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.
A stimulus causes an action or response, like the ringing of your alarm clock if you didn't sleep through it. Stimulus is a word often used in biology â something that causes a reaction in an organ or cell, for example. In financial and economic contexts, a stimulus may be an incentive: the money you spend on your membership is a stimulus for hitting the gym.