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Should I Fertilize in the Fall? How Much?

With the arrival of fall comes the opportune window of time to take care of your yard and prep the lawn properly to survive the frost of winter. We recently covered our top lawn care tips for the fall, with the first and most important bit of advice being to fertilize your lawn.

The general rule of thumb is that fall is the ideal time to fertilize your lawn. Homeowners in the Northeast especially should fertilize their lawn with up to two layers over the course of the season in order to create hardy, lasting grass come spring. Fall is the preferred season for fertilizing because the morning dew creates the perfect conditions for your grass to absorb the nutrients in the fertilizer.

However, no two lawns are the same. Deciding if you should fertilize your lawn and how much fertilizer to use depends on what type of grass you have in your yard and the climate where you live. Keep reading to find out exactly when and how you should fertilize.

What Grasses Should Be Fertilized in the Fall?

If you live in the northern regions of the country the fall is definitely when you want to fertilize. The following cool-season grasses should be fertilized in the fall:

  • Fescue
  • Bluegrass
  • Ryegrass

Fertilize these grasses once in early September and again in November, before the first frost. If you have warm-season grasses in the South you should avoid fertilizing unless your grass has been overseeded with winter ryegrass.

How Much Fertilizer Should I Use?

Grass fertilizers are mostly nitrogen accompanied by smaller percentages of potassium and phosphorous. When you buy fertilizer you will see the percentages of each of these elements listed on the bag with dashes separating them. For example, 30-5-10 indicates a fertilizer with 30% nitrogen.

The amount of fertilizer you will need to use is proportional to how much nitrogen is in the fertilizer. Using too much fertilizer is just as harmful as using too little, so it’s important to get an accurate measurement of how much to use.

We recommend this convenient fertilizer calculator to get a pretty close measurement. For example, for a lawn of 5,000 square feet using a fertilizer with 30% nitrogen you’ll need 11.7, or 12, bags of fertilizer. If the percentage of nitrogen drops to 20%, however, you’ll need 17.5, or 18, bags of fertilizer.

Remember to check the forecast a day before you plan to fertilize your lawn. A heavy rain right after you’ve spread fertilizer will create hazardous runoff full of chemicals that should not enter your local water supply. Read up on the local laws to determine if the amount of fertilizer you’re using is compatible with ordinances relating to environmental runoff and contamination.

If you live in an area near multiple farms and agricultural sites you can’t be confident that your drinking water is clear of nitrates even if you follow proper protocol for fertilizer on your own property — all it takes is one mistake from someone nearby to jeopardize your water quality. Luckily you can order a Nitrate Reduction Water Filter to safely reduce the amount of nitrogen in your water from fertilizers and septic systems.