Turf establishment methods
|Photo Courtesy of the Super Bowl Grounds Crew.|
|Rolls of new sod should fit tightly against each other. Have a crew on hand to ensure this tight positioningwhen the sod is put in place.|
Once you’ve determined the type of turf for your natural grass sports field, the next question is which method of establishment will best fit your program. Whether the project is new field construction, full-field renovation or in-season repair of damaged areas, you’ll need to examine the pros and cons of seeding, sprigging or sodding. The decision must be based on that field and the specifics of the situation.
Determine all potential uses of the field starting from the first use through the duration of the use period. Consider all uses, from practices to walk-throughs to games for the various teams, and such additional on-field sessions as band practices or unauthorized pickup games. Factor in special events, including graduation ceremonies and concerts, and field rental to outside user groups.
Be realistic in your assessment of what type of turfgrass cover you need to support all these events and how well that turf will hold up through the use period. Then, develop your strategy to sustain the turfgrass throughout the use period or to overseed it or replace all or a portion of it in season.
Ideally, any new field construction or full-field renovation that is seeded or sprigged should have a full year to grow in and become established before use. Realistically, few programs have enough field space to accommodate all of their user groups, so fields are pushed into play with much less grow-in time.
The minimum establishment period from seeding to field use generally is four to six months for cool-season grasses and two to four months for warm-season grasses. For sprigging, the minimum is about two months. Sod establishment for all grass types varies from the immediate use of thick-cut, big-roll sod to a minimum of four to six weeks for standard-cut sod. All of these estimates consider that the period will occur during optimum growing conditions for the grass species used. If weather conditions are less than ideal, the establishment period will be longer.
The decision is an economic one in a lot of ways, notes Mark Lucas, sports turf manager for the University of California-Davis. With 55 acres of multiple fields for intramural and NCAA varsity sports programs and a mix of cool-season and warm-season grasses to manage, he uses a combination of seeding, sprigging and sodding. Lucas says, “Consider all the alternatives. Factor in the costs of installation as well as the costs of seed, sprigs or sod. Determine the additional funds needed for the irrigation, fertilization and additional maintenance required during the establishment and grow-in periods. Weigh the overall costs as compared to field use needs to select the best fit.”
For new or existing fields, consider the soil profile, irrigation availability, staffing levels, equipment availability and the anticipated weather conditions during the windows of opportunity for on-field work. Assess the microclimates across the field and how sun or shade, heat or cold and wind movement would affect turfgrass grow-in and establishment.
For existing fields, anticipate the wear areas and explore opportunities to alleviate that wear, then determine what corrective measures will be needed, from turf augmentation through overseeding, to small area or total field renovation through seeding, sprigging or sodding.
Whatever the method, the field surface should be prepared and string-line or laser graded to the predetermined parameters, which would include any degree and direction of slope designated for surface drainage.
Seeding is an option for cool-season grasses commonly used on sports fields: bluegrasses, ryegrasses and turf-type tall fescues; for common bermudagrass and its cultivars; and for some cultivars of seashore paspalum. The paspalums and most of the seeded bermudas are used as a monostand, one cultivar only, though they often are overseeded with ryegrasses. Cool-season grasses are often seeded as polystands, either as blends (multiple cultivars of one species) or as mixtures (cultivars of two or more species). Some of the seeded bermudas are offered as multiple-cultivar blends.
Good seed-to-soil contact is essential to successful seeding. Broadcast seeding spreads the seed across the soil surface. It can be used in conjunction with aeration to create holes or slices within the soil profile that the seed can slip into. Topdressing and dragging in the cores following core aeration increase the degree of seed-to-soil contact. In-season broadcast seeding prior to practices or games allows players to “spike” the seed into soil contact with their cleats. Slit seeding or drill seeding places the seed within the soil. Hydroseeding mixes seed, fertilizer, mulch, soil conditioner and a tackifier with water, forming a slurry that is sprayed over the area to be seeded.
Seeding is an option that can cut initial costs, according to Pat O’Donnell, owner of Odeys, a field installation and maintenance company based in Omaha, Neb. “The initial costs of seeding could run about a third of sodding in our cool-season turf area, but the irrigation, erosion and weed control issues to contend with throughout the germination and longer grow-in period add to the costs.”
He notes that many facilities hope to use an early fall-seeded field the following spring; or a spring-seeded field in the fall, which is pushing the window for play-ready establishment even when conditions are ideal. Even with overseeding during the playing period, many of these fields will need reseeding within six months to a year, adding to the overall costs.
Seeding is primarily a supplemental practice for Lucas. He says, “We overseed with perennial ryegrass in the fall as a cover with the bermuda. We transition it out on our high-end fields in the spring, but do allow it to coexist year-round on some of the intramural fields with common or improved bermuda. We do use some turf-type tall fescue in landscape areas adjacent to the fields and around our new synthetic turf football field and do seed those areas. High temperatures restrict any of our seeding to the fall.”
Sprigging is an option for bermudagrasses and paspalums. A sprig consists of stolons with attached roots and rhizomes. Typically, 1 square yard of sod produces one bushel of sprigs. The heavier the planting rate, the faster turf cover is established. Sprigs should be put down as soon after harvest as possible, ideally within 12 to 24 hours for mechanical installation, to prevent drying out or heating during transport. Hydrosprigging (also called hydrostolonizing) applies the same principles as hydroseeding. Sprigging is more costly than seeding, but is the least expensive option for warm-season varieties that can’t be established by seed.
Paul Greenwell, grounds maintenance coordinator for Gwinnett County Public Schools in Lawrenceville, Ga., oversees a rapidly growing school district in the warm-season turf zone. With over 80 athletic fields now in the program, including those at the 16 current high schools, time and budget are constant considerations. Greenwell says, “We use both Tifway 419 and T-10 (now named Patriot) hybrid bermudas, selected for their aggressiveness and wear-resistance.
“In new field construction and major renovation, our preparations include laser grading. I prefer mechanical sprigging to sodding in these situations as the best way to retain that precision grade. Typically, we can achieve playable cover within 60 days here. We’re sodding a few new fields because we have only 45 days from the end of construction to the start of the playing season.”
Lucas uses sodding for establishment and major renovation of most of the high-end fields at UC-Davis, but opted for hydrosprigging in a couple of situations when there wasn’t enough budget for sod. He says, “The initial costs were greater than for mechanical sprigging, but considerably less than sodding. We had a very tight window for the soccer field. Preparation started at the end of May with the irrigation work and surface preparation wrapped for hydrosprigging of TifSport bermuda in early June. Cool, rainy weather slowed establishment, allowing weeds to become more of an issue. We did hit playable conditions in 60 days.”
Lucas says that if he used the procedure again, he’d apply a bermuda-compatible preemergence control prior to the application. He says, “The combination of weed pressure and slower establishment due to unexpectedly cool conditions put greater pressure on that soccer field. It didn’t bounce back from overseeding as well as I’d have liked, so we ended up sodding some of the higher traffic sections of it during the second year of use.”
Improvements in sod harvesting equipment and advancements in post-harvest handling techniques bring greater variety to the sodding options. Depending on the harvesting equipment used, the traditional width of the roll of sod can be expanded to 48 inches or more and lengths to 100 feet or more.
The thickness of the sod refers to the depth of the soil cut from the field. That measurement does not include the turf top growth or thatch layer. Some sod producers offer “washed” sod, washing the majority of the soil from the sod after harvest. Some offer “soil-less” sod, usually grown on a plastic base. Some offer thick-cut sod, with the depth ranging up to 2 inches. The thinner the soil layer, the faster the rooting. The thicker the soil layer, the greater the stability will be.
For long-term establishment with little layering between the soil attached to the sod and the soil profile of the field, thin-cut sod is preferred. If grow-in time is sufficient, and the budget allows for it, washed or soil-less sod could be a better choice. For short-term use, when the entire field or sections of the field are sodded just prior to a game, the thick cut is preferred in the longest continuous roll the sod producer’s equipment can handle. Whatever the thickness of the cut, uniformity of depth is essential.
When only sections of the field will be sodded, with the majority of the field surface undisturbed, the depth of cut should match the depth of the soil profile material removed when the existing damaged turf is stripped away, with an allowance for compression if the new sod will be rolled after it is placed. The result should be a smooth, level surface when the replacement sod is installed so there is no upward or downward transition between the established turf and the new sod.
Refrigerated trucks for transport give more leeway in the time available from harvest to installation. With standard delivery, the sod should be installed within 24 hours of harvest. Proper placement, with no seams between the rolls and no gaps between existing turf and the new sod, provides a playable surface more quickly and better long-term results.
Sodding has the highest up-front cost, but the shortest establishment period. Obviously, the costs of thick-cut sod will be greater than thin cut, because a greater percentage of the grower’s field soil profile is being removed. The transportation charges will also be higher due to the weight of the rolls and fewer square feet per load. Washed sod and soil-less sod will also be more expensive per square foot than standard-cut sod because of the extra steps involved in production.
The author is a contributing editor for SportsField Management.