2018 ASHS Annual Conference

Three species of trees, Vitex agnus-castus L. (an unnamed white flowering clone), Acer rubrum L. var. drummondii (Hook. & Arn. ex Nutt.) Sarg. ‘Maroon’, and Taxodium distichum (L.) Rich. (test clone TX8DD38) were propagated clonally in a sequential manner over two growing seasons and transplanted to consecutively larger containers to obtain five different containers sizes of each species conforming to ANSI A300 specifications. Trees from the five container sizes, 3.5, 11.7, 23.3, 97.8, or 175.0 L (#1, #3, #7, #25, or #45, respectively), were transplanted to a sandy clay loam soil in adjacent plots for each of the three species. Each species and container size combination were placed on independent irrigation systems and soil moisture tensions were monitored to time irrigation to avoid systematically over or under-irrigating the different species and size trees. Height, trunk diameter, and canopy spread were measured at transplant and then at the end of each growing season in the field for the next five years. After just two growing seasons in the field trees from the four larger containers of V. agnus-castus did not differ statistically (P < 0.05) in height, with only the trees from the 3.5 L containers lagging behind. By the third year no differences in height were found among trees from all five container sizes of V. agnus-castus. Acer rubrum trees did not differ in height among the various container sizes by the end of the fourth growing season. For slower growing T. distichum trees no differences existed among the heights of the three largest container sizes by the end of the fifth growing season and the T. distichum trees from the two smaller size containers lagged only slightly behind. For trunk diameter, no differences were present among trees from the various container sizes by the end of the fifth growing season for V. agnus-castus and A. rubrum, and only the trees from 3.5 L containers had statistically smaller trunk diameters than those from larger containers for T. distichum. No differences in canopy spread were present in V. agnus-castus by the end of the second growing season, A. rubrum by the end of the fourth growing season, and T. distichum by the end of the fifth growing season. If one is willing to forego the immediate aesthetic impacts, ecosystem services, and greater ability to withstand mechanical damage of larger-size container stock, similar longer-term sizes in the landscape can be achieved by transplanting less expensive, more easily handed, smaller container-size trees.