The misconceptions regarding spring fertilization
Paul Pugliese says that warm spring weather can go to the heads of homeowners and landscapers alike, and that can be deadly for the turf they manage. The natural tendency is to rush out and heavily fertilize grass during the warm spells of March and April, but the practice may be more conducive to growing weeds than the health of grass.
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There are a lot of misconceptions about turfgrass fertility in Georgia and elsewhere in the South, and as the weather warms up they pop to the surface. The primary problem is that early nitrogen (N) applications can lead to premature turfgrass green-up and subsequent problems.
Every spring, Pugliese, who is the University of Georgia Agriculture and Natural Resources Cooperative Extension agent for Cherokee County, sees even experienced landscapers, turfgrass managers and maintenance companies applying nitrogen fertilizers so early that it pushes the grass out into a growth cycle that will likely be interrupted by a late freeze. A scarcity of soil testing exacerbates the problem, with grass, at times, being fertilized with nutrients it doesn’t need, at least at this point in the season. He says that two factors cause landscapers to jump the gun this way: One is the plethora of spring advertising for popular weed-and-feed products that often contain nitrogen, and the other is that homeowners and other clients push the landscapers to green up their lawns as early as possible.
Clint Waltz, an associate professor and turfgrass extension specialist for the university, seconds Pugliese’s observations. He says that when landscapers and their clients “get a little excited” about springtime weather they should step back and consult the experts on this topic, because the early application of nitrogen can be downright harmful.
“It’s just the wrong time to be putting that out,” Waltz says. He notes that University of Georgia guidelines are to not apply nitrogen to warm-season turfgrass until springtime soil temperatures at a depth of 4 inches are 65 degrees and rising. It is best to put out weed-and-feed fertilizers that don’t contain nitrogen prior to soil temperatures reaching 55 degrees, or by March 15 in most parts of Georgia, but those are preemergence herbicides with some non-nitrogen fertilizers added.
That’s where much of the confusion comes in, because so often the common weed-and-feed amendments come in one package. Waltz points out that over the last five years, more and more weed control packages have been released with no nitrogen added. Those are the ones that can be used early in the spring for the preemergent control of weeds.
There is also confusion about the different treatments for warm and cool-season grass species, Waltz says. Cool-season grasses—tall fescue is a common one in the Atlanta area—may actually need some nitrogen early. They will need it to take advantage of the early growing season that warm weather offers.
It is the warm-season grasses, St. Augustinegrass, bermudagrass, zoysiagrass and centipedegrass are all common in Georgia, that require the 65-degree soil temperatures and the assurance that temperatures will continue to rise, rather than fall. Landscapers and turf managers who don’t have their own soil temperature probes can access local weather station data at www.georgiaweather.net, which is the site for the Georgia Automated Environmental Monitoring Network. Soil temperatures at different depths are available there, and landscapers in other states that have the problem of early turfgrass freezes can access their own states’ data on similar sites.
“Or, they can go get a soil temperature gauge and test it themselves,” Waltz says. Timing is everything. Warm-season grasses can receive the proper amount of nitrogen precisely when they need it. For St. Augustinegrass and bermudagrass, which need about 4 pounds of N per growing season per 1,000 square feet, the first pound could be applied when that 65-degree threshold is reached, typically in May. The other 3 pounds could be applied 1 each month in June, July and August.
Zoysiagrass, on the other hand, needs only 2 pounds of N annually, so half a pound could be applied in May after all danger of frost has passed, and half a pound each during the next three months. Centipedegrass is a very low nitrogen user, needing only 1 pound per season. Thus, .25 pound each over the four-month period would be appropriate. Another Web site, www.georgiaturf.com, has calendars that can be applied to each grass species. This is the University of Georgia’s turfgrass site, and it is loaded with other good tips for management.
The important part to remember is to avoid putting those warm-season grasses in danger too early, because in Georgia a freeze can often occur around Easter or later. Waltz says the cold damages leaf tissue, with the food storage capabilities of the plants being depleted. That can lead to turfgrass with less vigor throughout the growing season, and it can actually kill the more susceptible centipedegrass.
“It can delay the onset of true green-up,” he adds. He also agrees with Pugliese on the subject of weeds. If warm-season grasses are dormant when fertilized, the nitrogen will simply encourage weed growth. Weeds will then have a head start on the grasses once they come out of dormancy. Cool-season weeds, such as chickweed, will then die off at the onset of heat and leave bad spots in the lawn. Waltz doesn’t recommend weed control during green-up for that reason; just let the winter weeds die off naturally, and then apply herbicides to warm-season weeds, like plantain and crabgrass, as they pop up later.
In addition, Waltz says, warm-season grasses can be made more susceptible by nitrogen to spring diseases such as large patch, a fungal disease common in Georgia and throughout the Southeastern states. Dollar spot can also be promoted, and earlier injury from spring dead spot can manifest itself. A rainy spring can make these diseases worse. Instead of early green-up, that application of nitrogen could cause an unsightly and unbalanced lawn.
One key to the proper application of fertilizer is soil testing, Waltz says. Ideally, that should be done in late fall/early winter. At that time, look more for deficiencies in potassium and phosphate, as well as micronutrients. Those deficiencies should then be made up in the spring as the soil turns 65 degrees at 4 inches, and nitrogen deficiencies made up at the same time. If applied before that, select a zero-nitrogen product.
The other factor to look for in a soil test, especially in Georgia where the soil tends to be a little acidic, is pH levels. If the fall/winter soil test shows acid soils, an amendment of a product like dolomitic lime should be applied, but since lime takes some months to leach down into the rootzone, apply it early in the winter so that the soil pH adjustment will occur by the beginning of the growing season in May.
Another good service that landscapers and turfgrass managers could perform for their clients is to educate them about the dangers of early nitrogen application and caution them to read the labels of the products they might want to apply. This could avert some prominent turfgrass problems and blunt the tendency of clients to rush out at the onset of warm weather and begin feeding their grass all sorts of nitrogen-rich products.
Don Dale resides in Altadena, Calif., and is a frequent contributor to Turf. He has covered the green industry for more than 10 years.
