A comprehensive review of planting approaches used to establish willow for environmental applications

Willow is considered an ideal plant species for environmental applications, including phytoremediation. Improving planting efficiency and reducing the costs of phytoremediation have become key steps for increasing its application. This paper reports the most update-to-date information on frequently used techniques for establishing willow, including plant material, planting methods, and the factors influencing the early establishment of trees in the field. The five main types of planting materials (rods, cuttings, billets, micro-cuttings and single-bud short branches), and the seven main planting techniques, especially different vertical and horizontal planting directions, were assessed. Factors affecting willow establishment were also reviewed, including the characteristics of planting materials (i.e., clones, cutting phenology, propagules size, pre-treatments), operation during planting (i.e., timing, orientation and planting depth) and post-planting management (i.e., soil conditions and weed management). New planting approaches with small-sized cuttings (of about 5 cm in length) have been recently proposed showing promising economical and effectiveness characteristics, especially for the establishment of willows in harsh soil and challenging conditions.