Home About Us Our Services Publications Testing Submissions Contact Us Links

Topdressing turf

Topdressing refers to the layering of sand and soil over turf. (For farmers and nurserymen it usually refers to the application of fertilisers to a standing crop.) Topdressing of turf is used for four main reasons:

• To restore the level of a surface after play or subsidence has altered it.
• To adjust the soil texture so as to improve compaction resistance: usually to create or maintain a coarse particle size range.
• To control thatch or the organic matter content at the surface, so as to increase speed, bounce and resistance.
• To build up soil depth.

Topdressing is often combined with coring and dethatching operations in sports field maintenance and renovation.

Examples of topdressing situations

• A badly degraded council oval constructed on natural soil with poor drainage. Coring and topdressing can improve the particle size distribution in the surface soil to prevent compaction and allow for better drainage.
• A playing surface based on natural soil where earthworm and other disturbance brings fines to the surface, causing poor drainage, compaction and waterlogging. Topdressing is necessary to maintain the correct particle size distribution in the surface.
• Any kind of playing surface where play alters the surface level. Topdressing during the playing season is needed to maintain trueness of the field.
• Bowling and golf greens, where light topdressing is used mainly to control thatch and trueness every 2–3 weeks at the height of the growing season, and more intensively during renovation.

Topdressing of special purpose soils such as cricket pitches and tennis courts is not discussed here.

What to topdress with

Playing surfaces must be able to drain under all conditions. Natural soils will generally not do this, as they have a range of particle sizes, which fit together to leave little pore space. All topdressing mixtures must maintain some pore space and hence permeability when fully compacted. A narrowly graded sand will maintain 10%–30% pore space if fully compacted.

The usual topdressing materials are composed of sand alone or sand with various proportions of sandy loam, compost or both. Common mixtures used are referred to as 80/20 and 90/10 sand/soil mixes (by volume, not by weight). However, the type of sand and the type of sandy loam are critical. Any old sand mixed with any old soil will not necessarily give the right characteristics. The only way to obtain the right characteristics every time is to base your selection of materials on particle size analysis and other physical and chemical attributes.

The commonly available “sandy loams” around Sydney are really silty alluviums and must never be used for topdressing, as they compact solidly.

The best materials have already been graded (sieved through different mesh sizes to separate the size components), and therefore they cost more. But unless you know the particle size of the topdressing, you can’t know whether you’re buying a material that can ruin your turf.

Typical rates range from 2 to 5 kg/m².

Can I topdress with compost?

Over the past 5 years we have seen an increasing use of recycled organics (mainly compost) for topdressing. On the plus side, compost adds some nutrients and increases soil organic matter content, which is critical to retention of soil nutrients. Turf certainly responds to topdressing with compost. On the minus side, it cannot raise surface levels (because it breaks down) and may result in the development of a very fine organic layer at the surface that reduces drainage. Use of compost should be seen more as a method for stimulation of the turf than to improve physical attributes.

Coarse, of course

Coarser material must overlie finer material, not the other way around. Fine soil has a naturally lower permeability than coarse soil, so a layer of fine soil can trap irrigation water and prevent it from flowing into the coarse layer beneath. This can lead to a number of problems:

• Plant growth will suffer in prolonged wet weather.
• Heavily used turf will become a quagmire.
• Traffic will more easily compact the wet soil.
• Root growth will be shallow and thatching will be encouraged.

It is thus essential to establish what your existing soil is before choosing a topdressing. The golden rule is “always topdress with a material of the same or coarser texture than your soil, never with a finer textured material”.

Greens and constructed sand profiles

These installations are very expensive to construct and can be easily degraded by using the wrong topdressing material. In both of these situations the topdressing material should be the same as the existing material. Records of the materials used in the construction of the soil are vital to being able to recreate the particle size distribution.

Narrowly graded pure medium sand hasn’t enough shear strength when dry to stand up to normal use, and a small fines content as well as some coarser sand content is needed to improve water-holding capacity and shear strength. The former Australian Turfgrass Research Institute recommended up to 8% clay + silt + very fine sand (see Table 1).

Table 1. Particle size distributions specified by the Australian Turfgrass Research Institute.

Note that such particle size distributions can be expressed as “% passing” or as “% retained”, or as cumulative gradient curves.

Natural soil ovals, fairways and playing fields

In these situations, topdressing is used to enhance playability in wet weather by modifying the particle size distribution at the surface to give an incompressible layer that will drain easily after rain. It can also be used to level surfaces after disturbance or subsidence. It is often necessary also to “sand, slit and core” first, sweeping or working the sandy topdressing material down into the cores and slits.

The specifications given in Table 1 also apply to this situation.

There is also room for adding organic matter or fertiliser if you have a very poor turf needing renovation. For example, where the existing soil is very acidic, lime or dolomite could be added to the topdressing mixture.

To improve a natural-soil playing field may take 2 seasons of topdressing in several applications to build up 20–40 mm of sandy surface material, which is the desired depth for avoiding compaction.

Maintaining trueness in existing fields

Where existing high-quality fields are performing well and need to be maintained, exactly the same material as used in their construction must be used for topdressing. It is most important to keep records, or to examine profiles and have samples tested where the history is not known.

Only where existing conditions need improving should a coarser material be used for topdressing. Never use a material finer than the existing soil for topdressing.

Quality control

It is worth paying a bit more for material of guaranteed quality. Plugging up your soil with the wrong material can cost a lot more to repair than the money saved in buying the cheapest topdressing. Always ask your supplier for a physical and chemical analysis of the material, and make sure that this matches the analysis of your soil before you topdress. Try to select a supplier with ISO accreditation.

As well as a particle size analysis (showing the distribution of each size range), you need to know the pH and organic matter content. Cheaper materials can be made from recycled concrete waste, and so have a pH that is too high for your needs.

If you can’t get this information (perhaps you’ve inherited a stockpile from a former greenkeeper), you must get the material tested before you apply it. Testing can avoid problems and costs down the track.

Further reading

Adams WA, Gibbs RJ. 1994. Natural Turf for Sport and Amenity: Science and Practice, 132–135, 182–186. CAB International, Wallingford, UK.

Handreck KH, Black ND. 1994. Growing Media for Ornamental Plants and Turf, 192–206, 223–227. UNSW Press, Sydney.

Rufford (UK). Knowledgebase.

Download as a PDF