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The best time to fertilize your lawn

Fall is the most important time to fertilize your lawn. Now is when roots grow.

Leaf on lawn in autumn. Photo by Auntie P.Fall is a great time to fertilize the lawn. Lawns are hungry now and they will develop most of their root systems during this season.

The timing of application(s) in fall is dependent on how you maintain the lawn (see Schedule below). 

All lawns benefit from an application in mid to late October. This is AFTER the turf blades stop growing and AFTER you have stopped mowing.

You won’t see an immediate response to this “Columbus Day” application, but it will make a big difference below ground. Roots keep growing until the ground freezes and this fertilizer will promote more root growth. Aboveground, this fertilizer will develop leaf shoots that will grow next spring.

Now is a good time to fertilize medium- and high-maintenance lawns. Lawns are actively growing now and this “Labor Day” fertilizer promotes vigorous blade growth and stronger root systems. 

A soil test is recommended to determine exactly what fertilizer your lawn needs. In most cases, a winterizer fertilizer is recommended. Formulations vary, but most winterizer fertilizers are approximately 25-3-10 (25% nitrogen, 3% phosphate and 10% potash). Winterizer fertilizers provide a little extra potash compared to summer fertilizers. This boost of potash promotes winter hardiness.

Fertilizers with slow-release nitrogen are valuable since they provide a consistent release of nitrogen to the growing plants. They are more expensive, however.

Follow the rates on the fertilizer package. A standard rate is 1 pound of actual nitrogen per 1,000 square feet. For reference, one pound of actual nitrogen is in four pounds of a 25% nitrogen fertilizer (such as 25-3-3). Excess nitrogen can burn the turf.

Reduced rates can be used in shady spots. They grow more slowly and only need about half as much fertilizer as sunny spots.

To prevent creating dark green stripes in your yard, apply half the fertilizer going back and forth in one direction and the other half going perpendicular to that. For example, apply half going north-south and the other half going east-west. 

Be careful about fertilizing in late September/early October. This “Indian Summer” fertilization can delay the hardening of the turf and make it more susceptible to winter injury.

For this reason, weed-and-feed fertilizers are not recommended. The most effective time to kill weeds (late September) is not a good time to fertilize the grass. Use a separate treatment to kill weeds.

Fertilization in early spring is not recommended. This stimulates leaf growth at the expense of root growth. The key to a healthy turf is a strong root system.

Water your lawn after fertilizing. This increases the effectiveness of the fertilizer and reduces the likelihood the fertilizer will run off due to a heavy rainstorm.

 

RECOMMENDED FERTILIZER SCHEDULE

Low-maintenance lawns: mid-late October.

Medium-maintenance lawns: late May, early September, mid-late October.

High-maintenance lawns: late May, July1, early September, mid-late October.

1Organic fertilizers recommended for summer applications. This application may be skipped if you let clippings fall and/or your lawn is more than 10 years old. Only fertilize in summer if you irrigate regularly. Do not fertilize if the lawn is dormant.

 

Sources:

Smith, R. and D. Herman. 2009. Turfgrass establishment and maintenance for home lawns and athletic fields. Publ. H1170. North Dakota St. Univ.: Fargo.

Stier, J.C. 2001. Lawn maintenance. Publ. A3435. Univ. of Wisconsin: Madison.

Written by Tom Kalb, Extension Horticulturist, North Dakota State University. Published in NDSU Yard & Garden Report, September 8, 2014. Photo was made available under a Creative Commons license specified by the photographer: Auntie P.

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