Submitted to: Proceedings of Northeastern Weed Science Society
Publication Type: Proceedings
Publication Acceptance Date: 10/19/2007
Publication Date: 1/1/2008
Citation: Altland, J.E. 2008. Competition from black cottonwood in nursery containers. Proceedings of Northeastern Weed Science Society. 62:47.
Technical Abstract: Cottonwood species (Populus spp.) are weedy in container nursery production throughout much of the U.S. Cottonwood species vary throughout the country, with black cottonwood (Populus trichocarpa Torr. & Gray) predominating Oregon and other parts of the Pacific Northwest U.S. Cottonwood release seed in early summer. After landing in a suitable environment, cottonwood seed germinate in 8 to 24 hours. Cottonwood can grow 6 to 8 ft in a single season with sufficient resources. The objective of this research was to document competition from one or more black cottonwood seedlings on growth of two common nursery shrubs. On May 15, 2006, hydrangea (Hydrangea macrophylla (Thunb.) Ser. ssp. serrata (Thunb.) Makino 'Nikko Blue') and holly (Ilex xmeserveae S. Y. Hu 'Blue Girl') were potted into #1 containers filled with a standard nursery potting mix. Containers were placed on a wagon and moved beneath a mature black cottonwood tree in order to collect falling seed. The wagon was moved daily to the nursery production site and irrigated, then returned beneath the tree. On June 5, containers were moved to the nursery production site and remained there throughout the remainder of the experiment. The number of seedlings in each container was thinned to 0, 1, 3, or 5 seedlings, with three single plant replications per treatment and shrub species. On August 8, containers were irrigated thoroughly to saturation. Containers were weighed just after saturation, and then again 3, 6, and 24 hours after saturation. Percent water loss from the time of saturation was calculated. On September 21, cottonwood and shrubs were harvested for shoot dry weight. Data were analyzed with repeated measures analysis of variance and means were separated with Tukey's honest significant difference test. Water loss in holly and hydrangea was affected by an interaction between cottonwood seedling number and time, indicating different water loss response over time depending on the number of seedlings present. Among both species, water loss increased linearly with increasing number of cottonwood seedlings. By 24 hours, water loss in hydrangea and holly growing among five cottonwood seedlings was almost three times as much as those growing without cottonwood. By the conclusion of the study, SDW of poplar was similar regardless of whether 1, 3, or 5 seedlings were allowed to grow. This suggests that the #1 container (2.7 L) limited poplar growth such that one seedling grew equally large as five seedlings. Among holly, only 5 cottonwood seedlings reduced SDW compared to containers with no seedlings; however, contrast analyses revealed that SDW of holly was less with 1, 3, or 5 seedlings compared to containers with no seedlings (p = 0.0683). Hydrangea SDW was reduced with 1, 3, and 5 seedlings. These data demonstrate the competitive effects of cottonwood on water availability and ultimate growth of containerized nursery crops, especially those growing in small (#1 containers) with limited soil volume.