, calcium, and sodium being just some of them. If there is far too much calcium or sodium present in your nutrient solution, this can prevent your plants from absorbing adequate levels of potassium (and the opposite can also be the case).

Symptoms of Potassium Deficiency in Hydroponic-Grown Plants

There are various noticeable signs of a potassium deficiency in plants, so what are they?

  • You may notice chlorosis, which is when older leaves start to turn yellow at the edges.
  • Leaves may curl up or down due to a potassium deficiency, and the leaves may become brittle as well.
  • Necrosis may also set in, which is when the leaves turn brown and die, and this happens once a potassium deficiency has progressed significantly.
  • A lack of potassium in hydroponic plants can also result in poor root growth, which results in reduced nutrient uptake.
  • In general, hydroponic plants that don’t get enough potassium display stunted growth, and worth of all, flowering will be negatively affected, both in terms of yield and potency.

How to Treat a Potassium Deficiency?

Luckily, treating a potassium deficiency in hydroponic plants isn’t too difficult.

  1. First, always use appropriate meters to test for EC levels, just to confirm that it is indeed a potassium deficiency that is the cause of the issues.
  2. Once a potassium deficiency is confirmed, use any type of water-soluble hydroponic nutrients (specifically potassium-based nutrients), and add them into your current watering solution, and make sure that everything is well-mixed).
  3. Use a Growee pH meter to test the pH level. If it is outside the ideal range, 5.5 to 6.5, use pH up or down to make the appropriate adjustments.
  4. Try cleaning your hydroponic circulation system to ensure that the nutrients and water are being properly circulated.
  5. Check for signs of a nutrient burn or calcium overload. If the lack of potassium is caused by there being too much calcium in the system, then the solution is to reduce calcium levels.
Growee smart dosing system

Preventing Potassium Deficiency

The best way to deal with potassium deficiencies in hydroponics is to prevent them from occurring in the first place, and here’s how to do just that.

  • Continuously monitor and test for potassium levels to ensure that they are appropriate.
  • Using specialized meters, measure both the pH and EC levels of the nutrient solution, and make sure to maintain an ideal range of both.
  • Regularly clean your hydroponic system to prevent sodium buildup in the pipes and tubing, and to ensure that water and nutrients circulate properly.
  • Ensure that all conditions, including lighting, heat, and humidity are all ideal, as this will minimize plant stress, and therefore allow for maximum nutrient uptake.

How Do Growee Products Prevent Potassium Deficiency?

Growee products, such as the EC and pH meter, help to prevent potassium deficiencies by allowing you to consistently monitor nutrient and pH levels to ensure that they are at the appropriate levels. Another great option to check out is the Growee Pro Combo, that not only monitors EC and pH levels, but also automatically adjusts them based on your needs. It does all of the calculating, measuring, and dispensing of nutrients for you!

Growee hydroponic system


If you notice that your hydroponic plants are suffering from a potassium deficiency, you need to take the appropriate steps to remedy the situation as soon as possible, or it may spell the end for your crop. However, with products from Growee, such as the Growee Pro Combo, you can keep potassium and all nutrient levels exactly where they should be, and all without having to do any hard work.


Signs that a plant is lacking potassium include chlorosis, necrosis, stunted growth, and a lack of flowers or fruits.

If the right steps are taken to manage a potassium deficiency, results should be visible within three to seven days.

Avoiding a potassium deficiency is easily done by regularly testing for potassium and EC levels, as well as pH, and making regular adjustments.

If a plant lacks potassium, it will not develop a strong root system, it’s growth will be stunted, and the yield will not be as high or as potent.

The easiest way to fix a potassium deficiency in hydroponics is to use supplements to increase potassium levels.

To correct a potassium deficiency in plants, using nutrients like general hydroponics or advanced nutrients is recommended for fast results.

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