The nitrogen used should be a quick-release nitrogen (N) fertilizer with a small amount or no phosphorus (P) or potassium (K). Ammonium sulfate (~21% N), ammonium nitrate (33%N), and urea (~46% N) are ideal as they do not contain P or K. Slow-release products are not appropriate at this time of year. Two pound of N should be applied over every one-thousand square foot area of lawn. This recommendation means applying about ten pounds of ammonium sulfate, six pounds of ammonium nitrate, or four pounds of urea per one-thousand square feet of lawn. The goal is to provide a quick source of nitrogen to increase rooting depth and increase carbohydrate storage. This creates a healthier lawn more resistant to winter, spring, and summer disease and insect pests. If your lawn is a warm-season grass such as buffalograss you are out of luck as this procedure does not work on these grasses. If your lawn is Kentucky bluegrass, tall fescue, or perennial ryegrass applying two pounds of nitrogen at this time of year is what you should be doing.
Watering is critical to dissolve the fertilizer and move it into the roots of the grass. If your soil is the typical silt clay loam common to the valleys of western Colorado you should water your lawn for fifteen minutes if you have pop-up spray sprinklers, or fifty minutes if your sprinkler system has impact or rotary stream nozzles. Split these times in half with an hour between each watering to ensure the water penetrates the soil and doesn’t run off the lawn.
To learn more about this Late Season Fertilization program go to my web page at: http://www.coopext.colostate.edu/TRA/PLANTS/turf-lsf.shtml.