No matter which procedure is chosen, or how severe the need for overseeding, step one in the process is to diagnose the cause of the decline of the field. This can be confusing, as it’s common for several factors to work together to cause injury. If the cause(s) is not determined, the turf is likely to decline again soon after the overseeding process is complete.
Step two is to solve the problem(s) that is identified as the cause of the thinning. Step three is to put the seed in the ground. Step four is to care for it afterwards. Unfortunately, it’s all too common for steps one and two to be skipped, resulting in disappointment from poorly performing turf.
Need to replace worn-out turf.
PHOTO BY JOHN C. FECH, UNL.
Reasons for overseeding
The three most common reasons for needing to overseed a field are thin turf, the opportunity to incorporate new cultivars for disease resistance and to repair winter damage. Other reasons exist as well, such as to change the color of the field, but just as important as diagnosing the cause of the original decline, being cognizant of the purpose for introducing new cultivars will help guide the product selection process.
Rip it up
If you’ve ever grown carrots or radishes, you know what it takes to secure adequate germination: sufficient moisture and good seed to soil contact. Preparing optimum conditions would result in a loose, rich soil medium in full sun. Most sports fields are in full sun, so that isn’t a limitation; however, creating an adequate seedbed can be a challenge, especially in older turf with a thick thatch and mat layer.
Thick thatch and mat layers.
PHOTO BY BRAD JAKUBOWSKI, DOANE COLLEGE.
Time constraints and tight event schedules often limit your opportunities to prepare the seedbed to optimum conditions, so alternative methods are required. When this is the case, your goal is to punch as many holes or cut in as many slits as possible for seed application. For example, when aerifying prior to seeding, your optimum goal is to finish with 2-by-2-inch or less spacing (if possible, 1 inch would be excellent) of the aerification holes. Depending on the equipment available, this may require making multiple passes in three or more different directions. The seeds that fall in these holes have the best opportunity to germinate and are provided the best protection from foot and equipment wear and tear. Topdressing with sand or a compost material (which can be from your local landfill) will increase the germination rate and help protect the new seedlings from variations in moisture and temperature as well as traffic.
At this point, do not hesitate to use seeding rates greater than the standard recommended rates. Don’t forget, your goal is to produce as good coverage as possible, and seeds will be one of your least expensive inputs. Research at Iowa State University has shown that rates as high as 50 to 60 pounds per 1,000 square feet of perennial ryegrass applied to high-traffic areas maintained effective coverage to the playing surface. Seeds that may not have germinated could prove to be useful in producing a seed bank for the future. These rates may seem a little high, so at the least consider doubling normal establishment rates to help ensure good coverage.
There are several pieces of equipment that can facilitate good seed to soil contact. Chatting with equipment distributors and other sports turf managers will provide the necessary information to tailor equipment offerings to the specific needs of the sports fields. In some cases, a “test drive” or the utilization of borrowed or rented equipment may be an option.
Growth from pregerminated divot mix.
PHOTO BY BRAD JAKUBOWSKI, DOANE COLLEGE.
Pregermination procedures – The day before a big game, make up a batch of overseeding mix. Start by tossing a bag of seed in a 55-gallon drum half full of water. Soak it overnight, and then hang it up to dry and allow the excess water to drain out. When drained, mix it 50/50 with sand or sand mix and fill up 5-gallon buckets. As soon as the game is over, hand each of your crew members a 5-gallon bucket full of overseeding mix and an empty 5-gallon bucket. Assign them to a defined area, such as between the goal line and the 5-yard line on a football field and ask them to walk from one sideline to the other, picking up loosened divots and dropping them into the empty bucket and dropping a handful of overseeding mix to fill the divot.
The pregermination routine will cut the time necessary for germination in half, or at least reduce it by 30 to 40 percent. This reduction may be all you need if the team goes out of town for a week.
Follow-up routine – Once the seed is in contact with the soil, four operations should be the focus of the follow-up routine. First, the application of starter fertilizer. Since existing turfgrass is present with most overseeding operations, starter fertilizer applications should be delayed until the new seed is actually up and growing. If made at the time of seeding or soon after, the starter fertilizer will encourage the growth of the existing turf rather than the new seed. Once an inch or two of the new shoots are visible, apply fertilizer; proper timing of this application will encourage both sets of turf plants to grow.
Proper mowing is crucial after overseeding. Once a majority of the new turf plants have reached a height above the established mowing height for the field, begin mowing. Mowing newly renovated areas is a double-edged sword, or at least has somewhat conflicting parameters. Keeping the turf within the bounds of the turf canopy will allow more light to penetrate and encourage the germination of the seed that didn’t grow in the first few weeks after seeding, as well as allow for adequate airflow over the leaf blades, which discourages the development of foliar diseases such as leaf spot and dollar spot.
The other side of the double-edged sword is that allowing the new plants to grow beyond the established mowing height will result in deeper roots than close-cut turf and increase the ability of the turf to compete with broadleaf weeds. Overall, the function of the field usually dictates which set of conflicting outcomes is more closely adhered to.
One material, siduron (Tupersan), is marginally effective against annual grassy and broadleaf weeds, with the efficacy in the 60 percent range. Sports turf managers should weigh the cost of the product against the likely outcome to determine if use of siduron is justified on their sports fields. A certain amount of weed suppression will result from normal mowing practices, which is also a factor to consider.
Research at the University of Nebraska indicates that a new product, Tenacity (mesotrione), has been shown to be extremely safe to apply prior to or over new seedings. It is also a good postemergence crabgrass control in sports fields. Tenacity is extremely safe on most turf species prior to reseeding and will effectively control crabgrass or broadleaf weeds when applied to bare soil prior to seeding. However, Tenacity is a poor preemergent herbicide when applied to turfed soil. Tenacity also provides effective postemergent control of crabgrass with one or two applications, as well as control of a number of broadleaf weeds.
Effects of Square One following seeding.
PHOTO COURTESY OF FMC CORPORATION.
Another new product that can be considered is the combination of carfentrazone and quinclorac called SquareOne. Designed for newly seeded turf, including interseeding and overseeding, SquareOne features the capacity to hold back weed competition until the new turf is established. The product mixes easily in water for use in sprayers and/or tank mixed with starter fertilizers. A nonionic surfactant is recommended, but not required. It is labeled for crabgrass and many small broadleaf weeds, and can be used in both spring and fall turf renovation projects.
Generally, for established turf, keeping the rootzone moist through applications geared toward matching the depth of the root system is in order. Too much or too little results in poor turf. In the days following overseeding, the irrigation timing for renovated sports fields is different, because the root system is different. The guiding principle is the same – to match the depth of the root system – but the difference is that a much smaller and weaker root system is in place with a newly overseeded field. Applications are more on the “light and frequent” side of irrigation scheduling and application timing.
John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln. Bradley Jakubowski is a professor of environmental science with Doane College in Nebraska and a diagnostic consultant in the sports turf industry.