Nutrients, What Does Phosphorus and Potassium Do for my Lawn?

Phosphorus is one of the most essential nutrients for turfgrass growth and transfer of energy. Phosphorus is fairly plant mobile and also very abundant in most soils. Phosphorus leaching and runoff is a great concern and can pose a problem for local lakes, ponds and streams. This is the reason why its application is restricted and only allowed in some states when new seed or grass is layed in order to promote root development. Phosphorus does bond well in soil and as a result is seldom found to be deficient, leading to soil fertility reports eliminating the need for future applications unless under previously stated reasons.

I always remember phosphorus’ purpose as simply “Root Tips and Shoot Tips”. I remember Potassium’s purpose as “Health, Strength, Flower and Fruit”.

Potassium is an underrated element for the home lawn with most hardware stores concentrating on Nitrogen fertilizers rather than Potassium due to the lack of visual result from potassium. Potassium though is essential in keeping a strong resilient grass that becomes more tolerant to cold and heat after an application. Low potassium plant levels have low vigor as a result of low osmotic pressure in the plant leading to the plant providing limited pressure to uptake water and nutrients. Potassium thickens the grass cell walls which increases its wear tolerance.

So, to put it into Lehman’s terms, Phosphorus use should only be for newly seeded areas or new sod in order to promote root development. Potassium should be used to keep the plant strong against all external factors. Potassium applications before heat can aid in the plants heat tolerance. For me on the golf course, I apply Potassium before big tournaments because it makes the grass firmer (more water in plant cell) and helps it tolerate all the play its going to get (thicker cell wall). In terms of your yard and application would be good mixed with a Nitrogen app before summer in order to help cope with summer and kids’ activities. A typical ratio of Nitrogen to Potassium fertilizer is a 3:2 meaning 3 parts Nitrogen and 2 parts Potassium. So, if you’re looking at a fertilizer that is a 19-0-6 it may not be the best purchase for your lawn and a 19-0-12 would be more suited. Capitalism runs the country so formulations like this are harder to find. Maybe better looking for fertilizer at your local landscape supply store rather than the hardware store.