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Often seen on fertilizer labels are a series of three numbers representing N-P-K. For those that never took chemistry or tried to put that class behind them many years ago, N-P-K is the shorthand chemistry notation for Nitrogen-Phosphorus-Potassium. These are the main nutrients in soil fertilizers. Because different soils have differing amounts and the nutrient requirements change depend on the plant species and stage of development , the amounts of these three nutrients will vary. They will vary with seasons, with weather, with geographic areas, with previous plantings and many other conditions. Fertilizer is one of many amendments added to soil for the purpose of enhancing healthy plant production. Both organic and inorganic fertilizers are available. Both organic and inorganic products can be manufactured and sold at your local garden center. The easiest way to note the difference between the two is that organic originates from animal/plant based material that undergoes a natural process to provide an end product; while inorganic fertilizers are synthetic products made from chemicals using inorganic substances. Both products provide beneficial outcomes. The organic vs inorganic option is clearly one of choice. Each gardener is encouraged to research the differences and choose the product that will meet their individual needs. For some, the choice may be affected more by use than preference.

With it being late August, it may be a bit too late for some or a bit too early for others to discuss fertilizer in much detail. Most gardeners have been fertilizing their gardens about every 4-6 weeks throughout the growing season. Applying fertilizer in the spring is to boost new plant growth. Now we are in late summer/early fall with the attention for fertilizer shifting to lawn maintenance. Although, if you are a cool-crop gardener, you may consider adding amendments when planting new plants for fall harvest.

A basic understanding of what benefit each nutrient provides will ease some of the confusion associated with those products over-shelved with vibrantly colored labels that read 10-10-10 or some other 3-series number or for this plant, some other plant. Then throw into the mix organic, inorganic, mixed, concentrated, one-time use, shade lawns, sunny lawns, on a never-ending list of eye-catching advertising which seems to goe on and on until you are standing bug-eyed and ready to give up! Ugh!

The “three numbers” on the product label represent the ratio percentage in weight among the three most important nutrients for successful plant growth.

The first number will be Nitrogen (N) and considered the most important nutrient for plant growth above the soil level – grass, stems, leaves. Simply stated, it puts the “green” in plant. Too much N will result in rapid growth with a weak root system and possibly cause burning to the leaves. Having too little N will lead to the plant losing its green color.

The second number will be Phosphorus (P). Phosphorus stores and transports the energy required for plant growth, root development, and disease prevention. Too much or too little phosphorus impacts the plant root system.

The third number will be Potassium (K), often reffered to as potash. The role of K is to absorb water and nutrients for the plant. This amendment strengthens the plant to endure environmental stresses such as weather extremes and diseases. Too much or too little K is less harmful to your plant/lawn than other nutrients, but can affect the N level causing a balance shift in the soil.

Cool-season grasses are mostly grown in our area and benefit the most from adding amendments in late summer and early fall. Purdue recommends as a rule, applying 1lb of N per 1,000 square ft of ground from Aug to Nov. One hint to maximize the effectiveness with amendment applications is to coordinate with natural moisture. Avoid long dry hot spells in the weather and take advantage of early morning dew and rainfall forecasts. This practice will be one step in preparing your lawn for winter.

Being introduced to N-P-K is just the beginning. There is much to learn and many factors to consider as you navigate the world of amendments for what will make your perfect landscape. One resource for lawn fertilizing – https://turf.purdue.edu/.

Send us your questions and comments to the Shelby Purdue Extension Office – 317 392 6460 ext. 0 and https:// extension.

Purdue.edu/Shelby