Lawn can be considered a form of horticultural flooring. This green carpet, like the coverings we lay within our homes, is subject to wear by a variety of sources, such as foot traffic, cars, pets and equipment. Both human and animal behaviour follows patterns resulting in tracks or patches through the lawn. Common examples are motorbike tracks near the letterbox, a path from the back door to the clothes line, or a bare area where the dog runs up and down the front fence line. Lawn subject to breaking, turning and standing fares the worst.
Traffic: the problem
What we see in lawns is ´traffic stress´ – a combination of deteriorating turf quality (including browning and thinning) and reduced growth, accompanied by an increased percentage of bare ground.
At a plant level the lawn is being crushed, torn, scuffed, abraded and dug out. Some grasses are known to have the ability to resist wear due to attributes such as their mechanical strength at a cellular level, high shoot density and/or strongly rooted mat of dense stolons. The chemical analysis of various grasses has shown that grasses, such as zoysias with higher levels of fibre and lignin, have an improved ability to resist applied forces.
Direct damage is worst on sandy soils where tearing and abrasion can be caused by the movement of sharp particles. Coarse topdressings can sometimes inadvertently exacerbate the problem.
A further impact of traffic on lawns is to increase compaction in the trafficked area, which in turn reduces turf grass growth. In particular, wear can increase in wet weather on higher clay content soils.
Unfortunately, simply planting a species with tougher or denser shoots and stems will not solve the problem of traffic stress in lawns. Whilst some species have a tolerance to damage, there is a second factor involved as turf grass can repair itself. Some species are readily damaged, but grow so vigorously that they recover rapidly. Others such as the zoysia, whilst being resistant to damage, can take some time to recover.
Observed wear = damage – recovery.
On all soil types, sand through to clay, water deficits will reduce recovery rates and increase the percentage of bare ground during periods of water shortage and drought. Compaction on higher clay content soils can reduce the growth rate of an otherwise vigorous species.
Observed wear varies with any factor which impacts on the growth rate of the turf grass. These include seasonal changes in rainfall and temperature, the age of the turf, planting sod quality, soil physical and chemical factors and stresses such as waterlogging, pests and diseases. A well watered lawn with a very high rate of nitrogen fertilisation can develop softer leaves and not wear as well as the same lawn when it is moderately fertilized.
Agri-Science Queensland, part of the Department of Employment, Economic Development and Innovation (DEEDI), has been looking at the observed wear of turf grasses under stimulated wear testing in separate experiments in both sun and shade (see Table 1). The extent of damage varies with the intensity of the treatment, the type of damage, the species (and in some cases cultivar used within the species), and the how the turf is managed.
Table 1: The relative resistance to wear (crushing, abrasion, scuffing and tearing) of various warm-season turf grasses in two separate trials (full sun and 50% shade), along with the relative rates of recovery from wear in full sun and shade, when not subjected to other growth limitations (such as water or nutrient shortage)
|Green couch (Cynodon dactylon)||Moderate to good1||Very good||Poor|
|Soft leaf buffalo (Stenotaphrum secundatum)||Moderate2 to poor||Not tested in full sun||Good|
|Kikuyu (Pennisetum clandestinum)||Poor||Moderate||Very poor|
|Blue couch (Digitaria didactyla)||Poor||Moderate to good3||Not tested in 50% shade|
|Sweet smother (Dactyloctenium australe)||Poor||Not tested in full sun||Moderate to good|
1 Individual cultivars vary widely in their resistance to wear
2 Minor differences occur between individual new generation cultivars, however one very old cultivar wore poorly
3 Named cultivars perform better than common blue couch.
Results from trials in full sun indicate that green couch (Cynodon dactylon) cultivars performed better under stimulated wear testing than kikuyu (Pennisetum clandestinum) ´Whittet´, which in turn was better than blue couch (Digitaria didactyla) cultivars ´Aussiblue´ and ´Tropika´. Cultivar differences existed within the green couches tested, with Oz TuffTM, and ´Grand Prix´ and the hybrid couch (Cynodon tranvaalensis x C. dactylon) TifSportTM being the most wear tolerant in 2009 tests.
Wear trials in 50% shade were undertaken as part of an evaluation of soft leaf buffalo (Stenotaphrum secundatum) cultivars. In particular, newer cultivars of buffalo grass such as ´King´s Pride´, ´Sir Walter´, ´Sir James´, ´Matilda´, ´Jabiru´ and ´Shademaster´ performed well in simulated wear testing. All of the newer cultivars of buffalo grass tested out-performed kikuyu, sweet smother and green couch in the shade. Sweet smother is known for its high level of shade tolerance; however these results confirm why it is not recommended for high traffic areas. Green couch requires high light levels to flourish, so the results in 50% shade, where it would be under stress and thinning, are to be expected.
Without careful management, soft leaf buffalo grasses can develop luxuriant growth in full sun. They are not recommended for heavy traffic areas as they need time to recover from damage by growing new runners.
The differing performance of green couch in full sun experiments, compared with the shade experiment, highlights the importance of choosing the right species for all the conditions of the site.
- select species vigorous in the conditions afforded by your site
- fork to loosen soil and improve soil aeration in the worn areas
- provide adequate water when possible, fertilise and monitor for pests and diseases
- divert people, animals and machinery to other areas (including roping off) to encourage lawn recovery
- avoid topdressings with sharp particles
- manage to minimise thatch and luxuriant soft growth.
Sometimes, it seems that no turf grass will work. For example, if you have a shaded area which is heavily trafficked, the solution might be to direct where people step with pavers and use a broadleaved ground cover such as Dichondra repens, Viola banksii or Viola hederacea to fill the remaining space. However, these are not particularly wear tolerant. Zoysia matrella is the most shade tolerant of the available turf grasses, handling heavy dappled tree shade (about 20% of full sunlight) and also very resistant to wear.