By Rachel Vecchio, Master Gardener 2016 Intern
and Libby Good, Certified Master Gardener
THE REALITY: A homeowner’s lawn and garden spring to-do list is usually long, including getting out the fertilizer and putting the spreader to work. But that particular chore may be unnecessary and even harmful, according to experts.
First and foremost, if the lawn appears healthy and is well-established, fertilizing regularly is optional. Fertilization is really only necessary when a lawn has been damaged, such as through disease or poor growth and quality. However, to determine the lawn’s fertilization needs, perform a soil test before applying fertilizer. The soil test will indicate the amount of calcium, magnesium, phosphorus and potassium the soil can provide turfgrass. While a soil test does not evaluate nitrogen requirements, results will include a recommendation for nitrogen based on the variety of grass being grown.
Conducting a soil test every three to four years is crucial when it comes to fertilization. Soil test kits are available at local Virginia extension offices and Master Gardener plant clinics. Without this test, the homeowner likely will not know what to apply and how much (assuming anything is needed at all) and could over-fertilize, which can lead to damaging runoff and groundwater effects, particularly in states that are part of the Chesapeake Bay watershed.
Once the lawn’s fertilizer needs are known, the question becomes when to apply the fertilizer. Current research indicates that autumn (October) is the best time to fertilize cool season turfgrasses, such as Kentucky bluegrass, tall fescue, perennial rye grass and fine fescue. Warm season turfgrasses, such as zoysia grass and Bermuda grass, may be fertilized in very late spring (May-June). Therefore, there is no “one-fertilization-time-fits-all” approach.
In fact, fertilizing the lawn at the wrong time can hurt the turfgrass. Research shows that cool season turfgrasses undergo a spring root decline through which much of the old root system dies and the turf begins to grow new roots. During this decline, there isn’t a substantial enough root system to fully absorb the fertilizer’s nutrients. The nutrients that are absorbed are then put toward leafy blade growth at the expense of root growth. Without a healthy and well-developed root system, the turfgrass is susceptible to disease and poor growth. This is just one example of the damage that may be caused by applying fertilizer at the incorrect time.
To ensure a healthy lawn that is fertilized appropriately and with regard for the environment, it’s important to know what type of turfgrass is being grown – and always start with a soil test.
- The Best Time to Fertilize Your Lawn, North Dakota State University, 2014
- Carpenter, Daniel, Larue Hort Quarterly Newsletter, University of Kentucky Cooperative Extension, October 2016
- Fertilizing – Lawns, University of Maryland Extension
- Gill, Daniel and Thomas A. Merrill, Time to Fertilize Your Lawn, Louisiana State University, 2004
- Gillman, Jeff and Maynard, Meleah. Decoding Gardening Advice. Portland: Timber Press, 2012.
- Goatley, Michael Jr. et. al., Fall Lawn Care, Virginia Cooperative Extension, 2015
- Goatley, Michael Jr. et. al., Lawn Fertilization in Virginia, Virginia Cooperative Extension, 2015