Crotalus viridis mate between March and May. They have internal fertilization; males have a hemipenis which they use for copulation. Females give birth to between 4-21 live young in late summer or early fall. The babies are able to take care of themselves immediately and require no parental care. They are from 22-28 cm long when born and are already venomous. They reach sexual maturity after three years. Males may compete for females during mating season; however, body size of males does not seem to be a trait that contributes to mating success. In areas where females are scarce, males spend more time searching for females, and are not generally observed fighting over females.
(Duvall, 1997; Fitch, 1998; Melli, 1999; Reptiles and Amphibians of North Dakota, 1999; Crotalus viridis viridis, 1999)