User blog comment:AldoHyde/The Sim's Pen - 17th January 2016/@comment-5248145-20160117050433

The Gardener family is a rather interesting family. You are right that these PlantSims don't appear to spawn their young. Whether that is because they can't or just don't know they can, it seems that PlantSimism is a genetic trait passed on that doesn't manifests itself until the teen birthday -- at least in the world of The Genesis Project. How dominant or recessive this gene is will only be seen as more generations arrive. So far it seems that it can only be passed on by the dam (the Sim giving birth), and it almost always passes that way. There is only one Sim who was birthed by a PlantSim and wasn't one himself.