Sports Turf Manager Association

Fertilizer Grade — the percentage of nitrogen (N), phosphate (P2O5), and water soluble potash (K2O) available
Fertilizer Ratio — relationship among percentages of nitrogen (N), available phosphate (P2O5) and water soluble potash (K2O)
For example: The ratio for a 10-5-5 fertilizer is 2-1-1.
Fertilizer Analysis — nutrient content by weight
For example: In a 20-5-15 fertilizer, 20 percent of the weight is nitrogen (N), 5 percent of the weight is phosphate (P2O5), and 15 percent of the weight is potash (K2O). In a 100 pound bag, 20 pounds would be nitrogen (N), 5 pounds would be phosphate (P2O5), and 15 pounds would be potash (K2O).

Calculations
To determine the amount of elemental phosphorus (P): P2O5 x .44 = P
To determine the amount of elemental potassium (K): K2O x .83 = K

Nitrogen Sources
The source of nitrogen determines turf growth rate, density and color. Nitrogen is broken down into two categories: quick release (m) and slow release (m).

Fertilizer Programs
Cool Season Turfgrass



With active growth occuring in the spring and fall, the best time to fertilize cool season turfgrasses is from March to June and September to December. (This varies with geographic location.)
March - May: One to two applications may be necessary in the spring. This application assists with greening up the turf, but can be detrimental if there is a late frost.
June - August: Heavy fertilizer applications in the middle of summer should be avoided due to heat and drought stressing the plants. If fertilization is necessary, spoon feeding throughout the summer months will maintain turfgrass health.
September: The best time to fertilize is in the late summer. As plants begin actively growing again, fertilization promotes recovery from drought and heat related injury sustained during the summer months. Fertilization at this time also contributes to root and rhizome growth, disease and stress tolerance, and the storage of carbohydrates.
October - December: Fertilization in the late fall is advantageous because the majority of nutrients are used for root growth. There is not much vertical growth. Late fall fertilization can also be beneficial to early spring green up.

Warm Season Turfgrass



With active growth occuring throughout the summer, the best time to fertilize warm season turfgrasses is from May to September.
April - May: Early spring fertilization will assist with spring green up. One of the best times to fertilize is late spring because plants are actively growing and storing and manufacturing carbohydrates.
June - August: Fertilization can continue throughout the summer.
September: Late summer is also a good time to fertilize because plants are actively growing and storing and manufacturing carbohydrates.
October - March: If a field has not been overseeded, fertilization should not take place. 

Tips to Get the Most Out of Your Fertilizer
1. Soil test to determine the nutrients needed by the plants.
2. Depending on the turfgrass species, apply nitrogen in the amounts needed.
3. Apply nitrogen in multiple applications throughout the growing season.
4. Return clippings while mowing.
5. To avoid leaching, do not overwater.
6. Use a slow release fertilizer and apply less frequently.
7. If using a quick release nitrogen source, water it in to avoid foliar burn.