November 5, 2012
University of Arkansas, Division of Agriculture
Turfgrass Science Program (http://turf.uark.edu) – Turf Tips
Fall Fertilization for Cool-Season Lawns
Tall fescue and bluegrass lawns throughout Arkansas are currently looking their best (see photo at right), as cool temperatures and shorter fall days are ideal conditions for these grasses to thrive. These cool-season grasses have two seasons of active shoot and root growth, including the fall period and then again in the spring (see figure below). As the turf goes into the fall period, it is producing abundant new roots and tillers and this is the growth period that is most favorable for fertilization with nitrogen. Nitrogen fertilization in the fall will recover the turf from the difficult summer period and will also be the foundation for spring growth as well.
Over the years, there have been countless research studies that have demonstrated the value of fall fertilization of cool-season grasses. However, most homeowners will usually only provide a good shot of fertilizer early in the fall period, when temperatures first cool, and they forget about the importance of late fall fertilization on cool-season grasses. We currently recommend that approximately 75% of the nitrogen fertilization that a bluegrass or tall fescue lawn receives during the growing season be applied during the fall, and over half of that fall application should go down late in the fall season, as the turf stops growing, but conditions remain favorable for the plant to photosynthesize and capture energy. Although the turf will not produce a lot of new leaf growth from a late fall fertilization, this application will continue to stimulate root production, enhance storage of carbohydrate reserves, and even initiate new buds that will grow in the spring of the year.
There are some other benefits of late-fall fertilization that are easy to see in the turf performance. One of the benefits of late fall fertilization is that the turf will have ample stored reserves to grow in the early spring without additional fertilizer. Typically, we do not see the need for additional nitrogen on cool-season lawns in the spring until mid-April or early May. When nitrogen is applied in early spring, the lawn will typically go into an accelerated growth cycle and this will increase the mowing frequency on the lawn. A second benefit from late-fall fertilization is the effects on winter color of the lawn. We routinely see a significant increase in winter color on the lawn when we apply nitrogen late in the fall compared to the same amount of nitrogen applied early in the fall (see photo below).
Although many fertilizers are available to homeowners for fertilization of their lawns, we typically recommend a soluble source of nitrogen be used for the late fall application. The reason for this is that many slow-release fertilizers need soil microbial activity to release and cooler soil temperatures late in the fall may reduce microbial activity and the nitrogen may not be available for plant uptake until the following spring when soils warm again. Sources to consider for late-fall applications include ammonium sulfate (21-0-0), urea (46-0-0), or ammonium nitrate (34-0-0). Rates should be in the 1-2 lb. of N per 1000 sq. ft. regardless of the source. If you have been fertilizing your lawn with nitrogen for several years, consider using the lower end of our N recommendation. Well-maintained, mature lawns tend to accumulate soil organic matter, which is a good source of nitrogen throughout your lawn's growing season and will lower the N needed through fertilization.
Finally, what is the best time for this late fall application? We generally recommend that this application be made at the point when the lawn no longer needs to be mowed. This can obviously vary depending on where you are in Arkansas and the weather conditions for the fall, but a good target date is somewhere during the last 2 weeks of November in north Arkansas and first 2 weeks of December in central Arkansas or farther south. I always think it is a great way to walk off a few of those Thanksgiving calories.
If you have never put down nitrogen this late in the fall on your fescue or bluegrass lawn, we encourage you to give it a try and see how you like the results. Best wishes for a happy Thanksgiving with friends and family…
Mike Richardson and Doug Karcher