Embryogenic tissue of hybrid larch (Larix× marschlinsii Coaz) was multiplied on Medium M (modified MSG medium supplemented with the plant growth regulators (PGRs) 2,4-dichlorophenoxyacetic acid (2,4-D; 9 μM) and N-6-benzyladenine (2.25 μM)). After 1 week, cultures were transferred to either MSG lacking PGRs (Medium C–) or MSG lacking PGRs but supplemented with 1% activated charcoal (Medium C+). Embryos were sampled after 1 week on Medium M, C– or C+. Embryos were analyzed by ELISA for abscisic acid (ABA), abscisic acid–glucose ester, 2,4-D, indole-3-acetic acid (IAA), indole-3-aspartate (IAAsp), zeatin (Z), zeatin riboside (ZR), isopentenyladenine (iP) and isopentenyladenosine (iPA). Transfer of embryos to Medium C+ reduced the embryo concentrations of 2,4-D and iPA, but resulted in elevated concentrations of IAA, IAAsp, ABA, Z, ZR and iP. Charcoal reduced 2,4-D concentrations of embryos by an order of magnitude greater than PGR-free medium alone. Charcoal affected embryo concentrations of five of the eight PGRs quantified. Use of either C+ or C– medium as part of the maturation protocols also affected germination and plantlet establishment of the embryos. A 1-week treatment on Medium C+ positively influenced plantlet establishment and generally reduced variability during both germination and plantlet establishment.