A common perception is that turf grass is a high water user. But is this true? Generally not, unless referring to heavily managed species that are not naturally suited to Queensland.
Slight shifts in turf grass selection and modest changes in management systems produce a result for every drop of water applied. Most warm-season turf grasses experience some browning due to water stress, but quickly recover when rain falls.
In a landmark study, University of Florida researchers carefully documented water use in a buffalo grass (Stenotaphrum secundatum) lawn and an adjacent native (to the United States) mixed species landscape, under similar environmental conditions to those encountered in South East Queensland.
Test landscapes, each measuring 5 x 10 metres, were replicated eight times to provide rigorous scientific measurements.
- Year 1: When both the lawn and the landscape species were establishing, the yearly irrigation requirement (in addition to rainfall) for lawn was 964 mm per year, 83 mm more than the adjacent landscape.
- Year 2: The irrigation requirement for the lawn (233 mm per year) was still 129 mm higher that for the adjacent shrubs.
- Year 3: By the third year there was no difference between the two.
- Year 4: The landscape plants were using significantly more water (254 mm per year) than the adjacent turf (109 mm per year).
Changing water requirements
So what do the results show? After the initial establishment year, the irrigation requirements for the landscape shrubs continued to rise from 104 mm per year in the second year to 254 mm per year in the fourth year.
Plant water use measured as evapotranspiration also rose. This was attributed to the ongoing growth of the leaf canopy with time. The water requirement continued to rise as the leaf area increased.
In addition, at the rates of irrigation applied, some of the species in the mixed planting developed stress symptoms, indicating that the irrigation needs were not yet met. In a mixed planting, for all plants to look good, the water applied has to meet the needs of the plant using the most water.
Lower lawn water use
In contrast, after the initial establishment phase, the water needs of the mown lawn stabilised. The evapotranspiration level was only higher than the adjacent landscape in the first year, when the landscape canopy was quite small. In the second, third and fourth years, the evapotranspiration figures for the lawn was lower than or equal to that of the adjacent landscape. The buffalo grass lawn was able to survive with low levels of irrigation once established.
The results suggest that lawn has a place as a low water use landscape element, in time outperforming even plantings native to an area.
Park, DM and Cisar, JL 2005, ‘Documenting water use from contrasting urban landscapes – turf vs. ornamentals’, TPI Turf News, May/June: 38-42.