By Island County Extension Agent, Donald B. Meehan
FERTILIZING HOME LAWNS
Fertilizers play a vital role in keeping turfgrasses beautiful, useful, and free from weeds as well as insect and disease damage. A good lawn needs to be well fed. Nitrogen will give your lawn a pleasing dark green color. Phosphorous and Potassium (Potash) are also necessary especially if the soil has a lot of clay. As a rule, however, our Western Washington lawns are low in Phosphorus and Potassium. As a result, fertilizers with a 3-2-1 ratio of Nitrogen (N) - Phosphorus (P) - Potassium (k) usually give best results. Some examples of fertilizer formulations are 21-7-14, 15-5-10, 12-4-8, 10-2-4, 9-3-6.
Our lawns need four to six pounds of Nitrogen per 1000 square feet each year. This can be applied as a complete fertilizer with the 3-1-2 ratio. It should be divided into four or five equal applications to provide the season's total.
Sulfur is important to enhance color and help control weeds and diseases. Select a fertilizer which contains sulfur or apply Ammonium Sulfate twice a year as part of your fertility program.
The fertilizer quantities, such as four pounds of nitrogen per year, are actual amounts of useable Nitrogen, but fertilizers you buy are never all useable plant food. They come in different forms graded by the amount available as plant food. For example a 15-5-10 grading seen on the label means there is 15% Nitrogen, 5% Phosphorous, and 10% Potassium, therefore a 100-pound sack of 15-5-10 fertilizer will only have 15 pounds of useable Nitrogen in the bag, 5 pounds of Phosphorous and on. In order to put on 1 pound of actual Nitrogen per 1000 square feet, you would need to apply 6.66 pounds of the bag's contents. That would also mean that you would have applied 1/3 of useable Phosphorous and 2/3 pound of Potassium.
If you know how many actual pounds of N, P, K, or S (Sulfur) you want to apply, take the pounds and divide them by the percentage Nitrogen figure on the bag. This will give you the number of pounds of fertilizer you need to weigh out of the bag. If you are like me, you don't have any scales to weigh things out accurately, so you can use the old rule of thumb of "A pint equals a pound the world 'round". It's not all that precise, since complete fertilizers usually weigh a bit less. If you use the mid-range of fertilizer needs, you'll be close. So, converting to the "guess-by-gosh" method we would use 7 pints, to put on 6 2/3 pounds of the complete fertilizer.
Begin applying your fertilizer in April and space the applications out over the summer into the fall approximately every two months. Adjust the timing of the applications based on lawn color. Try not to exceed eight pounds of actual Nitrogen for the year. Usually six pounds is the maximum recommended for home lawns. Using heavy applications usually turns out to be a waste of money since excess Nitrogen will leach on through before it has a chance to be used. Don't forget to water the lawn thoroughly following each application.
For more information about lawn fertilizing or other areas of concern about lawns contact our office for a copy of the publication called "Fertilizers for Play & Athletic Fields - Selection - Purchasing - Application" written by WSU Turf Specialist, Roy Goss or the "Home Lawns" publication also written by Dr. Goss.
Return to Articles Index
Return to Garden Page
Providing Educational Support to the Island County Community