A common question that we receive is on lawn fertilization. There is quite a bit of urban legend wrapped around how much fertilizer to use, what type of fertilizer to use and when to use it. It is really a simple process that fertilizer companies like to confuse consumers over. The more you use, the more they sell, which means more profit for them. The over use of fertilizer can hurt your lawn, not to mention the environment. All you need to do the job right is a good fertilizer spreader and a little math.
For cool weather grasses, it is recommended to use a fertilizer with a 3-1-2 ratio. Some acceptable ratios would be:
3-1-2
6-2-4
15-5-10
21-7-14
Step one
Select your fertilizer type. What ratio of fertilizer should I use for my lawn? For this example, we selected a 21-7-14 fertilizer.
21-7-14
Step two
Find the square footage of your lawn/garden area. For this example we will use a 5,000 square foot area.
5,000 sq ft
Step three
How much fertilizer to use. Contact you local Master Gardeners or agricultural extension office to see what the recommend amount is. They will give you an amount of nitrogen per 1,000 square feet. For my area, the needed amount should be 3 to 4 pounds of nitrogen per year per 1,000 square feet.
Divide the needed amount of Nitrogen (4 lb Nitrogen per year, per 1,000 sq ft) by the percent of Nitrogen in the bag (21).
4lb nitrogen / 0.21 % nitrogen in bag = 19 lbs
Step four
Divide the square footage of lawn (5,000 sq ft) by the recommended application square footage (1,000)
5,000 / 1,000 = 5
Step five
Times the answer of step four (5) by the pounds of 21-7-14 per year (19 ..The answer of step 3).
5 X 19 = 95 lbs needed per year.
Step six
Divide the amount of fertilizer needed per year (95) by the amount of applications per year (2 time a year).
95 lb / 2 = 47.5 lbs per application.
So there it is in a nutshell. This formula will work for any garden/lawn area or fertilizer type.
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