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This research evaluated the effectiveness of biodegradable mulches for weed control in container-grown ‘Martin’ giant arborvitae (Thuja plicata) and measured the effects of these mulches on evaporation and substrate temperature. The experiment was carried out in the 2008 and 2009 growing seasons. Four biodegradable mulching materials were tested and compared with a chemical control (oxadiazon) and a non-mulched/non-treated control. Two levels of overhead irrigation were evaluated: 1) daily irrigation to container capacity (well watered) and 2) daily irrigation to 30% of container capacity (water stressed). Two weed management regimes were used: 1) hand weeding three times during the growing season and 2) no weeding until the end of the growing season. Plants were potted in 3-L containers and arranged in a split–split plot design in an experimental nursery. Ornamental shoot dry weight was measured at the end of the growing season. Weed shoot dry weight per container was recorded after each hand weeding. Water content per pot (as a percentage of water-holding capacity) was measured by weighing containers every 2 hours during the day. Substrate temperature was measured in the warmest period of the day. Mulches limited weed growth to the same extent as the chemical control. In 2008, mulched plants resulted in a higher shoot dry weight than non-treated and non-mulched plants, while in the second year, no differences were observed. The black color of the 3-L containers was probably the main factor driving substrate temperature increase, indicating mulching materials did not affect substrate temperatures. In both experiments, container water content was unaffected by mulching materials. Results seem to demonstrate that transpiration is the main component of water loss from container-grown giant arborvitae plants.

Shrubs are often used for side slope greening and protection in the urban landscape. Only a few species are commonly used in the European city environment, bestowing upon cities a monotonous appearance. The aim of this 3-year trial, set up at Fondazione Minoprio (Vertemate con Minoprio; Como, Italy), was to evaluate the performance of 25 shrub species grown on a slope during three seasons (2007–09). Moreover, to evaluate the influence of weeds on plant growth and the weeding time, two mulches (biodegradable textile and polypropylene fabric) were used in comparison with bare soil (control). Shrubs were planted in late Spring 2007. To simulate urban conditions, no pruning or disease control were applied. Irrigation was carried out only in the driest periods of the first summer. Plant height and percent cover were measured every 2 months, whereas plant phenology and state of health were recorded weekly. Chlorophyll fluorescence and chlorophyll content were evaluated on two different drought-tolerant species during the third growing season. At the end of the trial shoot biomass was measured and root characteristics (root density and specific root length) were determined. Weeds were removed twice in the first and third years and three times in the second year. Time for weed removal was recorded for each experimental plot. Results show that the highest growth (height and biomass) was detected in mulched plots, probably because of both limited weed competition for water and nutrients and lower water loss by evaporation. Plants grown in bare soil showed higher root density and finer roots compared with mulched plants; this may be explained by the necessity of the plant root system to explore the soil to reach for water. Differences in growth, groundcovering, and root characteristics were observed among species. As a result of higher mulching cost and the poorer root characteristics of mulched plants, bare soil and fast growing shrubs should be used to limit weed competition and assure a satisfactory slope greening and consolidation.