What Does Potassium Do For Grass in the Lawn?

By Brian Mounts | Aug 15, 2020
What Does Potassium do for Grass

Understanding what potassium does for grass & lawns is good for the homeowner who wants to have healthy green grass year after year.  Potassium is an essential nutrient for all plants along with Nitrogen and Phosphorus.  Potassium ensures that your grass grows strong and is not stunted and retains a lush green and not a yellowed coloration.

Potassium is the “K” in N.P.K.  an acronym many lawn aficionados and gardeners will be familiar with when buying fertilizer.  These are the three essential nutrients that all plants including grass need to thrive.  Nitrogen, Phosphorus, and Potassium are the most common ingredients in available fertilizers and products designed to help grow your grass.

Potassium is the nutrient that is most responsible for overall general health of the plant enabling it to withstand stress, drought, and diseases.  Potassium can improve the vigor of the plant and strengthen the plant cells improving its capabilities to withstand the extremes of the elements.  Potassium is responsible for helping plants regulate processes regarding the efficient use of available nitrogen to grow well.   

Lawns that are deficient in potassium will suffer greater damage during the drought of the summer months if there is any miss in irrigation or over wear and tear from the kids or pets playing in the yard.  A grass lawn that does not have potassium readily available may end up heavily damaged during the winter and require a seeding regiment in the spring to fix dead spots and areas that became muddy due to the grass not holding up to wear.

The most commonly available sources of potassium is mined potash.  Potash is essentially a salt that contains potassium in a water-soluble form.  Potash may be referenced as muriate of potash or sulfate of potash in fertilizers.

It is naturally found in most soils;however, it is not always readily available for plants.  There are several organic fertilizers that are rich in potassium including seaweed and kelp products, wood ash, and animal feeds and bedding for animals that can be added to composts or used as mulch.

The Main Potassium Benefits for Turf Grass & Lawns

  • Plant Metabolism – Potassium helps plants to retain water and remain in balance. This allows the plant to properly regulate the amount of nitrogen and phosphorus that are absorbed at any one time.
  • Root Development – While generally phosphorus is viewed as the treatment for a plant that needs help with root development, potassium also plays a key role in establishing the roots of young plants.
  • Disease Resistance – Potassium is essential in developing the defensive mechanisms of the plant to better tolerate stresses such as temperature extremes and excess wear and tear from humans and animals.

Although those are the three main “buckets” that potassium affects in grass there are more things it does. Let’s summarize them now.

What Does Potassium do for Grass?

Facilitates Plant Development: Potassium is one of the macro-nutrients that grass needs to grow. It facilitates the growth and development of the leaves as well as the stem at the cellular level. It does this by helping the process of photosynthesis – the process by which plants make food using air, sunlight and water with the help of green Chlorophyll.

Improves Immunity & Disease Resistance: Potassium also helps to make your plant healthier by increasing its immunity to diseases and fungal attacks. If you’re looking for a healthier lawn, potassium is absolutely essential for your plant!

Improves Resistance To Stress – Adding soluble potash (K2O) to the lawn can help grass withstand things like heat stress, freezing temperatures, and drought. Basically the cellular structure of the plant is strengthened allowing it to withstand more stress that could damage it over time.

Xylem-Power Enhancer: Potassium also strengthens the overall water-carrying system of your plant. This ensures that all parts of the plant get enough water and that the plant can remain healthy. Plants without enough potassium often start to look yellowish from lack of water. You may be able to water a little less when your grass is fed adequate amounts of potassium.

Develops Roots: Potassium also takes an active role in root development and nutrient uptake. Roots are a really important part of just about any plant because they actually collect all the water and minerals from the soil. They also hold the plant firmly in the soil. Roots are important from the environmental perspective too as they help with “>erosion control.

Makes Cell Walls Stronger: Potassium also actively takes a part in making the cell walls of your grass stronger. So, if you want your grass to be a little more hardy, giving it a little extra potassium might just be the choice.

These are the main functions however here are a few more minor functions you may be interested to know about.

Aids In Nutrient Uptake: Most DIY lawn care nuts like to apply humic acid to their lawns to aid in nutrient uptake but potassium has the same effect. When your grass has low potassium available to it the root system will not uptake the other nutrients efficiently making it even harder for the grass to be it’s best. Iron, proteins, starches, sugars, and other micro-nutrients are necessary for healthy grass and potassium helps the plants pull those nutrients out of the soil.

When your soil gets too acidic, under 6.2 on the pH scale then uptake of all nutrients including potassium can start to suffer. For this reason it’s best to get your pH in line before you start fertilizing – just another reason to do a soil test before you start putting any products in your lawn.

Make sure to see the following posts for more on using humic acid in the lawn and lime, which is commonly used to fix acidity in the soil.

Obviously that’s a big list and that’s we summarize it all by saying that potassium helps the grass remain healthy throughout the year.

When to Apply Potassium on Grass & Lawns

Most lawn care companies will integrate potassium applications into traditional fertilization plans.  Applying potassium before and during the growth windows for your grass is best.  I recommend that you include potassium when fertilizing late spring, during the summer, and again in the late fall prior to the allow the grass to harden off before cold frosts appear.

Slow release fertilizers are also another excellent overall option for fertilizing your grass & lawn.  By using a mulching mower, you can slowly increase the available potassium through the leaves and grass clippings that break down and return the potassium back to the soil. This broken-down clippings and leaves is rich in potassium, but also all the other essential nutrients and in this form readily available to be absorbed by the roots of the grass and adjacent plants.

Types of Potassium Fertilizers

I use two versions of potassium products to apply to a grass lawn.  You can also view your compost and compost teas as alternative options for getting potassium to apply to your lawn, but they are not exact and will provide an unknown quantity to the grass.  Using a granular fertilizer or a liquid soluble fertilizer that you spray on the grass with the garden hose is perfect for applying to a potassium deficient lawn.  If you conduct a soil sample before applying you can be exact in your application of a granular product and like granular potash.  This is the best way to get a lawn up to specs quickly after performing a site soil assessment.

Granular Potash

Utilizing a granular potash fertilizer with a spreader is the best way to fully saturate your lawn with a potassium rich fertilizer to get your potassium numbers up to the appropriate number.  When you are first taking control of your lawn to achieve a perfect lush green yard it is essential to perform a soil assessment.  After completing a soil assessment, you will be provided with recommendations for how much fertilizer to apply to bring the numbers up to the recommended levels.

Use a drop spreader or a broadcast spreader depending on the size of your grass areas and get excellent coverage for the fertilizer on the lawn.  Make sure and time applying your fertilizer ahead of a rain event or plan on irrigating to ensure that the fertilizer is absorbed into the soil and reaches the root zone for the grass and adjacent plants.

Liquid Soluble Potash

Liquid fertilizers are an excellent option and perfect for the homeowner with a small lawn that does not justify the extra costs of purchasing a spreader.  Liquid fertilizers will connect to the garden hose and can be applied easily while watering the grass.  It is still wise to read the instructions on the box and not overdo the application of potassium as you do not want to waste the product.

Smaller grass areas benefit from a few small fertilizer applications in late spring, middle of summer, and mid fall is an excellent way to maintain a healthy lawn versus a single large application.  Liquid fertilizers have the added benefit of being applied with water making them work instantly after applying and generally there will be no issue to get the product into the root zone if you follow the instructions on the package for how to apply.

See my full grass growing guide here for more helpful tips – no opt-in needed.

Alternative Sources of Potassium

Compost is an excellent source of potassium that can be lightly applied to the yard and nearby flower beds.  A popular way to apply compost to the grass directly though is to turn it into a compost tea.  Using a large bucket, a bubbler, and a few handfuls of compost and a bunch of potassium rich materials such as banana peels and you can brew up a batch of compost tea over a week or two and then apply to the grass.  This is an organic method to care for your lawn while avoiding contributing to the over fertilization of our natural ecosystems.  Too often fertilizer products get applied heavily and end up washing away as run off.  Make a batch of compost tea and avoid the risks of over-fertilization.

Is Too Much Potassium Bad For The Lawn?

Excess potassium is not harmful for turf grasses nor is it a ground contaminant so you shouldn’t have to worry about putting too much on your lawn on accident. Of course you shouldn’t put an excessive amount down on purpose either because that would be wasteful.

A little excess potassium doesn’t really affect the plants in any way although if it’s mixed with nitrogen and you get too much on the lawn then it will burn, but not because of the potassium. Potassium is water soluble and so it gets washed away if too much is there which is why you have to apply a little bit 2-3 times throughout the year.

It is worthwhile to mention here, however, that in high concentrations, doses of potassium can have serious effects on human beings as well as animals but in typical lawn settings these extreme doses are unlikely to ever occur.

From an environmental view as well, potassium is not considered to be a pollutant. This is mostly so owing to the fact that it does not reduce the air-content in water as much as pollutants to.

Because other fertilizers can be bad in excess I like to put potassium down by itself or with specialty products to minimize the risks of putting too much of the other ingredients on the lawn.

Milorganite is a wildly popular organic slow-release fertilizer that doesn’t contain potassium at all. This is a good fertilizer for pushing foliage and root growth but for general health soil conditioner products like N-EXT’s AIR8 or Simple Plant Food’s Airate product add just enough potash to the lawn along with a few micros to build better soil and healthier turf.

In Conclusion

Potassium is an essential nutrient for all plants including grass lawns and should be included in your fertilizer plans.  Potassium provides grass the ability to grow strong and take the abuse of hot summer weather and cold freezing winters and maintain a lush green coloration.

If you are a new home owner or just starting to get serious about growing a healthy lawn, I recommend getting a soil test so you know your current level of readily available potassium, but also nitrogen, phosphorus, and other essential nutrients and minerals for plant growth.  Use the results of your soil test to apply the appropriate amount of materials to your lawn.

After making sure your grass has all the essential nutrients, you can plan to regularly fertilize your grass a few times per year during the spring, summer, and fall.  Use a balanced NPK fertilizer that provides enough potassium to prevent seeing any of the distress signs such as yellowing coloration in the grass blades.

I also recommend you take a bit more time to learn a bit more about how yards go from good to great. Here are a few other articles to get you started: