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The Importance of Potassium in Fertilizer

7 min read

Losing a lawn to the stress of summer heat or the cold of winter can be very frustrating to homeowners and lawn care professionals alike. As a professional, you might spend hours tending to your customers’ lawns just for them to die off during a stressful season. As a turf-care professional, the overall goal should be lawn (and soil) health since a healthy lawn will give you the color, growth, and durability your customers are looking for. Contrary to what some people might think, the green color of the lawn in the summer or winter does not necessarily guarantee the health of the lawn. The health and success of the lawn during a stressful season is more dependent on less visible factors, like its access to and use of potassium, than many landscapers consider.

The purpose of using fertilizer is to feed the lawn with the essential macronutrients for vertical growth, root development, color, and overall plant function. Each fertilizer contains a mixture of compounds that can include the elements nitrogen (N), phosphorus (P) and potassium (K), which is denoted by the N-P-K percentages on the bag. To summarize the effects of these elements on turfgrass: nitrogen aids in the greening and upward growth of the grass, phosphorus is absorbed during germination to encourage downward root growth and establishment, while potassium is essential for the overall health and function of the plant.

Importance of Potassium

While all three macro-nutrients are important, potassium is often overlooked because its effects on the plant are not clearly visible until the plant becomes deficient in it. Potassium plays a key role in the plant’s physiological processes. During photosynthesis (the absorption of light for energy and conversion of carbon dioxide into breathable oxygen), potassium is needed in the plant to help regulate its response to light through the opening and closing of stomata (the pores that release the generated gases outside of the plant’s cells).

Potassium is also a catalyst for biochemical enzymes for the generation of Adenosine Triphosphate (ATP), which is where the plant’s energy from photosynthesis is stored. According to Thiel and Wolf, research about potassium deficiency is well documented as a significant contributor to decreased photosynthesis (1997). In addition to photosynthesis, potassium is vital for processes such as nutrient and water translocation (uptake) within the plant’s cells, cell wall turgor pressure, protein and starch production, and excretion of waste (Taurus Agricultural Marketing, 2021). Potassium plays an important role in so many of the turf’s major processes that aid in the grass’ energy creation and survivability during stressful periods. 

Signs and Symptoms of Potassium Deficiency in Grass Plants

These plant processes result in an overall healthier, high-functioning, and stress tolerant grass plant. Grass that is deficient in potassium will suffer from chlorosis (yellowing and defoliation), stunted growth, lowered adaptation to ecological variations (temperature and moisture levels), and reduced resistance to fungal diseases. It is common for potassium deficient turfgrass to not survive the stress of summer or winter. If you are unsure about the content of potassium in the soil, you should contact your local turfgrass extension for a soil test. Soil tests report the levels of some nutrients like potassium in your soil and make recommendations for applications of fertilizer to correct deficiencies.

Sources and Application of Potassium

The most common sources of potassium in fertilizers are found in the form of naturally occurring inorganic, water-soluble compounds such as potassium chloride (Muriate of Potash or MOP) and potassium sulfate (Sulfate of Potash or SOP). The term “potash” is a general term that is often used to refer to a variety of potassium fertilizers or sometimes more specifically to potassium chloride, the most widely used potassium fertilizer.

There are benefits to each of the main kinds of potash. One advantage that potassium chloride has over potassium sulfate is that its water solubility is three times the amount of potassium sulfate, making it more readily available for absorption by the plant and able to dissolve in solutions for spray applications (International Plant Nutrition Institute [IPNI], 2021). If your customers use fertigation systems, potassium chloride would be the obvious choice. However, in the same report, the IPNI states that because potassium chloride is so easily dissolved, its salinity index is three times higher than that of potassium sulfate. Higher salinization of the soil poses risks to the plant’s ability to absorb water and other nutrients, putting the plant at risk of burning up in the summer sun and heat. Another big advantage of using potassium chloride over potassium sulfate is the cost with potassium chloride costing about 40% – 50% less per pound.

Potassium sulfate’s advantage is that it does not have the same potential to over salinize the soil the way that potassium chloride can.  Additionally, potassium sulfate can help to correct sulfur deficiencies in your soil if indicated in a soil test. Both potassium variants are often used in fertilizers in combination with each other to supply the benefits of each. Potassium also can be found in natural sources such as compost, seaweed, wood ash, animal feeds and bedding materials. 


Fertilizers that contain higher amounts of potassium (whether inorganic or organic), are designed to supply the plant with enough of the nutrient to help the plant become hardier so that it may withstand periods of stress such as we see in the summer and winter seasons. Jonathan Green carries two products that contain enough potassium to help your customers’ lawns survive these stressful seasons. Turf-pro™ Stress Relief (6-0-30) and Turf-pro™ Winter Survival (10-0-20) are great fertilizer options to provide both the greening property of nitrogen and the health-boosting effects of potassium. Stop in at your local Turf-pro distributor or one of our Jonathan Green Professional Supply Centers to get one of these high potassium products to prevent the summer or winter stress from destroying all of your hard work.


Thiel, G., Wolf A.H., (1997). Operation of K+ channels in stomatal movement. Trends Plant  Sci.2:339 345.

Taurus Agricultural Marketing. (Accessed 5/17/2021). 7 Ways Potassium Promotes Healthy Crops. Taurus. Retrieved from: https://taurus.ag/7-ways-Potassium-promotes-healthy-crops/  

International Plant Nutrition Institute. (Accessed 6/14/2021). IPNI Nutrient Source Specifics – Potassium Sulfate. Retrieved from: https://www.ipni.net/publication/nss.nsf/0/ADD4AB8BDFABE40C852579AF007505D6/$FILE/NSS-05%20Potassium%20Sulfate.pdf

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