By Steve
Thomas, Nature Safe Specialty Products Manager
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.