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Management Updates: Apr 11, 2017

Spring Fertilizer Application Timing
Apr 11, 2017

Evolving nutrient management regulations in Massachusetts and beyond have brought increased focus on turf fertilizer programming and fertilizer applications. A primary goal for any turf fertilizer program is to time maximum nutrient availability to coincide with periods of peak turfgrass growth. In the spring, the window of ideal growing conditions is relatively short – sandwiched between the recession of winter and subsequent recovery, and the arrival of hotter, drier conditions that bring summer-related stress and associated growth and management challenges.

The start of spring growth... Here and now, Marathon Monday is less than a week away in Massachusetts, The Masters just wrapped, the fertilizer ads are heavy on the radio and TV, and we're into our second round of great spring weather (the first arrived in... February?). These influences make the appropriate timing for that first spring fertilizer application a popular topic of conversation.

After the average New England winter, time is one thing that a turf system needs after the snow melts and the soil begins to thaw. From a nutrient perspective, water must be free and in liquid form for nutrients to be mobile in soil and available for plant uptake. Fertilizer applied too early, when soil has not thawed completely and/or stand density has not recovered sufficiently from winter shoot dieback, has a much greater potential of being carried out of and away from the turf system with runoff.

Roots also need to be active and viable for nutrient absorption to occur. Harsh winter conditions also cause roots to die back, therefore a degree of root system recovery should take place prior to fertilizer application. The physical passage of mineral nutrients from the soil into root tissue, furthermore, is a largely active process for which energy is required. This means that photosynthesis and other biological functions must be up and running to adequately supply this energy. Nutrients in the soil solution that are not taken up promptly may be subject to loss through leaching and lateral movement.

The simple solution to promote robust plant uptake and minimize loss is to wait to fertilize in the spring until growth is solidly established, with the minimum threshold being the point of approximately 50% green-up. Contrary to what some believe, fertilizing early will not stimulate earlier growth; the onset and acceleration of both shoot and root growth are largely temperature dependent. Also, the calendar is never really useful in this regard, because of often significant year-to-year variation (at this time in 2012, Boston had 110 growing degree days; this year as of this writing, 47). Further variation can be introduced by many factors including geography, ambient temperatures, soil temperatures, soil moisture levels, exposure, etc. While sunny sites on the Cape may be about ready, for example, sheltered locations in the Berkshires may need significantly more time. The progression of aerial shoot growth and green color (see photo above right) are built-in signals that account for all of the above factors.

It is important to remember and keep in perspective that the aim is to maximize plant uptake while simultaneously minimizing nutrient loss from the system. Nutrients lost to the environment, most notably nitrogen and phosphorus, have a much greater potential of reaching and accumulating in ground and surface waters and negatively impacting the environment. In addition, nutrient loss is wasteful of limited time, labor, fertilizer, and financial resources. Nutrients that leave the system will not support the desired response in the turf, and may lead to performance and management problems and increase the need for future inputs.

For a final, related tip, don't let combination products be the boss when it comes to application timing. While the intent of fertilizer/pest control combination products is to 'kill two birds with one stone' for the sake of efficiency and convenience (fertilizer and pre-emergence herbicide, for example), the timing for one objective may have to be compromised in support of getting the correct timing for the other objective. If the compromise will be significant, opt for separate fertilizer and pest control applications for greater accuracy and control.

Submitted by: Jason Lanier