ASHS 2025 Conference

Stratified substrates may offer some advantages in containerized plant production, but their function in the propagation environment has not been extensively studied. We tested unrooted cutting root develop and plug stability with four herbaceous species [Agastache × ‘Sunrise Red Improved’, Cuphea hyssopifolia 'Maria' (Floriglory®), Gaillardia ×grandiflora 'Eclipse' (Lunar®), and Salvia ×jamensis 'Ignition Purple' (VIBE®)] in stratified propagation substrates. We used small, round pots to mimic a liner cell (top diameter 63.2 mm, depth 61.2 mm, volume 140 cm3 ). The control was a commercial propagation mix. We created top and middle-stratified treatments, using amendments of coarse perlite, fine coconut shell biochar, and parboiled rice hulls. The top-stratified treatments had 3 cm of an amendment material on top, with the control substrate underneath. The middle-stratified treatment contained the control on the top and bottom, with a 2-cm layer of amendment in the middle. We tested the species in separate experiments, with 7 replications each, in an approximately 30 day experiment. We repeated the experiments in a second cycle. At harvest, we assigned each cutting a plug integrity rating on a 0 to 5 scale: 0 = no visible roots, unstable, 1 = minimal roots, one or two roots visible, unstable, 2 = moderate roots, more than two roots but large spaces with no roots, partially unstable, 3 = acceptable roots, many roots with only small gaps, stable, 4 = optimum roots, many roots with full coverage, stable. Most of the stratified substrates had lower ratings than the control (P < 0.05). The top stratified rice hull treatment had a lower mean rating than the control for every plant in every cycle. Cuphea and Gaillardia with middle perlite stratification were not significantly different than the control in both cycles, while all top stratified mixes had significantly lower ratings than the control for Cuphea. Root growth in stratified substrates was similar to the control in the majority of cases. Cuphea cuttings had lower total root length (mm) than the control in all top stratification treatments and the middle perlite treatments in both cycles (P < 0.05). Some non-significant trends in the data repeated in both cycles, showing repeating patterns between the stratification treatments. Stratified substrates generally had lower plug integrity than the control, with few significant root growth effects.