Sonoran mountain kings breed earlier in the season that other colubrids from more temperate regions, and rarely double clutch. Many breeders have had increased breeding success by supplementing the female's diet with calcium. It is interesting to note that snake species that consume lizards as a large percentage of their wild diet often show improved breeding performance with captive calcium supplementation. It is possible that a diet composed of lizards is higher in dietary calcium than a diet of domestic mice, which may account for this phenomenon. Some breeders wait until the female has had her first post-hibernation shed before introducing the male, although breeding may occur before this event if the animals are put together.
Gestation runs from five to seven weeks after copulation.
At this time, introduce an egg-laying chamber into the enclosure. The best egg-laying chamber I have found is a plastic shoebox with an entrance hole cut in the lid. Fill the chamber halfway with damp spaghnum or peat moss. Occasionally, females will lay eggs outside of the egg-laying chamber, these eggs often turn out to be infertile. The eggs will be laid ten to twenty days after the pre-egg laying shed.