Physostegia purpurea Blake is a native, herbaceous perennial that has potential as a field-grown cut flower. Physostegia stems were harvested with one third of the florets open and were recut underwater in the laboratory. Fresh cut flowers treated with silver thiosulfate (STS) and held in a 2% preservative solution lasted 14 days, while control stems in deionized water (DI) lasted 6 days. Cut stems placed in darkness at 0C for 1 week had 8 days of vase life after removal from storage and treatment with STS and preservative, while stems held in DI after storage lasted only 4 days. Stems held dry at 22.5C and 43% RH for 8 hours before being placed in preservative had similar vase life as flowers placed in preservative immediately after harvest.
The capacity of plant materials to resume normal growth after exposure to low temperature is the ultimate criterion of cold hardiness. We therefore determined the low-temperature tolerance of five commercially important herbaceous perennial species. Container-grown blanket flower (Gaillardia ×grandiflora Van Houtte. `Goblin'), false dragonhead [Physoste- gia virginiana (L.) Benth. `Summer Snow'], perennial salvia (Salvia ×superba Stapf. `Stratford Blue'), painted daisy (Tanacetum coccineum Willd. `Robinson's Mix'), and creeping veronica (Veronica repens Loisel.) were subjected to 0, -2, 4, -6, -8, -10, -12, -14, -16, and -18C in a programmable freezer. The percentage of survival of most species was adequate when exposed to -10C. Producers of container-grown perennials are advised to provide winter protection measures that prohibit root medium temperatures from falling below -10C.
delayed flowering of common yarrow ( Achillea millefolium ‘Weser River Sandstone’), purple coneflower ( Echinacea purpurea ‘Bravado’), bee balm ( Monarda didyma ‘Blue Stocking’), and false dragonhead ( Physostegia virginiana ‘Summer Snow’) by 2 d