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Potassium (K) Nutrient Deficiencies

Potassium is an essential macronutrient that is vital for optimal plant growth. Potassium deficiency can reduce resistance to bacteria and molds.

Potassium (K) Nutrient Deficiencies


Potassium is an essential macronutrient that is vital for optimal plant growth. Potassium is used in all stages of growth and promotes a resistance to bacteria and molds. It is also a mobile nutrient meaning that, when deficient, plants will move the nutrient to areas of greatest need throughout the plant.

Why Is Potassium Important?

Potassium is a nutrient that is ultimately responsible for stimulation of early growth in plants, and aids in the movement of water throughout the plant. It aides in combining sugars, starches and carbohydrates and is essential for cell division. Without sufficient and adequate amounts of potassium, growth is stunted and yields are reduced. It supports a plant’s immune system, which is an important factor even in indoor gardening. When our plants are receiving proper amounts, they are able to grow faster, promote stronger defenses against diseases, and display stronger overall plant growth.




Identifying Potassium Deficiency In Plants

Potassium deficiency results in very stunted plant growth and yellow or purple tinted leaves. Older, lower leaves look wilted with browning and curling at leaf edges and yellowing between leaf veins and around leaf edges. Left unchecked, older leaves will begin to die off and symptoms will progress to upper, younger leaves. Deficiencies leave the plant poor disease and infection resistance.


  • Older, lower leaves will often yellow.
  • Leaves curl under
  • Young leaves will wrinkle and curl
  • Necrosis will often be present at the leaf tips as well as spots on the leaf
  • All growth will be stunted
  • Stems may be soft, or in advanced deficiency, hard and brittle


Examples Of Potassium Deficiency


How To Correct Potassium Deficiency

The best defense, is to introduce simple ways to correct and prevent the deficiency in both soil and hydroponic grow systems. Because large amounts of potassium are absorbed from the root system of the plant, this is where the majority of supplementation efforts and attention should be focused.

One of the first things to take a look at is pH balance, in both soil and hydroponic growing systems. A pH imbalance will block nutrient uptake through the plant’s roots. It is important to regularly check the pH, and to be sure to keep the pH within the appropriate range for soil or hydroponics. The optimal pH range for most plants is between 5.5 and 6.5. In this range, the nutrients present in the soil or water are soluble, and are easily taken up through the plant’s root system. When the pH level is outside of this range, even when the proper nutrients are present, they are not able to reach the plant. Deficiencies are compounded by acidic conditions and excess calcium and magnesium.

If pH levels are correct then we can examine other ways the deficiency can be remedied.

One of the ways is through the use of a high quality fertilizer containing potash. When incorporated into your feeding program, a potash fertilizer will deliver a much needed potassium boost, seen almost instantly. Exercise some caution when applying potash as it's natural pH is normally above 10. Use a pH lowered mix or reduce the pH to around 6.5. Foliar feeding is not recommended in most circumstances.



Another method is concentrated kelp and seaweed treatments. Seaweed and kelp are both supplements that can provide high impact boosts of potassium and encourage healthy, productive growth. A liquid seaweed or kelp treatment can be used both at the root system and as a foliar spray in some cases.

Additionally, compost teas add abundant amounts of potassium to plants and are a great partner to seaweed and kelp supplements. The two can be mixed and used in a regimen that is capable of fixing a long list of deficiencies, including potassium.



How Do I Know Which Products Contain Enough Potassium?

The N-P-K numbers that are often displayed on the supplement will indicate the relative quantities of nitrogen, phosphorus, and potassium the product contains. If you are searching for a potassium rich product, you will want the last number, or K number, to be larger than all the others. In the image to the right, the last 0 represents the potassium number. If you aren't sure be sure to consult the product MSDS sheet to find out what it contains or contact our helpful experts for recommendations and tips.


» View all fertilizers and supplements


What If I Add Too Much Potassium?

The first step is to not panic and don't make things worse. Stop applying any amendments or fertilizers that are high in potassium. Flush plants with a mild and complete fertilizer in order to restore the balance. You should use roughly 3 gallons of flushing agent for ever gallon of soil or growing medium. In hydroponic systems, simply drain off part of the water solution and replace with clean water. Continue to test and balance the nutrient solution and pH as necessary.

Now that you know the benefits of monitoring the potassium content in your soil and hydroponic growing systems, and what to do when you spot a deficiency, you can be sure to have the necessary tools on hand to keep your plants at their best.


Want to learn more about nutrient deficiencies?

Read our entire nutrient deficiency series as well as learning about micro vs macronutrients.

Questions? Call 888-815-9763 or email [email protected].