The 2010 ASHS Annual Conference

Woody floral shrubs are commonly harvested for their colorful stems or flowers.  This renewal-type of  pruning often gives erratic re-growth which may  or may not yield market quality stems.  Two experiments, irrigated and non-irrigated were designed to test different pruning and restraint methods to encourage higher quality stem production.  Red twig dogwood (Cornus sericea cv Coloradensis), flame willow (Salix x ‘Flame’) and French pussy willow (Salix caprea) were included in each experiments. The experiments were conducted as randomized complete block design with at least 3 blocks for each species in each experiment. Blocking criterion was spatial proximity. One plant was the experimental unit, and treatments were randomized to all experimental units within a block. Treatments were: Control (C) - harvest pruning only. Restraint and peripheral pruning (R) - harvest plus a 24” tall section of black plastic pipe 30” in diameter was placed over/around each plant and stems that touched or protruded beyond the restraint were pruned away. The restraint was left in place throughout the growing season. Peripheral pruning (P) - same as R except the restraint was removed following pruning. Peripheral and interior pruning (I) - same as P plus stems were also pruned back and dead wood removed from an area approximately 9” by 5” in the center of the plant.  Data collected included total number of stems per bundle, number of stems with physical damage or poor color, field height of tallest stem, and field weight of harvested bundle.  Market quality stems were measured for length, diameter and number of branches plus number, location and stage of catkin development (pussy willow only).   Statistical analyses were conducted using a mixed models analysis of variance (ANOVA) implemented using SAS PROC GLIMMIX.  Significant differences among treatments were identified through the use of pair-wise comparisons. The height of pruned pussy willow, flame willow and red twig dogwood stems were not different from the control in either experiment.  However, for specific variables, individual plant by treatment interactions occurred.  For example, interior pruning of pussy willow yielded longer saleable quality stems. Field weight and number of stems were affected with the restraint treatment producing fewer stems, but often more of saleable quality. For flame willow, distance to the first branch was longer for the restraint treatment which may be a market advantage. Given the hundreds of stems harvested, the number of market quality stems was much lower than anticipated.