An age-old practice

One of the oldest cultural practices performed on golf courses is the art and science of topdressing. Not only is topdressing one of the oldest practices, it might be one of the most important. Topdressing can be defined as the application of a thin layer of material, such as soil or sand, to the surface of existing turf.

At one time, topdressing fairways seemed impossible, but now it's starting to become more commonplace.

Topdressing has evolved throughout time. Initially a practice performed only on greens, it’s now performed on greens, tees, approaches and even fairways. Years ago, one might have received a strange look from someone in the golf course business if he said, “Someday we will be topdressing fairways on a consistent basis.” The fact that this practice is being adopted for use over almost the entire golf course speaks volumes about its benefits.

But the key to topdressing can be summed up in one word: sand.

The use of sand as a component has been around for years. It has even been written that Old Tom Morris used sand for topdressing in the late 1800s to smooth and firm greens. However, it wasn’t until the early 1970s when sand started to dominate the mixture used to blend a topdressing material. In fact, it also was during this period that straight sand made major inroads as a topdressing material by itself. This immediately created much controversy. The thought of growing turfgrass on straight sand, with no soil or organic matter mixed in, was out of the question to many. Even today, the debate hasn’t subsided completely. One fact is certain, though: Straight sand is the dominant material used by most for this practice.

The major scientific benefit of topdressing is the dilution of the upper organic matter fraction of the turfgrass surface. As the grass plant grows, senescence of roots and above-ground plant parts contribute to organic matter build-up. This organic matter build-up is diluted through sand topdressing.

The key word is dilution. At one time, many thought the major benefit to topdressing was the breakdown of organic matter. This was true in the old days of the 1-1-1 mixtures but isn’t the case with the present day use of straight sand. Sand is inert basically and has no microbiology that can contribute to the decomposition of organic matter. So with topdressing, sand is used to mix with, or dilute, the organic matter at the surface and to maintain or increase sufficient pore space.

Greens
So how much should superintendents be topdressing their greens? This is possibly one of the most popular questions asked about this practice. In recent years, topdressing practices have become more of a calendar event rather than a scientific event. This shouldn’t be the case. However, with the help of research by Robert Carrow, Ph.D., of the University of Georgia, the question can be answered with scientific data.

Many superintendents use fertilizer-type spreaders to apply their light summer topdressing.

Carrow conducted extensive research about the organic dynamics in the upper surface of sand-based greens. He found that an organic matter content of greater than 4 percent by weight in the upper 2-inch surface should become a red flag for greens performance. So with this in mind, the goal of less than 4 percent organic matter becomes the all-important target as superintendents plan their aerification and topdressing strategies.

To keep the organic-matter content below the 4-percent threshold, suggestions have been made to apply sand at about 50 cubic feet per 1,000 square feet per year. This said, there are two important factors that should be used in the equation before adopting 50 cubic feet of sand per 1,000 as the all-important amount.

First is the length of the growing season. Some parts of the country have a growing season as short as three or four months, and other parts have a 12-month season. Should courses in both these areas of the country be on a 50-cubic-feet-per-1,000-square-foot rule? Probably not.

Working sand into aerification holes and the turfgrass canopy is an important task.

Secondly, and maybe the most important part of a topdressing program, is plant growth rate. Remembering the most important fundamental aspect about topdressing, applications should be in direct proportion to plant growth. Plant growth directly influences the amount of thatch development. Therefore, to dilute the organic matter with best results, topdressing volumes and frequencies should be increased as the growth rate increases. The same applies to the plant when growth decreases – topdressing volumes and frequencies should be decreased.

Another factor that should be considered is the amount of nitrogen applied in the fertility program. For example, there are two golf courses with similar conditions: golf course A applied 2 pounds of N/M per year, and golf course B applied 5 pounds of N/M per year. Should both of these courses adhere to the 50-cubic-foot rule? Probably not, because even though the suggested 50-cubic-foot amount might be a good guideline, it’s not a steadfast rule.

There also have been suggestions that applying 50 cubic feet of sand per year would dilute the organic matter sufficiently to eliminate aerification. And one researcher wouldn’t go as far as saying superintendents don’t need to aerify, but says it’s something to look at.

“There are about 15 courses in Nebraska that haven’t used core aeration on their greens in the past 10 years and are having great success with just topdressing,” says Roch Gaussoin, Ph.D., of the University of Nebraska. “This is certainly food for thought.”

Benefits
The greatest scientific benefit of topdressing might be controlling (diluting) the organic matter percentage in the upper surface, but there are others benefits. The ability of topdressing to produce a smooth, firm and faster putting surface is the biggest benefit from a playability standpoint. Let’s face it, when Old Tom Morris applied sand to a green in the late 1800s, he wasn’t thinking about the 4-percent-organic-matter guideline in the upper 2 inches.

In the current world of fast green speed, topdressing is an important factor that helps achieve speeds demanded by golfers. Research indicates frequent topdressing in the range of 2 to 3 cubic feet of sand per 1,000 square feet every two to three weeks can increase green speeds (ball roll) significantly. It also shows ball-roll increase doesn’t occur until the material settles sufficiently into the turfgrass canopy, which occurs five to seven days later.

Drawbacks
With all the benefits of topdressing, there are many mistakes that can be made with topdressing programs. First and foremost is selecting the proper sand. Matching the compatibility of the sand particle size of a growing mix (root zone) and the topdress material is the most critical decision in any program. Many greens have been destroyed by selecting sand too fine that resulted in a perched water table. So, quite possibly the most important part of a sound topdressing program is to have potential sands tested by a qualified laboratory for compatibility. Unfortunately, too many times sand selection is based on cost, which usually means the wrong sand.

Laboratory testing of sands might be the most important part of a topdressing program.

Topdressing also isn’t an easy procedure when you consider plant health. Sand is an abrasive material and can damage plant tissue, which can lead to additional plant-related problems. When a green is topdressed with sand, it’s like placing a piece of sand paper over the surface. Until the sand settles sufficiently, the plant is at risk. These risk factors increase with normal golfer traffic and various maintenance machines. The abrasiveness of sand also is magnified when the plant is under stress from adverse weather conditions. So when the calendar indicates to topdress greens, but the weather station indicates otherwise, the decision can be critical.

Fairways
At one time, topdressing fairways seemed like an almost impossible ordeal. In the current world of turfgrass management, it’s becoming more commonplace. Originally started in the Pacific Northwest, golf courses throughout the United States are adopting fairway topdressing. Looking back at James Beard’s 1982 book, “Turfgrass Science and Culture,” he indicated fairway topdressing would be too costly for what could be accomplished. Times have changed.

Heavy topdressing in conjunction with aerification is an important part of diluting thatch.

Unlike the art and science of topdressing greens, fairways are quite different. When it began in the Pacific Northwest, it was about playability. With the tremendous amount of rainfall in that region of the country, topdressing fairways was determined to be the best way to develop firmer and drier conditions. Building up a sand-cap-type layer allows for a more playable surface. This developed surface also allows for additional benefits such as: less turfgrass disease problems, improved mowability, improved drainage, and most importantly, more revenue. Many clubs in the region soon found the cost of the program could be offset by improved income.

Another benefit observed in the Northwest from sand topdressing fairways was the reduction of earthworm castings. The abrasiveness of the sand became a natural deterrent to earthworm activity. This was a big plus for clubs with earthworm problems because other control measures worked marginally.

It didn’t take long for this procedure to migrate eastward. Many clubs adopted this practice to achieve the same results. Even though these clubs weren’t located in regions with the same rainfall as the Northwest, the benefits were too good to pass up.

Throughout the past century, the art and science of topdressing has continued to evolve. This evolution has seen changes in topdressing materials, methods and areas of the golf course. As technology continues to advance in the next century, one thing is certain: The age old practice of topdressing will remain toward the top of the cultural practice list. GCN

Kevin J. Ross, CGCS, is director of golf course management at Country Club of the Rockies in Vail, Colo., and president of Ross Golf Agronomy. He can be reached at kjross@vail.net.