Comparisons of Auxin Application Methods and Rates on Rooting of Perennial Cuttings

While the quick-dip of individual cuttings is the most common method of applying rooting hormone (auxin), foliar spray and immersion of cuttings has been reported as potential time- and labor-saving alternatives.  Starting with unrooted cuttings of four perennial species (Coreopsis x ‘Full Moon’, Eupatorium maculatum ‘Phantom’, Euphorbia x martinii ‘Ascot Rainbow’, and Phlox divaricata ‘Blue Moon’), indole-3- butyric acid (IBA) in the form of Hortus IBA Water Soluble Salts (20%) was applied as a basal dip, foliar spray, and an immersion solution at three rates (500, 1000, 1500 mg·L^-1) plus controls. Rooting response [rooting percentage, root dry weight (DW), and a visual root rating on a scale of 1 (no roots) to 5 (ready for transplant)] was measured at two intervals. For Coreopsis, neither application method nor rate affected rooting percentage (100%), DW, or rating by three weeks after treatment (WAT).  One hundred percent of Phlox cuttings also rooted by 3 WAT regardless of application method; root DW at 4 WAT was greatest across all application methods with 1500 mg·L^-1 IBA. Eupatorium proved more difficult to root; by 4 WAT, rooting percentage varied from 50% to 92%, with the immersion method yielding the greatest root DW and rating; immersion and 1500 mg·L^-1 IBA achieved the greatest rooting percentage. There was little difference between the dip and spray results. Spray and immersion application methods resulted in greater rooting percentages for Euphorbia at 21 DAT; by 28 DAT, there was 100% rooting with all application methods and rate combinations excluding control and dip at 500 mg·L^-1 IBA.  Root rating and mass were greatest with the spray application; spray combined with the higher rates resulted in greater root DW for Euphorbia.