"Geranium" is the common name of plants that belong to two different genera comprised of more than 600 species. The range of light conditions is as wide as the choice of species. Some geraniums need full sun to bloom, while others require shade to grow well. Tropical or annual geraniums can tolerate direct sun. Hardy or perennial geraniums grow best in light shade.
One Name; Two Types of Plants
The name geranium refers to two distantly related but very different species of garden plants. When used as a genus, Geranium refers to a group of hardy, mostly shade-tolerant perennial plants collectively referred to as bloody cranesbill. It also refers to sun-loving potted or bedding plants that belong to the genus Pelargonium, which are called storksbill. Pelargonium, also known as zonal geranium, are not frost hardy and usually are treated as annuals, but can be brought inside to survive the winter.
The bedding or zonal geranium that belong to the genus Pelargonium flourishes in full sun. While able to tolerate morning shade, the common flowering summer geranium will not live or bloom well if planted in full shade. This sun-loving flower is well suited to well-drained, slightly dry situations; over-watering is a common cause of death. To encourage prolific, season-long blooming, remove spent flowers and stalks, a practice known as dead heading. The common garden or summer geranium, comes in a rainbow of colours from white, pink, red, to salmon, orange, violet.
The hardy geranium is a true botanical Geranium that survives winter cold and freezes, returning every spring. Sometimes known as bloody cranesbills (Geranium sanguineum), these woodland species do well in light shade. Low-growing and mostly carefree, the more direct sun this geranium receives, the more important it is to plant it in well-drained soil.
The botanical family Geraniaceae contains many species worldwide. Two of the genera (Pelargonium and Geranium) provide many well-known and useful plants for the garden. Geraniums that require full sun include scented geraniums (Pelargonium spp.), and ivy or trailing geranium (Pelargonium spp). Meadow cranesbill (Geranium pratense), wild geranium (Geranium maculatum) and showy geranium or purple geranium (Geranium x magnificum) all prefer part sun to shade.