Propagation of Thuja x ‘Green Giant’ by Stem Cuttings: Effects of Growth Stage, Type of Cutting, and IBA Treatment

Abstract

Stem cuttings of Thuja L. x ‘Green Giant’ (‘Green Giant’ arborvitae), consisting of 22 cm (8.6 in) terminals (tips of first-order laterals) or 20 cm (7.8 in) laterals (side shoots removed from those portions of terminal cuttings inserted into the rooting medium), were collected on three dates associated with specific stock plant growth stages (softwood, semi-hardwood, and hardwood) and treated with indolebutyric acid (IBA) in 50% isopropanol ranging from 0 to 9000 ppm (0.9%). Regardless of cutting type or auxin treatment, cuttings rooted in high percentages at each growth stage. Overall rooting for softwood, semi-hardwood, and hardwood, cuttings was 85%, 86%, and 96%, respectively. Semi-hardwood cuttings were the only cuttings in which percent rooting was affected by IBA treatment or cutting type, with lateral cuttings rooting in higher percentages than terminal cuttings (92% vs. 79%, respectively), while IBA concentrations of 3000 (0.3%) or 6000 ppm (0.6%) proved optimal for both cutting types. Mean root number and mean root length varied by growth stage, cutting type, and IBA concentration. In general, rooting percentages and root length were optimized at the hardwood stage with either cutting type treated with 3000, 6000 or 9000 ppm (0.3%, 0.6% or 0.9%) IBA, resulting in >10 roots per cutting.