Production Method and Humic Acid Application Affect Hardening-Off Process and Landscape Performance of Platycladus Orientalis in Arid Climate

The scarcity of information regarding suitable conditions for tree transplanting in arid climates is a major cause for failure of most transplanting projects. This study investigated the effect of different transplant methods and biostimulant application on survival and growth of multi-purpose species oriental thuja (Platycladus orientalis). In the first experiment, trees were harvested bare-root (BR) or balled and burlapped (B&B) and hardened-off in containers for one year prior to transplanting. In the second experiment, post-transplant performance of hardened-off trees in containers (referred to as CG tress) were compared to freshly dug BR and B&B trees. In both experiments, half of the trees were treated with 300 mg/L of humic acid (HA). In contrast to the B&B trees, the BR trees did not successfully tolerate the hardening-off process. During the first year following transplanting to the landscape, CG trees showed 100% survival and achieved significant increases in all measured parameters compared to B&B and BR trees. By the end of the second year, however, the significant advantage of CG trees over B&B tress vanished, and the growth rates of trees of both methods were equaled to non-transplanted trees, suggesting that final performance for hardened-off CG trees and conventionally B&B-transplanted trees may be similar. HA application only affected BR trees, so that HA-treated BR trees had greater survival and growth indices than their control counterparts. In general, in an arid climate, the landscape manager would obtain the most cost-effective and reliable transplanting method by planting B&B thujas with no necessity for a hardening-off period and incorporation of stimulants.