Late fall and early winter fertilization is a common and recommended practice in today’s turf management programs. As turf comes out of a stressful summer period, it is important to build the carbohydrate reserves to prepare the turf for winter. The accumulation and storage of carbohydrates is greatest during late fall and early winter because there is minimal shoot growth, yet good photosynthetic conditions. A pool of reserve carbohydrates is essential since it will serve as a source of regrowth and recovery during the following spring.
The roots of most cool season grasses continue to grow in autumn as long as the soil is not frozen. Cell division can occur in the root tips of cool season turfgrass at temperatures as low as 32°F.
Since it has been established that fall fertilization and dormant feeding are important in a fertility program, the question then becomes, “What fertilizer should I use?” When I was in a turf management class some 20 years ago, it was thought a good dose of synthetic nitrogen would be the optimum selection. It is true that the turf is in need of nitrogen at this time. Nitrogen is needed for shoot density, root growth and plant repair. Yet, excessive nitrogen in a soluble form will stimulate excessive shoot growth. This causes increased hydration of the tissue and decreases the carbohydrate levels in the plant. The result is decreased low temperature hardiness, making turf more prone to winter kill.
A more preferred nitrogen source would be in an organic form. Organic matter decomposition slows during cool weather, thereby slowing the release of nitrogen. An application of 1 to 2 pounds of N during this season provides the essential nitrogen needed, while keeping the nitrogen release rate at a minimum. There will be no flush of growth in the plant and carbohydrate levels will continue to increase.
It was once thought the use of organic nitrogen would be inadequate because the microbial activity in the cool season would be so low it would not mineralize the nitrogen. It has been proven through the research done at the University of Wisconsin by Dr. Wayne Kussow and by research conducted for Nature Safe by Dr. George Lazarovits of Agri-Food Canada that this in inaccurate. The reduction in biological activity in frozen soils will not impede the microbial activity needed to breakdown the organic nitrogen. This allows the fertilizer to work during the winter as well as in early spring. The nitrogen released when soil temperatures are above 32°F will be used for root cell division. When below 32°F, it will allow a reserve to build up in the soil that the plant can use immediately when it breaks dormancy.
We recommend two applications of Nature Safe during the fall. If you are aerifying in the fall, apply 1 lb. rate of nitrogen at this time. Nature Safe can get directly into the root zone and will improve the root density and length. If you are not aerifying, apply a 1 lb. rate of nitrogen in October. Apply the second application of 1 lb. of nitrogen as late as possible in the season (by the end of December). If aerifying, we recommend either 5-6-6 or 8-3-5. For the other applications, 8-3-5 or 10-2-8 make excellent choices. We have observed some of our most impressive results by using Nature Safe during this period. Our winter color has been excellent and our spring color has been outstanding. This method of fertilization allows the plant to get ahead start in the spring and be prepared for stress in the summer.