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BY ROB GOLEMBIEWSKI, PH.D., AND LAURENCE MUDGE
As spring approaches, it's never too early to start thinking about rejuvenating lawns and getting then ready for the summer. Lawns are classified as being either cool season or warm season, depending on the turf species. Understanding which types of lawns you service, and your location, will dictate the type and timing of cultural practices you implement. Below are general recommendations for managing both cool season and warm season lawns this spring.
Cool season lawns
Renovation is a useful tool for improving weak lawns or those with damaged areas. Renovation typically occurs in the spring or fall, during favorable growing conditions; however, in the transition zone, cool season turf renovation usually occurs in the fall. Partial renovation can be as simple as overseeding a thin turf area. It can include power raking if thatch is greater than one-half inch, or core aeration if the soil is compacted. Total renovation involves taking out the existing turf prior to reseeding. If renovation is not done properly, the site might look good to begin with, but eventually will return to the conditions existing before the renovation. The key is to prepare a good seedbed and make sure there is good seed-to-soil contact.
Follow these steps to renovate a lawn without totally killing or removing existing vegetation:
—Adjust the height of cut down (scalp the turf) so as to reduce canopy competition for germinating seeds.
—Power-rake the lawn as many times as necessary to remove accumulated thatch and to expose approximately 50 to 70 percent of the soil surface. It is best to dethatch in multiple directions.
—If the soil is compacted, aerate the entire area to open up the surface and relieve compaction.
—Perform minor surface grading to eliminate high and low spots and to prepare the seedbed.
—Apply fertilizer and seed or sod as you would for a new lawn.
—Apply approximately one-quarter inch of organic mulch to enhance seed germination.
—Once seeded, manage as you would a newly planted lawn.
Total renovation involves killing undesirable grasses and weeds with a non-selective herbicide. Apply glyphosate (e.g., Roundup) in the spring, following turf green up. The effectiveness of the herbicide can be enhanced by skipping a mowing prior to treatment and applying it to actively growing turf. It probably will take two to three applications to kill creeping perennial grasses and weeds. After killing the grass, you have a choice of removing the dead sod or following the steps above under partial renovation. If you remove the sod, cultivate the soil and follow procedures for establishing a new lawn.
Aeration is the process of air exchange between the soil and its surrounding atmosphere. In the turf world, core aeration is the process of mechanically removing small plugs of soil from the lawn to improve natural soil aeration. Aeration has several benefits including:
—Improved air exchange between the soil and atmosphere.
—Enhanced soil water uptake.
—Improved fertilizer uptake and use.
—Reduced water runoff.
—Stronger turfgrass roots.
—Reduced soil compaction.
—Enhanced heat and drought stress tolerance.
—Enhanced thatch breakdown.
All lawns benefit from annual aeration. Heavily used lawns, or those growing on heavy clay or subsoil, may need multiple aerations each year. If you have a lawn composed of a cool season turfgrass like Kentucky bluegrass, tall fescue, or perennial ryegrass, both spring and fall are ideal times to aerate. Perform spring aeration during peak shoot growth, so the lawn recovers quickly from coring. In addition, aeration in the spring can reduce turf water use throughout the summer. Drum-type aerators (rentals) need two to three passes over the lawn to get the desired results.
It should be pointed out that spikers, machines that punch holes without removing cores, are of less value compared to aerators, because they compact the soil around the holes and do not increase the flow of water and nutrients into the root zone.
Mowing has greater influence on turf quality than any other practice. If you choose to do only one cultural practice, choose mowing and do it correctly. Frequent mowing at the proper height requires less time and effort than infrequent mowing. It also results in a healthy, dense, vigorous turf with fewer maintenance problems. The proper height of cut varies among turfgrass species. In general, mowing at a higher height allows for greater photosynthesis to occur, which translates into a healthier, denser lawn. The goal is to never remove more than one-third of the leaf blade during a single mowing. Most times of the year, mowing once per week is adequate. In the spring, during prolific shoot growth, mow more often.
Fertilizing, along with mowing and irrigation, is one of the basic cultural practices used to produce healthy, dense lawns. Unfertilized lawns tend to be thin, light green or brown in color, and have high weed populations. Adequately fertilized lawns look better than under-fertilized lawns, compete better against weeds, hold up better under wear and tear, and recover more quickly from damage.
Applying the right amount of fertilizer at the right time is important in maintaining a healthy, weed-free lawn throughout the year. Even if you prefer a low-input lawn, you will need to fertilize at least once or twice a year in order to maintain a relatively healthy lawn that can compete with most weed species and survive disease and insect infestations.
The ultimate goal is to apply the least amount of fertilizer needed to produce healthy turf and meet your personal aesthetic standards. The proper rate, frequency, and timing of fertilizer application depends on the desired turf quality, the type of fertilizer used, the type of turf species in your lawn, and whether clippings are returned to the lawn.
Fertilizer needs are lowest on older lawns growing in clay soils, where clippings have been regularly returned to the surface during mowing. However, if perennial ryegrass or Kentucky bluegrass is growing on imported sandy loam soil and clippings are removed, multiple applications of fertilizer may be needed to keep the lawn dense and attractive.
Nitrogen is the most important nutrient in most fertilization programs. Applied at proper rates, nitrogen stimulates vertical growth, improves turf density, and makes the grass darker green. By stimulating growth, nitrogen reduces the severity of certain diseases like red thread and rust. In the spring, apply a commercial fertilizer (1 lb. N/1,000 sq. ft.) which combines quick and slow-release nitrogen sources to provide a good initial and residual response and a lower burn potential.
Time the first fertilization of the year after the initial flush of spring growth.
Irrigation, despite being one of the most important factors in maintaining a healthy lawn, is the most often overlooked variable in lawn care. Proper irrigation avoids the negative effects of overwatering: excess foliar growth, nutrient leaching, shallow rooting, decreased wear tolerance, and reduced soil oxygen. In addition it increases succulence, compaction, thatch and disease activity. Underwatering can result in loss of color and density; reduced vigor; increased wilting; wear damage in traffic areas; and susceptibility to patch diseases.
When developing an optimum lawn irrigation schedule, you must account for the predominant turfgrass species and soil characteristics.
Nearby trees and shrubs that affect sun and shade, mowing height and potential for disease problems also need to be taken into consideration. The goal is to use the minimum amount of water necessary, and to apply it at the right time.
“How often?” and “How much?” are the two most common questions associated with lawn irrigation. A rule of thumb is to wait as long as possible in the spring before starting to irrigate. Once you begin, irrigate consistently so the lawn never turns brown between irrigation events. As fall approaches, try to reduce the amount and frequency of irrigation.
Please note that sporadic irrigation is not much better than not irrigating at all. In contrast, irrigating daily without regard for turfgrass water use produces lush, green lawns, but invariably applies too much water and forces excessive foliage growth.
Weeds most often become established in a weakened turf stand. It should be pointed out that weeds are not the cause of poor turfgrass performance but rather are a result of poor turfgrass performance. Certain weeds serve as excellent indicators of correctable conditions that have favored their development.
An effective weed control program includes identifying the weed(s) and degree of infestation; determining how the weed(s) was introduced; implementing sound cultural control strategies; imposing mechanical control strategies such as hand pulling or mowing; and, lastly, using chemical control (herbicides) if needed.
Numerous herbicides are available for controlling lawn weeds. Some are selective, which means they eradicate only the target weeds (examples include 2,4-D or dicamba). Others are nonselective, which means they eradicate all plants including grasses (glyphosate, for example). The selective herbicides should not be applied when temperatures exceed 80°F. Liquid herbicides usually are more effective than granular ones, due to more thorough coverage of plant leaves.
Once weed populations have been reduced to low levels, hand weeding can be a relatively effective way to keep populations low. This reduces the need for herbicides, often for many years.
Warm season lawns
In the transition zone and southern parts of the United States, warm season lawns can include bermudagrass, zoysiagrass, centipedegrass, and St. Augustinegrass. As the term warm season implies, these turf types thrive during warm temperatures, and can go dormant during cold weather. In the southern extremes, warm season lawns stay green year-round.
In areas where warm season lawns go dormant every winter, sometimes these lawns are overseeded with a cool season turf, primarily annual or perennial ryegrass. This cool season turf provides green color during the winter, and then dies when warm weather returns.
For non-overseeded dormant lawns, cultural practices should be followed as outlined above for cool season lawns, with the following exceptions: —Both renovation and aeration of warm season lawns should take place in the late spring or early summer when the turf is actively growing. Do not renovate or aerate in the fall.
—Mowing should be initiated in the spring, once the lawn has emerged from dormancy and top growth has exceeded your preferred height of cut.
—New preemergent herbicides for warm-season turf like Specticle Flo can be applied in the late winter to early spring to provide season-long grassy weed and selective broadleaf weed control. As with any pesticide, always read and follow label directions.
The fertility program depends on the warm season turf you have and where it is located. For example, St. Augustinegrass fertility requirements in South Florida will be different than a zoysiagrass lawn in Arkansas.
For overseeded lawns, the primary turfgrass species used is annual or perennial ryegrass which normally dies out in late spring, but if cool weather prevails, it can become persistent. The challenge for managing lawns overseeded with a cool season turf is transitioning from the cool season turf growing on top of a dormant warm season turf, to the warm season turf only. This can be difficult. If the cool season turf is allowed to persist into the late spring, this can weaken the warm season turf and not allow it to green up and grow as it needs to.
To discourage cool season turf, do not fertilize it in the spring. Once the warm season turf starts to green up, cutting back on water to put stress on the cool season turf can help as well. Sometimes the cool season turf will need to be treated like a weed and controlled with a post-emergent herbicide. Once the cool season is over, seeded grass is gone, and the warm season turf has started to grow, begin a recommended fertility program depending on the warm season turf you have.
Lastly, weed control in ornamental landscape beds should be addressed in both the spring and fall.
Preemergent herbicides like Surflan or Specticle G are applied prior to weed seed germination, and are used primarily to control annual grasses and selective broadleaf weeds, and generally are effective for three to six months.
EDITOR’S NOTE: Dr. Rob Golembiewski is a Green Solutions Specialist for the Environmental Science division of Bayer CropScience.
Prior to joining Bayer, he served as the Turfgrass Specialist at Oregon State University. Laurence Mudge is the Green Solutions Team manager for Bayer’s turf and ornamentals business. He has more than 22 years experience in the turfgrass industry.
In our February issue in the article “Making Your Controllers Smart!” we quoted John O’Donnell of Water- Logic as saying he was “...seeing about 40 percent water savings from the 1,000 or so Controller Link units.”
In his phone interview with our writer, he stated that “...we have more than 1,000 units using a similar technology placed on large commercial sites that are saving about 40 percent...”
We apologize for the mixup.