Geraniums are best suited to a cool greenhouse and a night temperature of 45 to 55 F. Good air circulation and a fresh atmosphere are essential. Contrary to popular belief, geraniums must be watered well. True, they do best when allowed to dry out between waterings, but mine are usually watered once a day in winter and twice a day in summer, depending on the weather. Through gray winter days, once or twice a week is sometimes enough. You have to feel the soil to know, for overwatering can be as harmful as dryness and subsequent wilting.
In winter, geraniums revel in full sun and prove it with a magnificent crop of flowers. In summer, shading is necessary to avoid burning of foliage and to prevent rapid drying out of soil, especially in small pots. Actually, there is no part of a geranium that will not make a nice new plant if propagated in sand. I have stuck inch-long pieces into the propagating bed just on a whim, and found to my delight that they developed into fine little flowering plants in a short time.
The "Handsome Dozen"
The big zonals are the best for long-time bloom here are twelve to give you enormous satisfaction. (But for fun I hope you will investigate the other fascinating groups.) 'Birds Egg', 'Blaze', 'Double New Life', 'Enchantress', 'Helen Van Pelt Wilson', 'Magnificent', 'Merry Gardens White', 'Mrs. E. G. Hill', 'Orange Richard', 'Party Dress', Apple Blossom Rosebud', 'Toyon'.