There are 2 main types of annual geraniums that we grow, trailing types and upright types. I will keep this brief and concentrate on the main problems in the care of upright geraniums (trailing geraniums care is here).
I read an article years ago (that I cannot find) stating geraniums were mainly found around bogs and as it rained uphill from the bog the runoff toward the bog/pond would water the roots. The plants adapted to grow with this regular watering as its way of surviving, just as other plants evolved to survive in desert conditions with very little rainfall. So we advise our customers to water geraniums daily in ground beds and patio pots. Doing so results in extremely large multiple flower heads. If customers tell me that their blossoms are never as large as when they purchased them from us, it is largely due to incorrect watering practices, letting the plants dry too far.. More frequent and thorough watering will result in large blossoms. Please irrigate your geraniums with a “open” hose around the base, no spray nozzles!!