Why Proper Turf Fertilization is Necessary
Turfgrasses are one of the most populous plants used in our landscape and they are forced to grow on some of the worst situations. High demands are placed on these energetic plants that make up the carpet of our lawns. These tough grasses are required to hold a rich green color spring through fall. They must stand up to foot and vehicle traffic like no other plant. We ask them to be soft on our children’s bare feet and durable against our pets’ claws. We require all of this be accomplished on top of nutrient poor, stripped, and compacted urban soils. For a look into soil science and characteristics of urban soil see: https://www.ces.ncsu.edu/fletcher/programs/nursery/metria/metria05/m57.pdf
To satisfy the many demands, while growing on less-than-ideal sites, these turfgrasses can use a little support. There are many ways we can aid these important plants in our landscape. One is provision of nutrients through adequate and timely fertilization. The primary, and often lacking, nutrients are Nitrogen, Phosphorous, and Potassium. These macronutrients allow for consistent leaf and root development and maintenance of that soul-satisfying green color.
The highest used macronutrient, nitrogen, is an important component of photosynthesis, the sugar-production system necessary for all plant growth. When nitrogen is limited, the turf grows very slowly and loses the fresh look and feel. Nitrogen is a highly mobile nutrient moving quickly down in the soil profile out of reach of grass. Most urban soils are severely lacking organic matter which is a key source of resupplying nitrogen. For this reason, it is necessary to make multiple fertilizer applications per year or utilize high-quality, slow-release products to ensure adequate nitrogen is available throughout the entire growing season.
The second macronutrient, phosphorus, aids in cell development and new tissue growth. Phosphorous is often present in the soil in sufficient quantity though it can be bound tightly to clay particles making it unavailable to the plants. This can be a particular problem in acidic soils. Though phosphorus is necessary for turfgrass, in Minnesota it is banned from use in turf fertilizer programs due to the harm runoff causes in waterways. However, special permission to use phosphorous is granted if a soil test proves it is severely lacking. See http://www.mda.state.mn.us/phoslaw for more information.
Potassium is the third most used nutrient by turfgrasses. Potassium is required in several plant processes, including photosynthesis and regulation of the stomates which are part of the plant respiration system. Potassium is integral for providing disease resistance, drought tolerance, and cold hardiness in turf. In spite of the abundance of potassium in the soil, little of it is available to the plant. Unavailable soil-potassium is locked up with other minerals. A soil test can help determine the amount of usable potassium (ionic K+) and inform the fertilizer program.
Fertilizer products display the ratio of the three macronutrients on the front of the label. This is the guaranteed analysis which tells the percentage of each macronutrient in the product. The first number is the percentage of nitrogen, the second is potassium, and the third is phosphorous. If micronutrients (iron, boron, magnesium etc.) are included they are listed separately on the label.
In addition to different guaranteed analyses, fertilizer formulations are quite variable. Some fertilizers include post or pre-emergent herbicide. If these are used, Minnesota law requires chemical postings during application. Some fertilizers are synthetically produced, these simply contain the stated nutrients. Organic fertilizers are composed of biological organisms and nutrients within composted organic matter. Regardless of the formulation, all fertilizer products display the guaranteed analysis to assist in calculating application rates.
Fertilizer application type also varies between products. Liquid fertilizers are immediately available to the plant and are applied at the highest frequency. Uncoated, granular products release the nutrients over a few weeks. Slow-release granular products release the nutrients over a couple of months. The specific formulation, application method, and rate varies dependent upon many factors including: grass varieties in the turf, presence or absence of irrigation, soil structure and condition, as well as the use and aesthetic requirements of the lawn.
The rugged little plants that are integral to our landscapes have been asked to show their best on our worst sites. “Dollar for dollar fertilization does more to improve poor-quality turfgrass or to maintain good-quality turfgrass than any other management practice.” (http://plantscience.psu.edu/research/centers/turf/extension/factsheets/turfgrass-fertilization-professional#pit. ) If we do a little to help the turf perform by providing supplemental nutrients, our turfgrasses will be well suited to stand up to all our needs. Below are photos of the stark visual difference between fertilized and unfertilized turf.
Photos Courtesy of Jake Louwsma, taken May 2017
For a deeper look into how to build a fertilizer program and calculate application rates see this information from PennState:
If you are looking for site-specific recommendations, contact your state’s extension service.
By: Catherine Nickelson, B.S. Horticulture, University of Minnesota; ISA Certified Arborist