Expert advice about fertilizing a lawn, including how to fertilize a lawn in spring, summer, fall, and winter. How much fertilizer to apply and when to apply it.
In addition to proper watering (see Lawn Watering Tips), fertilizing a lawn is very important. When restoring a lawn, apply the fertilizer recommended by the results of your soil test. Use a slow-release fertilizer, and avoid putting down more fertilizer than you need.
When fertilizing a lawn, adding too much nitrogen can cause rapid growth and a thinning of plant cell walls, which makes grass more susceptible to disease. The excess fertilizer may also leach and eventually find its way into waterways, polluting them.
If you did not have your soil tested, apply a slow-release fertilizer with a nitrogen-phosphorus-potassium ratio of 3-1-2. Apply about 1/2 pound of nitrogen per 1,000 square feet of lawn.
The right dose of fertilizer won’t help much if your soil does not contain an adequate population of microbes—soil needs billions of these microscopic organisms per handful. Microbes not only digest grass clippings, dead grass roots, and stems, but they also make their nutrients available to living grass plants.
To have a thriving microbe population, your soil must contain 2 to 5 percent organic material. A top dressing of compost mixed with topsoil followed by aeration will incorporate some organic matter into the soil without disrupting the lawn. When top dressing your lawn, apply about 1 cubic yard, which is 100 pounds of a 40/60 mix of topsoil and compost per 1,000 square feet. Topsoil is available from most nurseries and landscape centers. Be sure it has a dark brown color and rich feel and that it has not been diluted with lighter colored subsoils.
Compost can be obtained from several sources. Many towns make compost available to residents at little or no cost. They make compost from the leaves, grass, and brush that residents haul to the dump. The compost should be screened to 1/4- or 3/8-inch particles, and it should be free of inorganic materials such as shreds of plastic leaf bags. Its moisture content should be 30 to 50 percent. Any drier, and the compost will release a lot of dust as it’s being worked; any wetter, and the material will tend to clump and not mix well with soil. Compost is also available from nurseries and landscape centers. Even better yet, make your own.
• Obtain a soil test to determine the grade and amount of fertilizer to use.
• Apply no more than 1 pound fast-release nitrogen per 1,000 square feet in a single application.
• Fertilize warm-season lawns from early spring until late summer.
• Most lawns need an average of 1 inch of water weekly for healthy growth.
• Cool-season lawns should receive most of their yearly fertilizer in the early fall. This will establish deep roots and help crowd out weeds in the spring.
• Use slow-release nitrogen whenever possible, especially on sandy soils.
• Wait until warm-season grass becomes dormant before fertilizing areas overseeded for winter color.
General Notes About Lawn Fertilization
• Use only the amount called for, based on your lawn’s square footage.
• For quicker application and to avoid a striped fertilizer pattern in the grass, use a rotary spreader, which applies fertilizer more evenly.
• Spread the fertilizer in two directions for each application.
• Apply fertilizer to dry grass, and water well immediately afterward.
• Sweep up any fertilizer spilled on paved areas and save for later use.
• Don’t use leftover lawn fertilizer on trees, shrubs, annuals, or perennials. Too much nitrogen on these plants stimulates stem and leaf growth and decreases flower and fruit production.