FAQ: Fertilizer & Turf
What do the numbers mean on the fertilizer package?
The ideal fertilizer is designed to meet the nutritional requirements of the plant it serves. Mineral nutrients are classified as major, secondary and minor elements. The three major mineral elements of a typical fertilizer are Nitrogen, Phosphorus and Potassium—often referred to by their chemical symbols "N", "P" and "K.” So, a fertilizer with a guaranteed analysis of 25-3-5 would consist of 25% Nitrogen (N), 3% Phosphorus (P205), and 5% Potassium (K2O). No one essential nutrient is of greater importance than any other. All of the essential elements are necessary for proper development of turfgrass, but the major and secondary elements are needed in larger quantities than the minor elements.
Why are the N-P-K numbers more important than the secondary?
Nitrogen is an essential part of all living matter. It is the basis for amino acids that combine to form proteins. Nitrogen is associated with above-ground vegetative growth and density of turf, as well as its deep green color. Deficiency is noticed in turf that has turned light green or yellow. The blades start dying at the tip and progress along the midrib until the entire leaf is dead.
Phosphorusis the key nutrient in seedling development since it contributes so much to initial root development and seed formation. It is directly related to the vital growth process. Deficiency is most likely to be observed in seedling growth when new seedlings are slow to develop. On established grasses the leaves tend to turn purple.
Potassium(also known as potash) is found in large quantities in the plant. Potassium is associated with winter hardiness and disease resistance in turf. Deficiency will appear in the blades becoming streaked with yellow, turn brown at the tips and eventually die. Susceptibility to disease and winter injury is also increased.
There’s a lot of talk about adjusting soil pH before doing anything else. How do I measure and adjust accurately?
A soil may be alkaline, acidic or essentially neutral. The alkalinity or acidity of a soil is measured by its pH. All pH values occur somewhere in a scale running from 0 to 14. A pH of 7 is neutral with numbers less that 7 indicating acidity and numbers over 7 being alkaline. It is commonly accepted that a pH range of 6.5 to 7 is good for raising turfgrass. In the ideal pH range the overall availability of the major elements is “unlocked’ to the plant’s advantage. When the pH strays too far from this ideal, nutrients become less available and more difficult for the plant to use.
It is possible to improve soil pH by adding high-calcium lime to acidic soils. In the other extreme, sulfur in various forms, can be used to acidify excessively alkaline soils to a more ideal range. To learn how to take a soil sample and where to send it for analysis, download this Soil Info PDFnow. It’s wise to have a soil test to determine if the pH needs to be raised, lowered or left as is—as well as to reveal the fertilizer deficiencies (or over applications!) in your soil.
Sulfur is an essential part of certain amino acids and proteins. Together with nitrogen, this element makes new protoplasm for plant cell growth. Deficiency is similar to that of nitrogen in that the leaves will turn light green or yellow, then turn brown, and eventually die.
What about amending the soil’s minor elements?
Iron plays an integral part in chlorophyll production and is also a part of many enzymes. It is responsible for giving turf its deep green color. Deficiency symptoms include chlorotic or even white young leaves due to a reduction or loss of chlorophyll.
Other Minors are essential but not discussed here since most soils have the minor elements in necessary amounts. A complete soil test will determine if any of these minor elements are needed.
Lawn Starter. Apply 10-10-10, 13-16-20 or a similar balanced fertilizer at a rate of 25# per 2500 sq. ft.
Lawn & Turf Maintenance. General rule of thumb is to provide 1# of actual nitrogen per application per 1000 sq. ft. repeated three to four times per year (about every 6-8 weeks throughout the growing season for a healthy lawn. Apply 25-3-10, 20-5-10 (or similar blend) at a rate of 20-25# per 5000 sq. ft. of lawn area. Additions of iron and sulfur are also desirable.
Lawn Winterization. Apply 10-10-10, 13-16-20 or a similar balanced fertilizer at a rate of 25# per 5000 sq. ft.
Herbicidescan be included with fertilizer applications. Follow directions and applications on the bag that generally corresponds with above rates.
Garden, Flower Beds and Planters. 2 to 3 applications per growing season of 10-10-10 (20# per 800 sq. ft.) OR 19-19-19 (10# per 800 sq. ft.).
Trees and Shrubs. Scatter 3-4 applications per growing season around the base of tree or shrub out to the drip line.
- Small (<3’ shrub or <10’ tree): One small handful of 10-10-10
- Medium (3’ shrub, 10’ tree): One large handful of 10-10-10
- Large (>3’ shrub or > 10’ tree): 2-3 handfuls of 10-10-10