Growth Characteristics of Woody Plants for Irrigation Management of Container Gardens

Background and objective: This study analyzed the growth characteristics, in relation to the soil moisture content, of trees planted in an environment with limited soil depth to provide the baseline data for effective irrigation management. Methods: The experimental treatment was divided into soil moisture contents (SMC) of 20%, 15%, 10%, 5%, and 1%, and the respective watering times were set accordingly. As for plant materials, Nandina domestica, Euonymus alatus, Thuja occidentalis, Hibiscus syriacus, Pinus densiflora, and Pyracantha angustifolia, were chosen for this study, because they are highly likely to be used in urban street environments. Results: The minimum irrigation point suitable for each species was determined by considering various aspects of visual quality and water efficiency in terms of plant growth, including characteristics such as height, root diameter, rootlet development, and weight. Our results indicate that N. domestica should be watered so that the moisture content of the soil is of at least 5%, based on the balance between the stem and roots, as well as on visual quality. E. alatus and P. angustifolia are suitable for watering that results in at least 10% SMC, considering the height, root growth, weight, and visual quality of plants. As for T. occidentalis, it showcases moderate growth with a soil moisture content of at least 5%. Finally, the minimum irrigation time required to obtain 15% SMC is appropriate, in terms of plant growth, fresh weight, and visual quality, for H. syriacus and P. densiflora. Conclusion: This study suggested a basic irrigation guideline for container gardens where trees planted in environments with limited soil depth can be managed so that they are visually appropriate and in good condition of growth.