Fertilizer recommendations are based on the amount of actual nitrogen a lawn needs in a year. The amount of grass fertilizer you decide to apply should take into account several factors, including the type of grass you have planted and the size of your lawn.
Different types of grasses need different amounts of nitrogen to keep them vigorous and healthy. The following table lists the yearly nitrogen requirements for 1,000 square feet of the most common lawn grasses.
That recommended nitrogen range shown in the table has to do with the length of the growing season. If you live in a cold-winter climate where the seasons are short, you use the lower end of the range. If, on the other hand, you live in an area where the summers are long and the winters are mild, you use the upper range. Basically, the longer the growing season, the more nitrogen the grass needs.
| Grass Type | Pounds of Nitrogen per 1,000 Square Feet |
|---|---|
| Bahia grass | 2 to 4 |
| Bentgrass | 4 to 6 |
| Bermuda grass, Common | 2 to 6 |
| Bermuda grass, Hybrid | 4 to 6 |
| Blue grama | 1 to 2 |
| Buffalo grass | 0 to 2 |
| Centipede grass | 1 to 2 |
| Fine fescue | 2 to 3 |
| Kentucky bluegrass | 4 to 6 |
| Ryegrass | 2 to 4 |
| St. Augustine grass | 4 to 5 |
| Tall fescue | 2 to 6 |
| Zoysia grass | 3 to 4 |
Now you can see how important actual nitrogen is. Notice that the numbers in the previous are based on a lawn’s requirement for an entire year. You need to break the total amount into several applications, applying about 1/2 to 1 pound of actual nitrogen each time. Apply any more than that, and you may burn the lawn. Any less, and you don’t get much effect. You can add some slow-release fertilizers in larger amounts.
The amount of a fertilizer you have to apply to achieve that 1 pound of actual nitrogen per 1,000 square feet, naturally, varies by the percentage of nitrogen in the product.
| Percentage of Nitrogen in the Fertilizer Bag | Pounds of Fertilizer to Apply to 1,000 Square Feet |
|---|---|
| 1 | 100.0 |
| 2 | 50.0 |
| 3 | 33.3 |
| 4 | 25.0 |
| 5 | 20.0 |
| 6 | 16.7 |
| 7 | 14.3 |
| 8 | 12.5 |
| 9 | 11.1 |
| 10 | 10.0 |
| 11 | 9.1 |
| 12 | 8.3 |
| 13 | 7.7 |
| 14 | 7.1 |
| 15 | 6.7 |
| 16 | 6.3 |
| 17 | 5.9 |
| 18 | 5.6 |
| 19 | 5.3 |
| 20 | 5.0 |
| 21 | 4.8 |
| 22 | 4.5 |
| 23 | 4.3 |
| 24 | 4.2 |
| 25 | 4.0 |
| 26 | 3.8 |
| 27 | 3.7 |
| 28 | 3.6 |
| 29 | 3.4 |
| 30 | 3.3 |
| 31 | 3.2 |
| 32 | 3.1 |
| 33 | 3.0 |
| 34 | 2.9 |
| 35 | 2.9 |
| 36 | 2.8 |
| 37 | 2.7 |
| 38 | 2.6 |
| 39 | 2.6 |
| 40 | 2.5 |
| 41 | 2.4 |
| 42 | 2.4 |
| 43 | 2.4 |
| 44 | 2.3 |
| 45 | 2.2 |
| 46 | 2.2 |
If you wonder why this stops at 46, that’s the percentage of nitrogen in urea, the most potent fertilizer you can buy. These figures have been concentrating on dry fertilizers because that’s the form most often used on lawns. Liquid or water-soluble fertilizers, which you usually apply through hose-end sprayers, are also available for lawns. Liquid fertilizers are more difficult to apply evenly, and you need to repeatedly refill the hose-end sprayer. The best advice for using liquid fertilizers is to follow the directions on the label.
All recommendations are based on 1,000 square feet of lawn. To find out the total amount of fertilizer you need for one application, divide the square footage by 1,000 and multiply that by the appropriate number in Column 2 2.
Nitrogen leaches through sandy soils very quickly. If you have sandy soil, you can increase fertilizer efficiency by applying less with each application but applying it more often. Or, use only slow-release fertilizers.
If you mow often enough, leaving the clippings on the lawn adds nitrogen to the soil; you can cut the amount of fertilizer you apply by 25 percent, maybe more. And, no, lawn clippings don’t cause thatch.