ASTM D5539-94(2003) PDF

1.1 This specification covers the material characteristics, physical requirements, and sampling appropriate to the designation of a soil or soil-like material for seed starting purposes. This would consist of the duration of germination ending after the cotyledon stage (at the opening of the first true leaves).

1.2 Seed starter mix may include natural soils and artificial mixtures of natural or artificial materials used for the initial germination of seeds to the cotyledon stage.