Fertilizer can give a lawn a boost, but knowing when to fertilize your lawn is vital for your grass to gain the full benefit of those vital nutrients. Feeding your turf at the right times through the seasons can result in fewer lawn weeds, less insect and disease issues, and better tolerance of drought and temperature extremes. This guide will help you build a simple fertilizer calendar that will help you save money and time, while giving you lush, healthy grass.
Start with a Soil Test
It is essential to know the nutrient composition of your soil before applying lawn fertilizer. Overfertilization is a common problem that has far-reaching adverse environmental effects, from groundwater contamination to degradation of waterways. Take time to perform a soil test through a reputable testing lab. Your local extension service can be a resource, and there are also several online soil testing companies.
A soil test will reveal levels of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg), along with soil pH. Turf grasses use large quantities of nitrogen (N) for growth, but there isn’t a reliable test for this nutrient. Timely application of a lawn fertilizer with the N-P-K ratio indicated by the soil test will supply ample nitrogen. Plan to have the soil tested every two or three years to maintain an accurate picture of your lawn’s nutrient needs.
Know Your Grass
The type of grass that makes up your lawn helps determine fertilizer timing by season. Lawn grass is divided into two groups: cool-season grasses and warm-season grasses:
Homeowners in moderate coastal climates and the lower Midwest might be growing cool-season or warm-season grass. But in general, if winter brings snow to your landscape, you’re probably growing cool-season grass, such as Kentucky bluegrass or tall fescue. These grasses have a soft texture and stay green late into the fall.
If you live in a region that doesn’t receive snow in the winter, your lawn is probably a warm-season grass, such as bermudagrass, St. Augustinegrass, or zoysiagrass. These grasses have a coarse texture and quickly turn brown in cool weather.
When to Fertilize Cool-Season Lawns
Only fertilize a lawn when it is actively growing. Cool-season lawns vigorously expand their roots and blades in spring and fall, making these the best times to fertilize them.
Spring
Apply a balanced lawn fertilizer as indicated by the soil test in spring after the second mowing. Use a slow-release fertilizer to limit excess growth and provide nutrients over the course of several weeks. Apply up to 1 pound of slow-release fertilizer per 1,000 square feet in spring.
Word of caution: avoid overfertilizing in the spring. A sudden influx of nitrogen will cause grass to grow fast at the expense of root health. Too much nitrogen in the spring can create a weak root system that isn’t able to withstand the heat and drought in summer.
Summer
Apply little or no fertilizer in summer. The lawn grows more slowly in summer and uses fewer nutrients. Drought and heat might push the lawn into dormancy. No amount of fertilizer will green up a dormant lawn. Fertilizing a heat-stressed or drought-stressed lawn can multiply the problem as fertilizer spurs the grass to grow, but it may not have adequate moisture to do so.
Fall
Cool-season grasses benefit most from fertilizer applied in the fall. Fertilizing helps the grass recover from the stress of summer by providing the necessary nutrients for root and shoot growth. Fertilizing in fall leads to a denser carpet of turf and prepares the grass for winter. Apply about 1 pound of nitrogen-containing fertilizer per 1,000 square feet two or three times at one-month intervals beginning in early fall.
Winter
Do not fertilize a cool-season lawn in winter. It is dormant and not actively growing. Fertilizing in winter is wasteful and harmful to the turf.
When to Fertilize Warm-Season Lawns
Always fertilize a warm-season lawn when it is actively growing. Generally, warm-season grasses grow when nighttime temperatures are above 70°F. The maintenance requirements and overall appearance of warm-season grasses are greatly influenced by the amount of fertilizer applied over the course of a year.
More fertilizer will likely bring about a higher quality lawn, but along with that carpet-like appearance comes higher water demands, more mowing, and in some cases, a greater susceptibility to pests and diseases. The recommendations shared here are for a low-maintenance lawn; it will look great but not demand a lot of extra attention.
Spring
Wait to fertilize in spring until after you have mowed the grass two or three times. Fertilizing a warm-season lawn too early is a surefire way to cause turf dieback and lawn trouble for months ahead. Bermudagrass, St. Augustinegrass, and zoysiagrass do well with a spring application of 1 pound of fertilizer per 1,000 square feet. Don’t fertilize centipedegrass and buffalograss in spring; they grow best with just one fertilizer application in the fall.
Summer
Fuel the rampant summer growth of warm-season grass by fertilizing Bermudagrass, St. Augustinegrass, and zoysiagrass with an additional pound of slow-release nitrogen-containing fertilizer per 1,000 square feet. Choose a slow-release formula to avoid surges of growth. Just like in spring, don’t fertilize centipedegrass and buffalograss.
Summer fertilizer is not essential for good growth; warm-season grasses can easily be maintained with a spring and fall fertilizer application. Fertilizing in summer will result in a greener lawn, provided rainfall is adequate. If drought conditions develop and warm-season grass goes dormant in summer, do not fertilize. Fertilizing dormant grass can kill the turf.
Fall
Fall is the most beneficial time to fertilize warm-season lawns. If you can only fertilize your turf once a year, do it in the fall. Applying lawn fertilizer in fall spurs warm-season grasses to increase density, which helps them resist winter weeds. Fertilizing in the fall also improves the color of the grass and prepares the turf for strong growth in spring.
Make a fall application of 1 pound of fertilizer per 1,000 square feet of lawn at least six weeks before frost is expected. The turf needs this lead time to absorb the nutrients before growth ceases in winter. Use a water-soluble or quick-access form of nitrogen.
Winter
Do not fertilize a warm-season lawn in winter.