Can biochar be used as a seed coating to improve native plant germination and growth in arid conditions?

• Companies market biochar as a seed coating to improve plant germination and growth.
• This is the first study to evaluate biochar as a seed coating on four native species.
• Biochar seed coatings did not improve germination for any of the four native species.
• Seeds of two species coated with biochar showed slight improvements in growth.
• Biochar may not be effective as seed coating for establishing native plants.

Direct seeding is a common large-scale restoration practice for revegetating arid and semi-arid lands, but success can be limited by moisture and temperature. Seed coating technologies that use biochar may have the potential to overcome moisture and temperature limitations on native plant germination and growth. Biochar is a popular agronomic tool for improving soil properties, such as water availability and nutrient retention and has been recently marketed, but not tested, as a seed coating. We analyzed the effect of biochar seed coating thicknesses on the germination and growth of four plant species native to western United States: mountain brome (Bromus marginatus), prairie junegrasss (Koeleria cristata), Wyeth's buckwheat (Eriogonum heracleoides), and western yarrow (Achillea millefolium). Across different temperature and water potential treatments using environmental chambers and polyethylene glycol (PEG) solutions, biochar coating applied at different thicknesses had either a neutral or negative effect on germination for all species. In the field, biochar seed coatings slightly improved mountain brome root weight and prairie junegrass cover. Our results, alongside the high economic expense of native plant seed and direct seeding operations, suggest that biochar, by itself, may not be an appropriate seed coating for improving native plant establishment.