Seed germination of hemp (Cannabis sativa L.) cultivars responds differently to the stress of salt type and concentration

•Fiber hemp and seed hemp were firstly studied on the effects of salt-alkali stress.•Fiber hemp was more adaptive to neutral salt and showed stronger salt tolerance.•Low concentration (50 mM) of neutral salt stimulated seed germination.•The growth of radical and hypocotyl was more salt-sensitive than seed germination.•Both hemp cultivars were more sensitive to alkaline salt stress.