Topdressing is the process of adding a thin layer of material over the surface of turf. A variety of materials can be used in a topdressing program including sand, peat moss, soil, and compost, as well as mixtures of these mediums. While originally associated with the golf course industry, topdressing is now used on golf courses, sports turf fields (including baseball, football, and soccer fields) and lawns. Athletic turf managers use topdressing and aeration to help with field drainage and compaction problems. Many turf managers are finding that topdressing their athletic fields improves their playability. Some benefits provided by topdressing include a smoother playing surface, better turf density and color derived from uniform moisture and growth, the elimination and control of thatch, more efficient use of water resources, and an increased efficiency of fertilizers.
1. Why do I need to topdress? - There are many reasons for topdressing. You may need to smooth or level the playing surface. You may need to modify the root zone to increase water holding, adjust water percolation rate, change air circulation ability or pore space, alleviate compaction problems, adjust pH level, or a multitude of other reasons. There may be other problems that need to be dealt with like thatch, black layer, hydrophobia or others. This is just a partial list of reasons that people topdress turf areas.
2. How do I select a topdressing mix? - Two areas to examine in selecting a topdressing mix are the physical characteristics and the chemical properties. The physical characteristics of the topdressing should be similar to the area being topdressed. That means that particle size distribution should be similar. Similar size particles mean similar porosity and similar percolation rates. Using a topdressing mix that is radically different from the current root zone can result in layering problems that may cause poor drainage, limit growth through the layer, restrict air, water and nutrient movement into the root zone and may kill the turf. If you need to change the present root zone mix and decide to make the change by topdressing, the change should be gradual. A program of frequent, light applications over a period of time will allow a gradual change. But it is usually best to use a topdressing mix that is physically similar to the current rootzone mix.
The second important aspect of the topdressing mix is the chemical properties. Is the pH level acceptable? Most plants, especially turf grasses, grow best in a pH range of 6.0 to 8.0. The growth is usually limited by soils that are either too acidic or too alkaline. A single topdressing outside this range may not affect the overall pH level a great deal, but repeated applications will adjust the pH up or down far enough to affect the turf growth. What is the cation exchange capacity or ability to hold and supply nutrients? Turf grass needs many nutrients for growth and if the root zone can hold on to these nutrients for the turf rather than letting them leach out, the turf will need less fertilizer. That means less work and less expense. Does the topdressing have organic matter or other nutrients to provide for the turf growth? Plants require more than just air and water to grow. The soil can only provide part of the required nutrition and the available nutrients will vary. But all root zones need supplements. These may or may not be added as part of the topdressing. For instance, carbon, nitrogen, some minerals and humic acid are all available in various organic materials. A good organic material will provide some of the needed nutrients and also help hold nutrients and fertilizers as they are added. It is important to determine the chemical requirements of your turf and adjust your topdressing to fit these requirements.
3. Why not use straight sand? - There are many reasons to add an amendment to sand for your topdressing. The pH level of straight sand can fluctuate a great deal. Sand does not hold water or nutrients very well. Over time your playing surface will lose the ability to hold water and fertilizer. This will add up to additional costs. A straight sand root zone will allow water to run right through it and this will leach out many other nutrients. This is not only costly, it is bad for the environment. Sand is usually inert and has no microbial activity. A lack of microbial activity can result in disease problems, thatch problems or other problems. Sharp sands can damage the turf. Although this may be the cheapest method initially, long term use of straight sand as a topdressing medium can be very expensive.
4. Why do I need to add an organic material? - You can add almost every nutrient and characteristic you need to grow turf. The difference is the amount of work needed and the long term cost. Using a good quality organic material will pay for itself many times over in saved labor and wasted chemicals or water. A side benefit is keeping all those wasted chemicals out of the groundwater system.
5. Adding an organic material to sand for topdressing is time consuming, is there an easier way? -There are several easy ways to use an organic material in your topdressing. The easiest way is to buy a mix already blended from the sand company. Many sand companies around the country have started blending topdressing for their clients. The added expense for the ready-made topdressing is easily offset by the labor saved. Another easy way is to buy an organic material that mixes easily.
6. Why is microbial activity important? - It has been found that microorganisms in the soil can benefit plant growth in many ways. Some microorganisms help transform nutrients, such as nitrogen, into forms that the plants can use. Many bacteria produce hormones that stimulate plant growth. Other microorganisms help control thatch problems by assisting in degradation. It is also thought that there is a group of microorganisms that help plants defer or resist diseases. More benefits are being discovered all the time. The high microbial activity is why a product like peat is far superior to other amendments with low or no levels of microbial activity.
7. What about the danger of introducing weeds or diseases? - The danger of diseases or weed seeds being part of the organic material can vary depending on the source of the organic material. Less decomposed organic materials have a higher chance of causing problems than highly decomposed materials.
8. How do I determine the best organic material to use in my topdressing? - There has been a great deal of research done in the area of organic material and soil amendments. The actual needs of your turf will determine a great deal of what you should be looking for. Availability and price will be other key conditions.
9. How often do I need to topdress? - The frequency of topdressing will depend on the reasons for topdressing and the needs of your turf. If your fields were built with high quality materials and maintained properly, the topdressing is probably only needed for cosmetic reasons, to make sure you have a good level playing surface and maintain the current rootzone. In a case like this, 2 to 4 light topdressings throughout the season will be sufficient. If you have more serious concerns on your fields, more frequent topdressings may be needed. You may need to topdress every 3-4 weeks throughout the entire season to help rebuild problem areas. This frequency may need to be maintained for several years to replace or recreate the root zone without having to completely reconstruct the field.
10. How much topdressing do I need to use? - Like the previous question, the answer will depend on your individual circumstance. However, Sport Turf Supply, Inc. recommends using light coatings of topdressing and increasing the frequency if large amounts of topdressing need to be applied. The average sports field will probably need to use approximately 50 tons of topdressing mix for each application.
11. Should I aerate before topdressing? - Aeration is used to combat a variety of turf problems. Commonly, aeration is used if you have compaction problems and occasionally for thatch or layering problems. Topdressing after aeration will allow the new root zone material to penetrate the problem area. In time and with repeated applications, this should help relieve these problems. However, it is not necessary to aerate before every topdressing application.
12. What is thatch? - Thatch is a layer of living and dead grass stems and roots and other organic matter that is found between the soil surface and the grass blades. Thatch development signals an imbalance between the amount of organic material produced by the plant and its rate of decomposition. The growth rates and growth habits of the turf, as well as the maintenance the field receives, are major factors in thatch development. Bermuda grass is considered a heavy thatch producer.