Late Fall Fertilization

The turf management practices we follow in the fall play a major role in the quality of turf next spring.  Fertilization, cultivation, overseeding and special projects are some of these practices. 
 

Timing of Late Fall Applications: Both early fall and late fall fertilization should be considered.  Fall fertilization is best done during late August and early September and then again in late october.  With the weather changes in late summer - shorter days, cooler nights and more regular rainfall - the grass plant tends to grow stronger than occurs in the spring.  This results in improvement in turf density after the rigors of summer.  So fertilization in the fall deserves top priority.  More of the carbohydrates manufactured by photosynthesis at this time of year will be stored, building up the plant for next year. 

Normally it is best to withhold nitrogen applications during mid September to the third week in October to permit the turf to "harden off."  If not applied earlier, low rates of N (1/2 lb. N/1000 sq. ft. or less) can be applied as needed to hold reasonable color and density.  This can help improve turf density and permits the turf to accumulate carbohydrates.  Heavier rates of N in early October should normally not be used as this could cause the grass to be come very succulent.  If a high rate of N is applied in late September or early October with excellent growing conditions (warm and rainy) and then is followed by a hard freeze, the grass leaf tips could be killed, reducing the potential for photosynthesis at this time of year. 

The most important objective of late fall nitrogen fertilization is to supply nitrogen to the turf after growth has ceased but when photosynthesis can still occur.  This will normally take place anywhere from the last week of October  to the second week of November.  It will vary with the particular year by as much as two weeks. Some additional short growth spurts may require mowing after that time, but regular mowing is no longer necessary. At this time the root system is still active since the soil is warmer than the air.  Nitrate nitrogen can still be taken up and utilized by the plant. 

If proper nitrogen fertilization has been practiced during the fall period (September), the turf should still be green and physiologically active in the late fall.  This permits the plant to continue photosynthesis whenever modest 
temperatures and some sunlight conditions occur. Carbohydrates manufactured during this time are not "burned off" with growth and clippings, but are stored.  This builds up the plant for next year which permits root growth initiation in the spring even before top growth begins. 

Late fall fertilization also reduces the need for early spring fertilization which 
tends to enhance growth and mowing requirements at a time of year when growth is likely to be very rapid anyway. Carbohydrates lost with the clippings in the spring are obviously no longer available to the plant.  It makes sense to hold those carbohydrates in the plant as long as 
possible.  As the hot weather of summer comes the carbohydrates will be lost readily.  Keeping the carbohydrate level in the plant high enhances summer stress tolerance, keeps some reserves in the plant for recovery of 
turf density if needed and may reduce the rate of root loss during the summer. 
 

Nitrogen Carrier: 
The choice of carrier is very important with late fall nitrogen fertilization.  To accomplish the objective of getting a significant portion of the applied nitrogen into the plant right after application necessitates that the 
major portion of the nitrogen be from fast acting, soluble sources.  Some of the nitrogen can be slow release, as much as 25% or so.  This slow release carrier will provide a small amount of N next spring, but will not result any 
major response or flush of growth.  Any of the slow release carriers should be acceptable for this portion of the fertilizer as long as the rate of N release is not dependent on high soil temperatures. 

Benefits of late fall nitrogen include good carbohydrate levels in the turf the next spring, good early spring root growth, good fall and spring color and good turf density so there is less potential for establishment of spring weeds. Since root growth of cool season grasses begins before top 
growth, it essential that a high level of carbohydrates exist in the plant to initiate that root growth.