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.
In simple terms, inhibitory control is the process of altering one's learned behavioral responses in a way that makes it easier to complete a particular goal. Inhibitory control is a key component of cognitive control; inhibitory control is impaired in both addiction and attention deficit hyperactivity disorder. In healthy adults and ADHD individuals, inhibitory control improves over the short term with therapeutic doses of methylphenidate or amphetamine.