When and How to Fertilize Your Lawn in the Fall

It’s easy to think that because the calendar has turned over to Fall, that you’re done with lawn care for the year. Surely you don’t need to fertilize this time of year, right? Wrong. Your final fertilizer application of the year is the most important one. Let’s explain.

Why Fertilize the Lawn in Fall?

Like the rest of us, your lawn gets tired by the time summer ends.

Your lawn has struggled through a long, hot relentless summer. It’s endured excessive heat, humidity and drought. It’s been trampled by kids, dogs and overuse. Weeds, insects and diseases have taken their toll. Your lawn is hungry and tired. It wants a good meal before it settles in for a long, well-deserved winter slumber. Here are a few tips for keeping your lawn green in the summer heat.

So why fertilize your lawn in the fall?

• This is your lawn’s last chance to thicken up, restoring turf density back to its early summer form.
• Fall fertilizer helps regenerate roots lost by hot, humid or dry summer weather.
• Fall fertilizing fortifies your lawn so it can better combat severe winter conditions that lie ahead.
• A good feeding fills up your lawn’s gas tank before going dormant. That way it has plenty of energy stored for a healthy start next spring.

When To Fertilizer Your Lawn in the Fall

The best time to apply your last fertilizer application is between August 15 and October 1. Ideally, your last lawn feeding should take place six to eight weeks before the average first frost in your area. So, if this date is Oct 10, like it is in Minneapolis/St. Paul, you should target August 15 to September 1 as your last application. If you live in Des Moines where the average first hard frost is October 27, then you’d want to target your last fertilizer application six to eight weeks earlier, or between September 1 and Sept 15.

Planning fall fertilizer applications around average frost dates gives your lawn plenty of time to absorb all of the nutrients before it enters its dormant stage. There’s no need or benefit to carry over nutrients through the winter.

If you apply fertilizer too late, you’re making your lawn stay up past its bedtime when all it wants to do is go to sleep for the year. Late fertilizing of cool-season lawn grasses will keep it actively growing when frigid weather, snow and ice usher in winter, potentially causing winter kill and disease issues next spring.

What Fertilizer To Use in the Fall

The answer here depends on local ordinances or state laws. Some states do not allow the use of lawn fertilizers that contain phosphorus (the middle number*). Even though phosphorus is critical for root growth during seed and sod establishment and in the fall to assist in root redevelopment, many soils naturally contain phosphorus so it’s not necessary to apply more.

If you live in a phosphorus-free community, use fertilizers containing readily available nitrogen sources (the first number) and a fertilizer higher in potassium (the third number). This will properly feed your lawn going into winter. Good numbers would be 24-0-12 or 21-0-21.

If you live in a municipality or state where fertilizers containing phosphorus are allowed, this can add another layer of plant health protection to prepare your lawn for a harsh winter. A good example would be 24-5-10 or 20-5-20. A lawn starter fertilizer, such as a 14-14-14 or 12-24-12 would also work.

Liquid or soluble fertilizers containing similar NPK ratios can also be used. However, understand that recommended application rates of sprayable lawn fertilizers will deliver fewer nutrients per application compared to granular products. But, using a hose-end sprayer to apply a fall fertilizer is still an acceptable method of application. You may have to apply two applications a couple of weeks apart to realize its full benefit.

*Fertilizers come with an NPK number. N for nitrogen, that encourages green, leafy growth; P for phosphorus, which contributes to root development; and K for potassium, that helps maintain vigorous growth.

How to Fertilize Your Lawn in the Fall

Approach your fall fertilizer application just as you would any other. Follow the coverage recommendation for the chosen product. It’s always a good idea to split the application in half and then make two passes in different directions. For example: if your fall fertilizer bag says it will cover 5,000 square feet, find the setting on your spreader for 10,000 square feet (5,000 x 2). This will close the spreader gate allowing only one-half the recommended rate to flow through. Then make two consecutive passes at this spreader setting. This will apply the total recommended amount using two passes instead of one. This ensures even, uniform coverage, reducing the risk of missing parts of your lawn.

After you’ve finished your fall fertilizer application, make sure you thoroughly wash your spreader. This removes any remaining fertilizer residue that can corrode spreader components over the winter. Refer to your owner’s manual for additional recommended maintenance before winter storage.