Aside from measurable snow throughout the state mid-week, one of the most noticeable developments in the spring landscape has been the rapid transition of turf areas from shades of brown to increasingly vibrant green. This green up for many shifts attention to the topic of fertilization, for which correct timing in the spring increases the likelihood of optimum results.
Carefully-timed spring fertilizer applications can provide a nutritional boost to get the jump on summer annual weeds, along with supporting the allocation of reserve resources for weathering the upcoming summer stress period. In the spring, the ideal approach is to attempt to synchronize maximum nitrogen (N) availability with the peak growth period to promote vigorous root and shoot growth. Of the essential nutrients required by turfgrasses, N has the greatest effect on growth and development and therefore comprises the basis of most fertility programs. Potassium (K) can be applied in balance with nitrogen (a rate of 1/3 to 1/2 the N rate is a good general guideline) and phosphorus (P) is rarely needed for established turf on most New England soils unless deficiency is indicated by a soil test.
The N release characteristics of the fertilizer material are a particularly important consideration for precise application timing. Many fertilizers are formulated with a certain percentage of the total N in a form that is quickly available to the plant (most often referred to as water soluble nitrogen, or WSN), and another portion that is in slow-release form. The readily available N helps to meet the more immediate needs of the turf and produce a short term response, and the slow-release N provides a longer residual and ongoing maintenance of the plant-available nutrient pool.
The first seasonal peak of growth varies depending on factors such as location or prevailing weather conditions, thus the timing of spring fertilizer applications should adjusted accordingly. The variation in Massachusetts is such that sunny sites in the Southeastern part of the state may be ready for fertilization at this time, while it may be a little while yet for shady spots in the Berkshires.
If fertilizer is applied too early, nitrogen (especially water soluble N) and phosphorus can be carried off-site with runoff, especially when the ground is still frozen. Even in instances where soil has thawed, nutrients applied prior to a sufficient break in dormancy can leach below the root zone before plant uptake occurs. Nutrient loss from the turf system translates to waste of management resources and a significant increase in the potential for adverse environmental impact. Nitrogen and phosphorus in the environment can contaminate ground and surface water, and fertilizer use is currently being addressed in pending regulations for which the intent is to protect water quality.
Root tissue must be active, nutrients must be in the soil solution and transpiration must be up and running for nutrients to be absorbed by turfgrass plants. Outside of specialized programs, therefore, it is typically best to wait until growth resumes in earnest before fertilizing in the spring. A frequently cited minimum threshold is the point of approximately 50% green up. On the other end of the spectrum, fertilizing too late diminishes benefits that can be realized before hotter and drier conditions set in. To avoid disruption of summer pre-conditioning, fertilizer applications later in the spring should include larger percentages of slow-release nitrogen.
Submitted by: Jason Lanier