Lawn grasses such a zoysia, Kentucky bluegrass and Bermuda grass are only native to a fraction of North America. As a result, they are often placed in soils that do not have sufficient nutrients to maximize their growth. This, coupled with the fact they are competing with local weeds, means it's a good idea to use a specially formulated grass fertilizer once or twice a year to give your lawn a leg up. Grass fertilizers come in a 6-8-5 N-P-K mixture, but that's not helpful unless you know what N-P-K means.
The N in N-P-K stands for nitrogen. It makes up 6 percent of the total formula in 6-8-5 fertilizer. Nitrogen is needed by all plants to create chlorophyll, which makes grass green. Grass can derive nitrogen from different chemicals, depending on the brand of fertilizer and how it's introduced to the grass. Anhydrous ammonia and aqua ammonia are liquids that must be injected into the soil from pressurized tanks to be effective because they will turn to a gaseous state when exposed to the open air. Sodium nitrate, potassium nitrate, calcium nitrate, ammonium nitrate, ammonium sulfate and urea are all solid sources of nitrogen that release into the soil slowly every time the grass is watered.
The P in N-P-K stands for phosphorous. It makes up 8 percent of the total solution in grass fertilizers. Phosphorous is a crucial building block for grass's complex and sprawling root system. Polyphosphate and superphosphate are easily soluble crystalline chemicals that are typically delivered in a liquid solution. Rock phosphate is literally powdered phosphorous, and though it's highly effective, it is expensive to ship from mining site to processing facilities to stores because of its high molecular density. Diammonium phosphate and monoammonium phosphate are included in dry and time-released mixes that will seep into the soil over a period of months.
The K in N-P-K stands for potassium. It is necessary to promote the overall health of grass's vascular structure and increase grass's resistance to infection and disease. Flowering and fruit-bearing plants utilize more potassium than nonflowering plants. It only makes up 5 percent of the total solution because grass obtains most of its required potassium from the soil. All ingredients containing potassium are derived from potash, or plant ashes, making them useful in both dry mixtures or liquid solutions. These ingredients are potassium sulfate, potassium chloride, potassium magnesium sulfate, potassium hydroxide and potassium nitrate.
A 6-8-5 fertilizer obviously doesn't add up to 100 percent. This is because a fertilizer that did would be too strong and burn the grass, killing it. A small amount of supplemental ingredients that grass uses in minute quantities are included. These ingredients are magnesium, calcium, sulfur, iron, manganese, zinc, boron and molybdenum. The rest of the fertilizer mixture is made up of inert ingredients like soil, vermiculite and peat moss.