The objectives of this study were to investigate the responses of several groundcovers to periodic mowing and determine which ones benefit from mowing in terms of aesthetic quality, density, height and thatch development.
Eight species were transplanted on 30 cm centers in September. Five species had become fully grown in 10 months and were mowed to either a 5 cm or 10 cm height. Four species received a second mowing at 10 cm 8 or 11 months later. The remaining three species became fully grown in 18 or 21 months and were mowed at 10 cm at that time. Visual quality scores were recorded monthly, as were average overall plant and thatch heights. Lantana, Osteospermum and Verbena expressed little or no long-term loss in visual quality, while their height and thatch growth were controlled well when mowed in the spring-summer period. Height and thatch growth were controlled well in Drosanthemum and Aptenia, but visual quality was unacceptable. Spring mowing appears to produce reductions in height and thatch with no significant loss in quality of Myoporum and Baccharis but with significant loss in quality of Rosemarinus.
Non-turf ground-covers occupy a significant portion of the landscape, and understanding their water requirements is important when water conservationism being practiced. Six groundcover species (Baccharis pilularis `Twin Peaks', Drosanthemum hispidum, Vinca major Gazania hybrid, Potentilla tabernaemontani and Hedera helix `Needlepoint') representing a range of observed water needs were evaluated under different levels of irrigation based on percentages of real-time reference evapotranspiration.
Treatments of 100%, 75%, 50% and 25% of ETO were applied during 1989 while treatments of 50%, 40%, 30% and 20% of ETO were applied during 1990. Plant performance ratings in the first year indicated that 50% of ETO was the minimum treatment which resulted in acceptable plan aesthetics for all species except for Drosanthemum which performed equally well at each treatment. Significant differences in performance did occur among and within species at the different treatments. Results from 1990 will reveal which species might maintain aesthetic appearance at irrigation levels between 50% and 20% of ETO. These results will be presented and discussed in terms of their significance to species selection and total landscape irrigation management.
The performance of six landscape groundcover species was evaluated when irrigated at 30% of ET0 at irrigation schedules of three times per week, once per week, once every 2 weeks, and once every 4 weeks. Potentilla tabernaemontani could not be sustained under any of the treatments. For the other species (Baccharis pilularis, Drosanthemum hispidum, Vinca major, Osteospermum fruticosum, and Hedera helix) there were no season-long differences in a species' performance or density due to irrigation frequency, but there were significant differences among species across irrigation treatments. Drosanthemum and Osteospermum provided good overall appearance and density consistently through the season. Baccharis maintained acceptable performance most of the irrigation season, while Vinca and Hedera became unacceptable in appearance in mid-season. Soil moisture content differed among species, but was not consistently different between irrigation treatments.
A previous field study had shown that Baccharispilularis, `Twin Peaks', Drosanthemum hispidum, Vinca major, Gazania hybrid, Potentillatabernaemontanii and Hederahelix, `Needlepoint', express no loss in relative aesthetic appearance when irrigated for one season at 50% of reference evapotranspiration (ETo), but three species did not perform acceptably at 25% of ETo. In this study these six species were grown in the field for 16 months under treatments of 50%, 40%, 30% and 20% of real-time ETo to more closely determine their minimum irrigation needs.
Analysis of seasonal plant performance ratings indicates that for Vinca, Gazania and Potentilla there is no significant increase in relative performance when irrigated at more than 30% of ETo. Baccharis, Drosanthemum and Hedera exhibited no significant improvement in performance when irrigated above 20% of ETo. A general decline in aesthetic appearance and performance was observed during the study in Gazania and Potentilla at all treatments, suggesting that their long-term minimum irrigation need may be more than 50% of ETo.