Most people apply a dose of lawn fertilizer in the spring, followed by one or two more applications during the growing season. If you are going to fertilize your lawn, do not do it too early in the season. The best time for that first application is late spring, just as the green grass is beginning to grow eagerly. In early spring, the grass is putting energy into root development. If you apply fertilizer too early, it will divert the plant's energy into leaf development too soon.
Debating the Use of Fertilizer on the Lawn
Whether or not you should use fertilizer on a lawn depends on where you stand on organic or low impact-to-chemical gardening practices. Organic gardeners bemoan the use of any chemicals as lawn fertilizers. The main concern is the fertilizer run-off can enter the local water supply. There is good evidence that shows phosphorus and nitrogen from lawn and agricultural fertilizers are contaminating streams, rivers, and groundwater supplies, creating a pressing environmental problem.
There are a few organic methods of feeding a lawn safely. You can choose to use a mulching mower that chops up grass into fine particles that then break down on the lawn. Horticultural experts say that throughout the season, this technique provides a lawn with as much nitrogen as one complete application of lawn fertilizer. You can also use organic fertilizers made from natural materials instead of refined chemicals. Organic-labeled fertilizers will indeed feed your lawn, though they are usually less saturated with the essential nutrients (nitrogen, phosphorus, and potassium) than the industrially refined fertilizers.
Traditional chemical lawn fertilizer remains the most popular choice and is widely available at hardware stores, big-box home improvement centers, and garden shops. These fertilizers come in many varieties. Some fertilizers match the season, such as early-season fertilizers, mid-summer fertilizers, and late-season "turf-builder" mixes. Other fertilizers are better suited for flowers or vegetables. Another category contains herbicides, which feeds the grass, kills weeds, and prevents weed growth.
Pre-emergent herbicides are a combination of fertilizer and crabgrass control herbicide applied in the early spring. This combination product does not have a full feeding of fertilizer. This small dose of fertilizer slightly boosts grass growth and keeps it alive, while the herbicide in the product restricts crabgrass seedling development.
Be Wary of Fertilizer Application Rates
Across the board, most fertilizer manufacturers are overzealous about their recommended dose and feeding schedule. Start light with half the recommended amount and rate of fertilizer. You can reapply if you don't like the results. Over a season or two, you'll get a clear sense of how much it takes to get a healthy lawn.
A healthy lawn will be a relatively light shade of bright green. A lawn that is a deep, almost blackish green, has been very heavily fertilized. The dark green color comes from a lot of nitrogen-based fertilizer used on the lawn. It is highly likely that some of that fertilizer has run off into the streets, storm sewers, and has made its way into local streams and rivers.
Determining the Best Times to Fertilize
Homeowners who prefer organic fertilizing methods might do a single "turf-builder" application in the early fall to build root systems. In the spring and summer, most may omit all fertilizers and rely on the nitrogen from mulched grass clippings to feed their lawn.
Homeowners using traditional fertilizer might want to apply two or three light applications per growing year—one in the spring, one at midsummer in regions where it is necessary, and one "turf-builder" application in the early fall.
The actual timing depends on your region and the type of turf grasses you have. For information on the best recommendations for your area, contact an expert at a local garden center or reach out to the nearest cooperative extension office.
Once you have figured out the best time, try to plan the fertilizer application with a short period of rainfall. If not, when you apply the fertilizer, you will need to supply your lawn with at least a quarter-inch of water. However, do not apply fertilizer before a massive storm. A rainstorm increases the risk of fertilizer nutrients flowing into storm drains and streams.
Maximizing Spring Application
If you fertilized your lawn the previous fall, especially late in the season, then the slow-release function of that fertilizer will help grass growth in the spring. Fertilizer manufacturers or lawn care companies may tell you to fertilize your lawn in early spring, but instead, consider the guidance by turf specialists and agronomists (soil experts) who say to hold off.
When cool-season grasses “wake up” in the spring, they enter a natural growth cycle when the root system begins growing and building carbohydrate (energy) reserves. Wait until the late spring (late May or early June) just before the heat of summer begins and after the grass is thriving before you fertilize the lawn.
Feeding your lawn at this point prepares the grass for summer. During the hot summer months, the grass will begin to slow down carbohydrate production and begin to utilize the reserves. Adequately feeding 3/4 to 1 pound of slow-release nitrogen will allow the grass to rebuild its energy (carbohydrate) reserves and ward off the stresses of summer, such as drought, heat, traffic, disease, and insects. A polymer-coated slow-release fertilizer can feed the grass for up to 12 weeks.
Feeding the Lawn in the Summer and Fall
Warm-season grasses thrive in the heat of the summer and can be fertilized throughout the growing season. However, cool-season grasses are in a survival mode during the heat of the summer. Refrain from applying fertilizer to a lawn in mid- or late-summer if you live in a climate where cool-season grasses are in your lawn seed mix. A cool-season lawn should need nothing other than water and pest management until September.
Most lawn experts recommend a mild dose of a "turf-builder" fertilizer formulation in the early- to mid-fall, while the turf still has several weeks of active growth before dormancy. This application will help build robust root systems going into winter and restart the growing cycle in the spring. You are not looking to return your lawn to the green of summer. Heading into winter, you can expect a natural slowdown of your lawn's growth and the loss of its green luster.
Nutrient Pollution, The Sources and Solutions: Agriculture. United States Environmental Protection Agency.
Grass Clippings, Compost and Mulch: Questions and Answers. University of Missouri Department of Horticulture.
Is Your Lawncare Stormwater-Friendly? Environmental Protection Agency.
Lawn Care Calendar. Washington State University Extension.
The Benefits of Late Season Fertilizer. Ohio State University, College of Food, Agriculture and Environmental Sciences.