How they can heal fastest, turf types that are more golf friendly.
By Mike Jiggens
Divots are a natural occurrence in the game of golf. They are particularly abundant on par three tees, especially when a hole is short enough to warrant a wedge or nine-iron shot to the green. They are also commonly found in the fairways of par four and five holes, especially from approach distances that are reachable for most recreational golfers.
Mending divots and allowing the cavities to heal is a task shared by both golfers – who created the wounds in the first place – and maintenance staff charged with their repair and ongoing recovery.
Speaking in February at the Canadian Golf Course Management Conference in Quebec City, Dr. Aaron Patton of Purdue University shared some of the divot research he’s done in recent years and offered advice about how to speed up the healing process and to minimize the amount of damage.
Part of his research included determining how often golfers use each club in their bag during a typical round and how many divots they would ordinarily make. A survey among golfers indicated a golfer made a divot each time he hit a shot about two-thirds of the time. Usually, both soil and grass were removed during the stroke. If the club head simply swept through the turf without taking any soil, it wasn’t considered a divot. On average, golfers took 13 divots per round, according to the survey.
Not taken into account, however, was the number of additional divots made from pre-shot practice swings.
The average size of a divot was five centimetres by 10 centimetres. Patton said there wasn’t a consistent relationship between golfer handicap and divot size. Divot volume measured by golfer handicap revealed some golfers with low handicaps might take a smaller-than-average divot while those with significantly higher handicaps were apt to take the same sized divots.
“There’s no real clear relationship between divot volume and golfer handicap,” he said.
The survey was based on divots taken from Bermuda grass, but many of the findings were applicable to cool season grasses.
On an average 18-hole golf course, about half an acre of turf is removed each season from divots made.
“This was a conservative estimate because we were doing this research with Bermuda grass, and generally Bermuda grass compared to creeping bentgrass would have a much smaller divot than creeping bentgrass.”
When taking into account the differences in divot volume from one turf species to another as well as factoring in the number of practice swings made, closer to 5,000 feet of turf might be displaced in a season, Patton said.
Higher-lofted irons will make larger divots than long irons. This was measured by the results of eight golfers who took five shots apiece with each club in their bag. The size of the divot was examined in relation to the loft of the club.
Patton said this becomes a bigger problem with divots on golf courses with shorter yardages. When several holes are only 300 to 350 yards long, more wedges will be used to hit approach shots. This results in larger, more numerous divots.
The average volume of a divot is 43 cubic centimetres. Extrapolating the number with the number of divots a golf course anticipates each season, it amounts to about 18 cubic metres of sand needed to fill the cavities. The data is based on the Bermuda grass model. Divots are more easily made on creeping bentgrass tees than on Bermuda grass, Patton said.
“The bottom line is you’re going to need a lot of sand to fill those divots.”
Creeping bentgrass has stolons to promote divot recovery but offers poor divot resistance. Its ability to hold up to an iron making contact with the turf is deficient, and some of the biggest divots are made on creeping bentgrass tees.
“It’s nice for divots to fill in and grow back quickly after we take them, but if a grass species can resist that golf club going through it, we can make a smaller divot, and that’s good for us as well because that’s a smaller area we have to repair.”
Kentucky bluegrass has rhizomes that are beneficial for divot recovery and is a little more resistant to divoting than creeping bentgrass. Perennial ryegrass is a bunch type grass that prevents it from filling in from divots, but has medium divot resistance. Fine fescues have rhizomes yet are slow to grow, making recovery less than ideal. The fescues tend to resist divoting fairly well, however.
No perfect grass for divots
Patton said there is no perfect grass type that can lessen the amount of divot repairs that are needed. Some resist divoting better than others and some recover more efficiently than others, but all have their strengths and weaknesses.
Based on a show of hands from among the superintendents in his audience, Patton estimated about 40 per cent grow their tees to creeping bentgrass while Kentucky bluegrass and poa annua account for most of the remainder. Many superintendents also grow one species on some tees and a different species on others.
“I think that’s important because we know that microclimates may have shaded tee boxes where maybe one species will do a bit better than another. I think it’s important to take advantage of the characteristics of those different species.”
If a shallow divot is taken from creeping bentgrass, it will be mostly turf that has been removed and little soil, leaving sufficient stolons remaining to allow the grass to recover. The club has essentially just skimmed off the turf.
If all of the turf has been removed along with a small amount of soil and the divot is filled in with just sand, there will be a reliance on the stolons of the creeping bentgrass to fill in from the edges of the cavity. Eventually, the creeping bentgrass will continue to grow and fill in the divot on its own.
“That’s one of the nice things about creeping bentgrass. It does have that recovery mechanism from its stolon growth.”
Kentucky bluegrass resists divoting more than creeping bentgrass. Even if the golfer’s intent is to purposely take a large divot during his shot, the turf will resist divoting. If a divot is made, yet some of the rhizomes that can regrow the wound are left behind, recovery will occur.
Not much research has been done in the area of variety selection for tees, Patton admitted.
“Is it helpful to pick certain varieties over others when it comes to recovery?”
In general, most creeping bentgrass varieties recover from divots at about the same pace and rate. Based on the limited research that has been conducted, once bentgrass has been established, there is no discernable difference among the varieties that would suggest one is better for divot recovery.
Studies have been done among different varieties of perennial ryegrass, including bunch-type grasses and those with some spreading ability. Patton said improvements are being made on some varieties of ryegrass to spread through “pseudo stolons” to fill in divot areas.
“Certainly if you have a ryegrass tee box, you wouldn’t rely solely on the grass itself to fill in the divots. You need some seed in that mixture to get your tees recovered in an adequate time.”
Although no one in the audience admitted to growing tees to fine fescues, they don’t have to be mowed or fertilized as often, Patton said. Some fine fescues have rhizomes while others are bunch types. He said the belief that planting spreading types of fine fescues might lead to divots filling in quicker isn’t true. Research shows they fill in, but it’s not from rhizomes. Rather, the wounds fill in from their edges. Because it’s a slow growing grass, the process takes longer. Research shows that even after 12 months of regrowth, no divot was completely filled in.
“If you’re considering using fine fescues, that would be something you need to take into consideration.”
Patton said most of the divot research that has been done involves cool season grasses, but the studies have been tailored more to soccer and football fields and not as much to golf.
A divot made in a grass species that easily wounds and has poor resistance to divoting takes more work to grow back in than a species that is more resistant. Rough bluegrass fares a little better than creeping bentgrass, Patton said, but both, as well as poa annua, will result in a large divot. Typically, poa annua divots disintegrate while creeping bentgrass divots can be replaced as its stolons help to keep them in place.
Golfers are encouraged to replace their divots while playing, and it’s a philosophy that should be promoted, he said.
“When we replace that divot, it may eventually die because there aren’t much roots attached to it, but it can still be helpful in filling that low space so that the next golfer will maybe have a better lie.”
Patton added that if a creeping bentgrass divot is peeled back, most likely it is helping to keep the stolons underneath and along the edges moist to promote better recovery.
Replacing divots versus filling them in
Data from a study conducted by a superintendent compared replacing divots versus filling in the cavities using a mixture of sand and seed. Twenty divots were replaced while another 20 were filled with sand and seed. In the case of the replaced divots, some dried out a little or were scalped a bit during mowing. Timed photographs showed that after one week, there was no difference between the two sets of divots. But after two weeks, the divots that had been replaced were starting to root and recover while the filled in cavities showed no apparent progress.
“I think it’s good for us to train our golfers to repair the divot by putting it back in its place if it’s possible versus just always wanting to put sand in it.”
Several golf courses have divot mix dispensers available on carts or next to tees for golfers to use when divots are created. Patton said that when divots can’t be replaced, golfers should be taught the proper way to fill in cavities with divot mix. Often a golfer overfills the cavity, not understanding the idea is to keep the repaired area level with the tee box. Frequently, however, the task of filling in divots is left to the grounds maintenance staff.
“In that case, they’re typically going out with their utility carts filled with sand and shovels and doing their best to fill in.”
About 20 per cent of Patton’s audience indicated they filled their divots with just sand. The majority used a mixture of soil, sand and/or compost. Most of the courses that allow golfers the tools to fill in their own divots don’t provide seed in the mixture, allowing only the maintenance staff to work with seed.
Patton alluded to two studies aimed at filling divots in the best possible way. One was conducted in Illinois with the other in Ontario. Both studies looked at 100 per cent sand treatment, 100 per cent compost treatment, 100 per cent soil treatment and different ratios.
In the Illinois study, trials included an 80-20 sand-compost mix, an 80-20 sand-soil mix and an 80-10-10 sand-compost-soil mix. The Ontario study factored in peat with a 50-40-10 sand-peat-clay mix trial, an 80-20 sand-compost and an 80-20 sand-peat or sand-soil mix trial. Seed was eventually added in different volume amounts in the Illinois study at one-half per cent (one scoop of seed with 199 scoops of mix), one per cent, 2.5 per cent, five per cent, 10 per cent and 15 per cent. Patton said he didn’t recall the ratio used in the Ontario study, simply noting separate studies were conducted with and without seed.
A five per cent seed volume was found to be the ideal amount among a 95 per cent sand-soil mix in the Illinois study.
“Basically, the fall was the only time of year that had a huge benefit from adding seed, but most of the time there was a benefit.”
In trials using 100 per cent sand, it was found more seed was required because there wasn’t sufficient moisture-holding capacity. An 8-1-1 sand-soil-compost mix offered the best divot recovery. Patton cautioned that if compost is to be considered in the mix that it be screened first, depending on the quality of its source. Results were the same for both Kentucky bluegrass and creeping bentgrass using the 8-1-1 mix.
The Ontario study suggested that adding seed was the most important factor for increasing recovery and was a more important consideration than the type of soil mix that was deemed best. It was found that adding compost to the mix was the second most important factor due to not only the enhanced moisture-holding capacity, but that the darker-coloured mixture might help to trap heat and encourage germination.
Patton questioned whether brown or green sand was better at promoting quicker divot recovery, adding no formal studies have been done to produce an answer. He speculated, however, that a darker colour would be advantageous in the spring and fall to warm the soil and help the turf grow faster. Depending on summer temperatures, the darker colour might prove detrimental by placing excessive heat stress onto the seedlings in the mix.
Tees boxes should be fertilized with about 25 per cent more nitrogen than fairways, he said, noting they are subject to more traffic and have more divots taken out, especially when practice swings are taken into account.
“So I think we need a little more fertility on our tee boxes than our fairways.”
An exception, he said, are tees that are subject to lengthy periods of shade because fertilizer will hinder their performance. Not as much photosynthesis takes place in shade, and the plant doesn’t require the same nutrition it does in full sun.
“Should we keep the area dry so the divots are smaller? Or should we keep them wet so that the grass recovers quicker from divots?”
Patton said trials have shown divots recover about the same whether a tee is wet or dry. Preserving water might therefore be the direction to lean toward and will keep divot sizes down.
He added research suggests plant growth regulators don’t affect divot recovery, neither slowing it down nor speeding it up.
Rectangular or square-shaped tees are more conducive to reducing compaction as compared to round or oval-shaped tees because a cleanup lap on the latter while mowing promotes compaction.
“The bigger the tee, the fewer issues we’re going to have, although sometimes it’s hard to train your crew on how to mow square tee boxes without messing things up.”
Patton said there is a tendency to mow tees too short, suggesting they are cut somewhere between the height of fairways and greens or at least the same height as fairways.
“If we mow a little taller, that plant is going to have more leaf area, will do more photosynthesis, and will have more energy to grow and fill those divots back in.”
He cautioned to keep weeds in mind when fixing divots. If using herbicides, products that inhibit the growth of seed should be considered. He suggested labels be read carefully to learn how herbicides might inhibit the establishment of grasses.