While there are a number of options for seeding and overseeding grass, it's tough to beat slit seeders for their overall effectiveness at achieving a consistently high level of seed-to-soil contact for successful germination. And while a slit seeder alone is no guarantee of success — proper watering, fertilization and mowing are also equally important — modern slit seeders are well-respected among landscape professionals for the quality results they can deliver.
SLIT SEEDERS 101
There are slit seeders available for primary seeding, or seeding into bare dirt, but overseeding — seeding over established turf — is the most common type of slit seeding operation for most landscape professionals. As such, slit seeders for overseeding will be the primary focus for this article.
Slit seeders utilize closely-spaced vertical cutting blades or discs to create a shallow furrow, or slit in the turf, in which seeds are placed. The seed is stored in a hopper until it's delivered to the soil and, depending on the machine, a roller or series of packer wheels may follow behind the seed head to close the slit around the seed to promote additional seed-to-soil contact.
The delivery system is responsible for effectively delivering the seed to the slit. Some machines place seed directly into the slit, which is preferable to systems that essentially broadcast seed over the slits and hope they go in. A delivery system that places seed directly into the slit will require less seed to achieve success.
With the ability to easily maneuver around landscaping and tight areas common in residences, walk-behind slit seeders are most often used by landscape contractors. These units are powered by a small engine, and typically have a seeding width of 20- to 24-inches. The verticutting blades have a secondary dethatching effect as well, and most walk-behind units can function well as a dethatcher simply by leaving seed out of the hopper.
The larger, more open spaces of a sports field or golf course require larger, most often tractor-mounted, PTO-driven overseeders. These units typically seed a 48- to 60-inch swath, allowing them to cover a lot of ground quickly, but their maneuverability in tight spaces is limited. Many of these larger units will utilize verticutting or disc-type blades.
SLIT SEEDER APPLICATIONS
Though the concept of creating a parallel slit and placing seed into that slit is similar, there are significant differences in the design and performance parameters of a slit seeder used by sports turf or golf crews, when compared to seeders typically employed by landscape contractors.
Overseeding is often performed by landscape contractors to replace turf that has died due to weather or disease, or to re-invigorate the lawn. Contractors will often perform aeration prior to overseeding with a slit seeder, which provides additional opportunities for seed-to-soil contact.
The natural dethatching effect of the verticutting blades leaves a protective layer of thatch above the slits to protect the seed and hold moisture in during seed germination. An added bonus is that walk-behind slit seeders often function well as a dethatcher by simply running the machine without seed in the hopper. For turf with an excessive heavy thatch layer, it may be helpful to run the machine in a dethatching function (dispose of the excess thatch) prior to overseeding. This opens up the turf and allows for more seed-to-soil contact.
For golf and sports turf managers, who often use overseeding as a turf maintenance practice to address overuse or stress (in addition to its seasonal use in response to weather or disease-related die-off), it is not necessarily desirable to combine verticutting and dethatching functions into the overseeding operation. In fact, for these applications, it's often preferable to have as little disruption to existing turf as possible while still achieving the necessary seed-to-soil contact, considering that the turf needs to rebound to a playable, green and beautiful condition quickly following overseeding.
As a result, the blade design on tractor-mounted slit seeders is different than what is found on walk-behind models. Most tractor-mounted seeders utilize a series of disc-type blades. While some designs have non-powered disc blades rotating in a forward direction (at the same pace as the seeder), other designs feature powered counter-rotating blades. Historically, non-powered blades caused less disruption to existing turf, while powered blades provided a better quality slit, but that paradigm is quickly shifting.
Recent advances in blade design have reduced the damage caused by powered blades to existing turf while still creating the optimum clean slits for which they are renowned.
Seed spacing is also an important factor, as closely spaced blades reduce the number of seeding passes necessary to achieve seeding success. Look for a machine with closer seed spacing — a seeder with 1.5-inch spacing will give twice the seed density of a machine with 3-inch spacing.
Remember to consider what type of surface you'll be seeding. While a traditional tractor-mounted slit seeder can handle a flat surface, it's limited on undulating, or uneven terrain. Because the seeder is typically one, 48- to 60-inch wide seeder head, its ability to react to high or low spots in the turf surface is limited.
New seeder designs have introduced independent floating seeder heads to tractor-mounted overseeders, which arrange multiple smaller seeder heads side-by-side on the seeder chassis. This allows independent articulation of the seeder heads over humps and into depressions that would cause inconsistent seeding with most traditional tractor-mounted slit seeders.
THINGS TO CONSIDER AT PURCHASE TIME
How you intend to use your new slit seeder will largely determine what machine type you purchase. Most landscape contractors will be best served with a walk-behind unit, while sports turf and golf course managers will inevitably gravitate towards the productivity potential of modern tractor-mounted, PTO-driven models. Be sure to choose a seeder appropriate for the application — a machine designed for seeding golf course greens would not be the right choice for seeding a sports field, for example.
You'll also want to consider the equipment you plan to use the seeder with. Specifically, check the horsepower required to operate the seeder and make sure your equipment can meet its requirements.
Once you've decided on what type of slit seeder you want to purchase, it's important to think through how you plan to use the machine, and choose equipment that easily adjusts to the types of seeding you're going to do.
The amount of time it takes to set a slit seeder up for varying seed and seeding conditions is an important consideration. Seed depth and seed flow are two adjustments that you want to have be as easy as possible to make, as they are the two most common adjustments you'll make on a regular basis. Look for a machine that offers no-tools depth and seed gate adjustments.
And as you get ready to use your new slit seeder, don't forget that the success of any seeding project, whether overseeding or primary seeding, depends on proper watering, fertilization and mowing.
Too many seeding projects fail to produce significant results because the care of the turf after seeding was left to the homeowner. Light, frequent applications of water are absolutely critical, as they keep the seedlings and soil moist to encourage germination. When combined with the application of starter fertilizer prior to seeding, frequent light waterings get the grass off to a quick, healthy start.
Timing is also an important factor that can contribute or detract from seeding success. Spring and late-summer are traditionally the two best times of year to seed or overseed, but as mentioned earlier, sports turf and golf course managers have begun to adopt overseeding as a season-long maintenance practice to address specific issues with their turf.
If you only seed one time during the year, the late-summer to early-fall time frame is the single best time to get it done because of hospitable weather and reduced competition from weeds.
THE BOTTOM LINE
Slit seeders and overseeders have become useful seeder types among turf care professionals of all persuasions — and for good reason. When combined with proper site preparation and after-seeding care, a modern slit seeder can help you achieve a high level of seeding success.
Scott Kinkead is the executive vice president of sales and marketing at Turfco Manufacturing (Minneapolis, Minn.).
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