Influence of stratification, light, and planting depth on rabbitbrush seed germination and emergence

Rubber rabbitbrush (Ericameria nauseosa (Pall. ex Pursh) G.L. Nesom & Baird) [Asteraceae]) has potential for use as an effective element of water-conserving landscapes. To enhance availability of this species, it is important to optimize nursery seedling production. Our objectives were to determine the influence of 1) stratification (cold-moist); 2) light exposure; and 3) planting depth on germination and emergence of seeds collected from diverse populations of rubber rabbitbrush. Seeds representing a range of environments were collected from Idaho and Utah and were cleaned, sorted, and exposed to germination-enhancing treatments. Following stratification, seeds of 3 of 4 rabbitbrush populations responded with a statistically significant increase in germination percentage. More significant, stratification increased the germination rate, reducing time to culmination from 4 or more wk to 1 wk or less. Compared with seeds germinated in the dark, exposure to sunlight increased germination percentage 1.5- to 3-fold, depending on population. Any amount of seed burial markedly decreased seedling emergence for all 4 populations. Six wk after planting, removal of all but a few mm of soilless substrate resulted in emergence of a portion of the buried seeds, indicating induction and release of conditional dormancy (possibly quiescence) due to a lack of light or other factors. Responses to stratification, light, and seed burial varied by population, thus confirming previously described variability that exists among rubber rabbitbrush populations. Results of this study will help nursery growers provide optimal conditions for producing nursery stock of rubber rabbitbrush.