Sodding is frequently the most obvious choice for rapid turf establishment, but sod requires the same amount of initial care as seed or sprigs and must be given the opportunity to mature before traffic and play are introduced. Photo by Adobe Stock
Editor’s note: The following article first appeared in the July 1996 issue of GCM. Because of its timeless insights for turf managers, we’ve dusted it off and are presenting it anew.
There are five basic ways to accelerate turf establishment: increasing the seeding or sprigging rate; mulching, hydroseeding or hydrosprigging; strip or row planting of sod; solid sodding; and increasing fertilizer rate and frequency.
Each option has advantages and disadvantages over conventional grassing methods. Because all projects are on a fast track once approved, many superintendents use several or all of these options.
Soil preparation
Proper soil preparation is the most important element in establishing a rapidly growing, healthy and lasting turf cover. Whether the planting is done dry or wet, live or dormant, scattered or solid, soil preparation must be the same.
Not every site enjoys a good loam topsoil. But the topsoil should be relatively clear of rock and large organic debris; loosened to a depth of 4 to 6 inches; tested and amended with the necessary organic and mineral elements; and smoothed to a grade suitable for even distribution of the seed or plant material. Failure to do this properly will handicap any grassing attempt.
Conventional grassing
To get a better feel for the alternatives, all parties in the construction process must clearly understand conventional golf course grassing. Starting with a relatively clean, properly prepared topsoil, seed or live grass sprigs are inserted using some type of mechanical device to ensure optimum soil contact.
The number of seeds or sprigs planted per given area depends on the selected turfgrass cultivar. The grassing rate is based on the principle that adequate space provides for healthy, individual plant development with minimal competition. It also assumes an adequate grow-in and maturation period for the turf to develop the density and wear tolerance needed for play. This may be as long as two growing seasons for cool-season grasses or as short as three months with warm-season grasses.
Nutrient applications are based on maintaining a steady growth rate during turf development without fertilizer burn or loss to the environment. Following this standard protocol, the owner is assured of having a reasonably healthy turf cover at opening with minimal risk and cost.
The pros and cons of increasing turfgrass planting rates
Seeding
One of the simplest options for rapid establishment is increasing the number of planted seeds or sprigs. For example, the nominal rate for seeding Penncross bentgrass is 1½ pounds per 1,000 square feet. It seems reasonable that doubling this rate would ensure faster establishment and shorten the time between seeding a green and playing on it. Unfortunately, this doesn’t take into account increased seedling competition, which results in a turf plant more susceptible to stress and disease.
In research and field testing, significantly increasing the seeding rate of cool-season grasses under optimal growing conditions has resulted in markedly poorer uniformity in the second season. That’s when competition begins to thin the turf stand. This result is devastating to putting green quality.
One way to shorten establishment time without increased competition may be to pre-treat seeds to improve viability. University of Wisconsin research has shown that most grasses can accommodate lower seeding rates when treated with metalaxyl fungicide before shipment. This treatment gives good initial protection against Pythium and seems to enhance the viability of the individual seeds through germination and emergence.
Metalaxyl treatments allow lower-than-recommended planting rates in new stands while achieving the same turf density. Although the per-pound seed cost is significantly higher, it’s offset somewhat by the reduced planting rates. It can also significantly shorten establishment time without risking increased competition.
Sprigging
The problem with significantly increasing warm-season grass planting rates by sprigging isn’t competition — it’s the difficulty of getting uniform placement at high rates.
Most sprigging machines efficiently plant between 300 and 400 bushels per acre of fairway-type bermudagrass. For greens, the rate is usually between 18 and 25 bushels per 1,000 square feet. At these rates, it’s assumed there will be a 90- to 120-day growing period before play begins.
As the rate increases with higher sprig counts, less growth is needed to fill empty spaces. This can establish grass faster. However, doubling bermudagrass rates on fairways or greens may only marginally gain readiness for play under optimal growing conditions, and it can significantly increase the number of wasted sprigs left drying on the surface.
To maintain adequate soil-sprig contact for survival between irrigation cycles, most experts suggest two passes of the sprigging device across the target area, calibrated at the normal rate for each pass. You can also spread sprigs on one pass at the doubled rate, then cut diagonally across the target with a slicing machine. This pushes the grass plants still exposed on the surface into the soil. Even then, the limit of positive return is somewhere around 1,200 bushels per acre.
Sprigging costs increase proportionally to the sprig count and the number of machine passes. And a heavy sprigging rate in July is unlikely to yield a corresponding return in readiness for play after a 90-day grow-in period. As the optimum planting window begins to close, however, these higher rates make more sense.
When to increase rates
There is, however, a time to use increased planting rates: when the planting period is past the point of optimum turf development. With cool-season grasses across the East, Midwest and non-mountainous West, this is any seeding done after September or when soil temperatures regularly drop below 60 degrees F.
The optimum time to plant bermudagrass throughout most of the South and West ends in August, when soil temperatures drop below 70 degrees F. There would be no need to risk higher grassing rates if all projects were planted before then. Rates for the many projects that don’t plant by then can increase proportionally – up to a point — the closer you get to winter dormancy.
My standard recommendation on cool-season grasses seeded beyond the September optimum is to increase the seeding rate by 50%. If the specification rate is 2 pounds of Penncross per 1,000 square feet, I recommend 3 pounds. With bluegrass and fine fescue roughs, 200 pounds per acre becomes 300 pounds.
There are two reasons to do this. The turf will appear denser for marketing purposes. (It actually has better density for erosion control.) Also, you can expect a mortality rate of 50% or higher on young seedlings desiccated by freezing temperatures and no supplemental irrigation. The initial density increase usually evens out as the turf enters the next growing season, and additional plants protect each other during the winter.
The same principle applies in warm-season grassing, but you should gradually increase the sprigging rate as dormancy nears, culminating in a maximum of triple the normal rate.
Sprig viability
Whatever the rate, total time required for a turf cover from broadcast sprigging is directly related to the vigor of the harvested parent grasses and the care the sprigs get from harvest to planting.
It’s always good to visit the sod farm before harvesting and check out the steps taken to ensure maximum sprig viability. All harvested sprigs should contain three or more growth nodes (or crowns), have a minimal amount of green leaves present for better drought tolerance, and be
planted within 48 hours.
It’s best to harvest sprigs by digging or sod shredding instead of verticutting. This gives you the strongest rhizomes located closest to the soil surface. Sprigs with higher viability require lower planting rates to achieve rapid establishment.
Mulching turfgrass
Mulching plays an important role in the success of late-season grassing by insulating the soil surface against cold, as well as protecting the young grass plants against frost and drying.
Straw mulch is the most common. Apply it thinly enough for sunlight to reach the soil surface yet thick enough for protection and moisture retention. (The rate is usually between 2 and 3 tons per acre, depending on the thickness of the straw stems.) Make sure the straw is relatively free of noxious weeds, is applied evenly, and is either mechanically crimped or sprayed with a tacking agent to hold it in place.
Wood cellulose mulch is applied hydraulically over the recently planted area in a method similar to hydroseeding. Hydromulch provides a more uniform cover with no risk of weed contamination in the fiber and no crimping or tacking to hold it in place.
The main disadvantage to hydromulching is cost, which can be substantially higher than that of other methods, depending on the desired thickness. It takes between 1,500 and 3,000 pounds of cellulose mulch to cover an acre, along with 3,000 to 10,000 gallons of water to apply it properly. It costs between $500 and $800 per acre — a substantial investment.
If you’re planting during optimal establishment periods, consider mulch for quick establishment. Mulch provides extra moisture retention during peak drying periods and protects new seedlings from heat stress and excess radiation. It also helps stabilize the soil, preventing erosion from thunderstorms, and protects against weed competition.
Hydraulic planting of turfgrass
Golf course contractors and superintendents are increasingly turning to hydroseeding or hydrosprigging to plant turfgrass. Hydraulic planting applies seed, fertilizer and mulch at the same time, eliminating secondary mulch applications for stabilization and moisture retention. Also, presoaked seeds and sprigs are considered more viable than dry-planting methods, giving quicker establishment.
How much faster these techniques are is subject to debate. But it’s generally accepted that hydraulic planting can save up to a month in the turf development process, especially when done before or after optimal grassing periods.
Other advantages over conventional grassing include better resistance to soil erosion, easier access to difficult slopes and tight spaces, and less disruption to the finish grade. And when the mulch is dyed green, the site takes on a more finished look. All of these advantages make hydraulic planting an attractive option.
Surprisingly, the cost of hydroseeding isn’t a major factor. Conventional hydroseeding runs from $1,200 to $2,000 per acre, depending on the seed type and the total grassed area. Dry seeding by a contractor runs close to that, with bentgrass fairways costing from $1,700 to $2,000 per acre and bluegrass roughs from $1,200 to $1,500 per acre. Considering hydraulic planting’s advantages, it should be your choice when you need rapid establishment.
Photo by Nathan Jennings/Unsplash
There are, however, drawbacks and risks to consider when deciding whether hydraulic planting is right for your situation. One of the most important steps is keeping the seed on target with clean, sharp contours where grass types meet. There’s nothing worse than bentgrass scattered in bluegrass roughs, which can easily happen with misguided hydroseeding.
The problem isn’t as severe with bermudagrass hydrosprigging because tees, roughs and fairways are frequently the same grass type. Even then, corruption of a green with the more aggressive, coarse-textured Tifway can cause years of headaches for a superintendent trying to maintain a pure dwarf putting surface. Operators must take extreme care to prevent this type of cross-contamination.
Another potential disadvantage of hydraulic planting is the need for immediate irrigation of the target surface once application is complete. Irrigation deficiencies or incomplete planting from machine breakdowns can quickly dry seeds or sprigs in the exposed upper layer of the mulch fiber, causing a relatively high mortality rate.
Without direct soil contact, seed must germinate and grow toward the soil before obtaining any reserve moisture. The same principle applies for live sprigs, as roots have to grow down through the mulch layer to reach the soil. Any drying of the mulch at this critical stage can result in significant plant loss.
You can compensate for loss from surface drying by increasing the planting rate by one-third to one-half of the dry-seeding recommendation. With sprigs, the rate is somewhat limited by the amount of material that can physically pass through the pump, pipe and hose without clogging the system. Anything above 800 bushels per acre requires virtual elimination of the wood fiber mulch from the tank mixture. In either case, the ability to get water to the newly planted area determines how quickly a turf cover will develop.
Row planting of turfgrass
Row planting sprigs is another option for warm-season grasses such as hybrid bermudagrass. This procedure is used mainly to renovate existing turf. Row planting is done by a machine that plows a narrow set of furrows, usually set 6 inches apart, into which sprigs are introduced and anchored by closing the furrow. Maximum rates are between 400 and 500 bushels per acre. The limiting factor is the number of sprigs that can be placed in the furrow without spilling onto the surface.
The primary advantage of row planting in renovation is convenience. Because it causes minimal disruption to the target area, play can resume in a relatively short time and continue as the new turf develops. But there is another, less evident advantage in row planting: the greater survivability of sprigs in drought.
Because live sprigs are inserted directly into the root zone, you can use the soil’s natural moisture retention to stretch the intervals between irrigation cycles. This is a great asset for rapid establishment, especially with limited or poor-quality water.
Cost is a significant factor with row planting. According to Bill Carraway from Select Turf in Georgia, row planting currently costs between $800 and $1,000 per acre, as opposed to broadcast sprigging, which costs between $400 and $600 per acre. Consider row planting’s increased survivability and convenience when weighing its cost against its benefits.
Sodding turfgrass
Sodding is frequently the most obvious choice for rapid turf establishment, with easy-to-see advantages and almost instant results. The course is immediately marketable, and the site is stabilized against erosion. And, most importantly for a golf course, play can begin in as little as one month after completion. For cool-season grasses, this results in revenue production a full year ahead of a conventionally seeded course with a normal grow-in period.
The difference is almost as striking for zoysiagrass, with at least a six-month advantage over seeding. Also, depending on the quality of the sodding job, you can gain three months by sodding bermudagrass.
But compare those benefits with the high cost and not-so-obvious risks of sodding. The price of sod depends on the type of grass desired, the variety’s availability, and the distance from the sod farm to the golf course. In addition, a remote site will pay more per truckload than will a course in the southeastern sod belt. And, after a relatively severe winter, sod costs usually increase with demand for replacement turf.
Take these price variations into account when contemplating sodding. Generally, installed cool-season rough sod runs about $17,000 per acre. Sodded bentgrass fairways and tees cost up to four times that amount, and greens sodding often exceeds $2,000 per 1,000 square feet. Bermudagrass tees, fairways and roughs are somewhat less expensive, at $11,000 per acre. Greens are about $1,300 per 1,000 square feet.
For example, if a cool-season golf course has 10 acres of tees and greens, 30 acres of fairways, and 80 acres of roughs, the cost to sod the entire site is in excess of $2.8 million. The cost of sodding bermudagrass on the same area is a bit more reasonable, at $1.5 million. With zoysiagrass fairways and tees, the cost is a bit higher, at $2 million. This is a substantial investment in rapid establishment.
Beyond cost, sodding has more physical risks. Sod-layer interface problems are a major cause of putting green failure. Sod grown on a clay-based loam is not compatible with a sand and peat root-zone mixture. The reverse is also true of older greens containing a soil base sodded with grass grown on a sandy mix. This same principle, though frequently overlooked, applies when soil mismatches occur on sand-based tees or fairways.
Correcting the resulting infiltration problem takes several years of cultivation, and the superintendent must live with the sick turf. Elation over turning quick revenues is rapidly lost when the facility must close again and again for aerification and regrassing.
Using washed sod
To avoid a sod-soil interface problem, plant sod that has been grown on a medium that closely matches the area where you are planting it. In practice, this is next to impossible unless the sod farm is either on or very near the intended installation area. To protect against the risk of a mismatch, you can purchase washed sod. This sod has the soil removed, or washed, from the roots. Cost frequently limits this practice to greens and tees, but it’s often the procedure of choice for sodding greens built to USGA recommendations.
There’s a critical period of adjustment after installing washed sod. If not handled properly, it can cause almost immediate failure. The sod, which is frequently cut thin for production and transportation, lies dormant for some time before initiating new root growth. Also, the mat of existing root material has air instead of soil filling the open spaces between roots and crowns, creating a hydrophobic thatch cushion just above the soil. This soil-less thatch layer is then capped with surface topdressing, creating a sandwich of slowly decomposing organic material. You must vigorously core aerify the newly created layer to incorporate topdressing into the voids.
Until this occurs, a washed-sod putting green will feel somewhat soft underfoot, and you run the risk of the layer interfering with water movement from the surface into the root zone. This problem isn’t as severe as that generated by a sod-soil mismatch. It can, however, reduce initial putting quality and prove a great disappointment to an employer expecting championship conditions when the course opens.
Other risks of sodding
Sodding has other risks to consider before deciding to go to the expense. Purity and viability of the sod is every bit as important as that of seed or sprigs.
While a seed certification program has long been in place, one is only now being developed and implemented for warm-season turf. Florida has such a program. Georgia, among other states, will soon follow. In any case, there’s no substitute for visiting the fields personally and submitting samples to a qualified test laboratory for purity verification.
Pest infestation of sod isn’t always visible until after installation. Weed seeds and insect eggs are difficult to spot without careful lab examination, while juvenile weeds, worms and grubs are somewhat easier to find with a close visual field inspection. Once again, submitting samples to a qualified testing facility is the best protection against trouble.
Poorly watered sod has a weak root system, as does sod that has been under-fertilized or treated with certain chemicals. So before placing an order, carefully review the maintenance records of the sod you’re planning to purchase.
Sod that hasn’t been maintained at or near your height of cut will take longer to adjust after installation. This is more of a problem when the sod farm mows higher than required for golf play. Density will be low, and scalping will almost certainly occur for an extended period. For best results, the sod should be cut at the target height for about a month before harvesting.
Sod requires the same amount of initial care as seed or sprigs and must have an opportunity to mature before play begins. I don’t know how many sod installations I’ve seen where the sod has burned up from lack of irrigation, gone almost dormant from lack of fertilizer, or been torn up and worn away from golf cart and maintenance equipment traffic.
The very reason people turn to sod can be the biggest threat to its success. While sod makes the course look finished, it’s not. My recommendation is to wait at least four weeks after sodding to begin subjecting sod to traffic and play. During that time, treat it like the new turf that it is. The quicker sod is subjected to the stresses associated with mature turf, the greater the risk it will fail.
Turfgrass fertilization
There’s a prevailing industry perception that applying nutrients in great quantities results in faster establishment. This is true to a point, but only if the rate and frequency match the plant’s ability to take and use the applied nutrients. You waste anything more than that through leaching or runoff.
Photo by Freepik
A sensible grow-in fertilizer plan — for warm- or cool-season grasses — uses moderate rates at frequencies determined by growth rate and color. Soil testing is valuable in determining soil reserves, but these visual cues are much more accurate in the short term on new establishments. Generally, cool-season grasses establish well with 1/2 pound of nitrogen per 1,000 square feet applied weekly on greens and tees, and 3/4 to 1 pound every two weeks on fairways and roughs. For bermudagrass, the rate is 1 pound of nitrogen per week under peak growing conditions.
Balance nitrogen, phosphorous and potassium until the initial turf cover is established, and adjust it thereafter according to the soil tests. Likewise, once the turf has the desired density, reduce nitrogen rates and frequencies to help harden the turf against wear and disease.
Using these guidelines, a successful grow-in should use between 10 and 15 pounds of nitrogen for warm-season grasses, and between 8 and 12 pounds for cool-season grasses. While there are reports of courses using twice that amount, I haven’t seen the need for these higher rates.
Fertigation, or the injection of fertilizer into the irrigation system, is an excellent method of supplementing the grow-in process. Constantly feeding low rates of nutrients to the turf through foliar application causes growth and development to remain steady with little or no waste of fertilizer material. The initial investment in a good fertigation system more than pays for itself in increased fertilization efficiency.
Putting it all together
Any project uses a combination of the establishment methods discussed here. With cool- or warm-season grasses, dry seeding or broadcast sprigging without mulch is still the most widely used procedure. The closer you get to the end of the growing season, or the earlier you plant in the following year, the greater the benefit of mulch. Straw mulch is frequently applied to reduce the risk of seed, seedling and sprig loss. Seed and sprig rates are also adjusted accordingly, always accounting for the problems associated with excess density on cool-season grasses.
Hydromulching is seldom done unless there’s a problem acquiring clean straw. Hydroseeding or hydrosprigging are used wherever steep slopes or other terrain problems make mechanical dry planting difficult. In particularly dry periods, or where irrigation is restricted, hydraulic planting extends the irrigation interval. In this situation, however, initial watering is even more critical than with dry planting methods.
Row planting of warm-season grasses is the option of choice for any renovation with an existing turf stand. Sodding is usually done around greens, tees, bunker complexes and erosion-prone areas. Most projects use between 10 and 20 acres of sod, depending on the construction budget and type of terrain. Strip sodding is also used on some sites in conjunction with seeding or sprigging to help control erosion. Solid sodding of the entire course or sections of the course is a rare but valuable alternative as long as the cost is justified and precautions are taken to reduce the risk of failure.
There are many ways to establish turfgrass on a golf course. The method you choose will depend on your resources and schedule. The key to being successful is understanding all the options and selecting one or several methods that best match your goals. Make sure the pros and cons are communicated clearly, and know the limitations of having fast grass.
A former superintendent and a member of GCSAA for 21 years, Jonathon Scott, CGCS, is an agronomist for Jack Nicklaus Golf Services and lives in Grand Rapids, Mich.