Effect of Mulching on Plant and Weed Growth, Substrate Water Content, and Temperature in Container-grown Giant Arborvitae

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.