Vegetative Propagation of Perennial Cut Flower Flax (Linum spp.) in a Controlled Environment

Perennial flax ( Linum austriacum, Linum perenne , L. austriacum ) has a wide range of uses for the horticultural and agronomic markets. Protocols for vegetative propagation culture and production scheduling of perennial flax are needed to advance development of potential ornamental or specialty cut flower (CF) cultivars, specifically for the floriculture market. The purpose of this research was to establish vegetative propagation practices for perennial flax CF selections. Fifteen CF genotypes were tested in four experiments between week 8 of 2022 and week 37 of 2023, using 5-cm cuttings from greenhouse (GH) or field cuttings. We tested mist house (MH) rooting time (2 or 3 weeks) and rooting hormone concentrations [1000 or 2000 ppm indole-3-butyric acid (IBA)]. Experiments tested rooting time over 3 or 4 total weeks, which included 2 or 3 weeks under mist, respectively, and 1 week in GH culture before rating. Rooting success was rated using a six-point Likert scale to gauge number and length of roots per cutting. Expt. 1 rooted for 3 weeks using 1000 ppm IBA, resulting in 66.5% rooting. Expt. 2 (4 weeks, 1000 ppm IBA) had 96.4% rooting. Experiment 3 (4 weeks, 2000 ppm IBA) had 82.0% rooting. Expt. 4 (replicate of Expt. 2 but rated using a binary rooted vs. unrooted rating scale, as done in a commercial setting), resulted in 85.4% rooting. Overall, Expts. 2 and 4 resulted in the greatest mean success rates, despite the differences in root rating methods. An increased IBA concentration is not recommended for Linum genotypes, as it decreased rooting success in this study. Perennial flax vegetative propagation may be successful using 1000 ppm IBA for 4 weeks to multiply GH stock plants and produce plugs (liners) for shipping and CF production. Additional research will be needed to define the timing and cultural requirements for successful shipping of vernalized, finished (rooted, robust growth) plugs for perennial CF flax cultivars.