Auxin Application Method Affects Rooting of Herbaceous Perennials

The rooting performance of five taxa of herbaceous perennials was studied: Agastache 'Purple Haze’, Gaura lindheimeri 'Siskiyou Pink', Lavandula x intermedia 'Provence', Leucanthemum x superbum 'Snowcap', and Salvia nemorosa 'May Night'. Water-soluble salts (20%) of indole-3-butyric acid (IBA) at 1500 mg·L^-1  were applied to unrooted cuttings with one of four methods: control (no hormone), basal dip, foliar dip (to imitiate foliar spray), or immersion.  Measurements of each cutting were taken 14 days after sticking (DAS) and 21 DAS.  After visual ratings were made on a scale of 1 (no roots) to 5 (ready to transplant), roots of all crops were washed and scanned using the WinRHIZO imaging system to determine the root surface area and root volume. Dry weight of roots and shoots was also measured. Rooting was highly variable among taxa and treatments; some showed little difference between control and IBA treatments (Gaura, Leucanthemum).  If there was a response to IBA, there was either no difference among application methods (Lavandula) or the immersion application resulted in optimum rooting (Agastache, Salvia).