Seed Size Does Not Affect Germination or Vigor of Echinacea angustifolia

Echinacea angustifolia is widely used for its medicinal properties and included in some of the most popular herbal products on the market. The seeds, however, can be challenging to germinate and have been the subject of several studies.  Previous research and personal observation suggested that seed size might influence germination. In the fall of 2013 and early spring of 2014, studies were conducted to determine the effect of seed size and seed source on germination and seedling vigor of Echinacea angustifolia. Seeds from two commercial seed companies and one private commercial herb farm that saves their own seed were used for comparison. The seeds were separated into three sizes (small=1.18mm or less, medium=2.00mm, large=2.36mm or greater) using standard sieves and sown into a commercial soilless media in 288 cell transplant flats.  The experimental design was a split plot with seed source as the main plot and seed size as the subplot, with six replications. Data were collected weekly on germination, average plant height, and average number of leaves. Two germination studies were conducted in petri dishes for approximately two weeks each under a 16-hr photoperiod in late summer 2013 and spring 2014 with two and four replications, respectively. Each was a two-factor completely randomized design with the same three seed sources and three seed sizes used in the seedling studies. There were 100 seeds in each dish. Data were collected approximately every other day, whereupon germination was considered successful at the emergence of the radicle from the seed coat. For both the seedling studies and the petri dish studies, the primary difference was observed between the seed sources. The private farm seed had significantly lower germination and seedling vigor compared to the commercial sources. The slight differences observed in germination based on seed size were statistically insignificant in both studies. The small differences observed in the average number of leaves and average plant height per seed size were also not found to be significant.  Therefore, according to the data collected in these studies, there is no correlation between germination or seedling vigor with seed size in Echinacea angustifolia.