Geraniums have been popular garden perennials for a long time, and have lots of devotees. Consequently, there are lots of good sources of information on the internet. A good start is provided by the Open Directory Project's geranium category. For a primer on erodiums, this page from the UK gives a good overview.
Stimulus control is the phenomenon of a stimulus increasing the probability of a behavior (operant response) because of a history of that behavior being differentially reinforced in the presence of the stimulus.
Inhibitory control can be defined as a range of mechanisms that allow the suppression of previously activated cognitions and inappropriate actions and resistance to interference from irrelevant stimuli (Bjorklund & Harnishfegar, 1995).