Improving seed germination of native perennial Phlox longifolia

Seeds of native species of perennial phlox often germinate poorly for producers of native plants. To determine seed treatments that might improve germination, we conducted a study on the native longleaf phlox (Phlox longifolia L. [Polemoniaceae]). Seed treatments included a 7 °C (45 °F) cold treatment, a 21 °C (70 °F) warm treatment, 10 or 20 ml/l liquid smoke, 1000 or 2000 ppm KNO₃, 100 or 500 ppm GA₃, and a 21 °C distilled water control. Seeds were placed on filter paper in Petri plates and germinated in the dark. All treatments except the 7 °C stratification were incubated at 21 °C for 4 wk. At least 90% of Phlox longifolia seeds germinated during the 7 °C cold treatment within 7 to 10 d and had the highest germination percentages of all treatments. The 500 ppm GA₃ treatment induced approximately 37% of P. longifolia seeds to germinate in 4 wk, but germination in GA₃ treatments was characterized by cotyledons emerging first with few radicles emerging. The 21 °C stratification, liquid smoke, or KNO₃ seed treatments failed to induce germination. Germination percentages of P. longifolia seeds in all treatments increased sharply when seeds were moved from 21 °C and into the 7 °C refrigerator. Seeds of P. longifolia exposed to a 7 °C cold treatment germinated quickly at high percentages (> 90%), making this treatment practical for nursery propagation of this native perennial.