Annuals, Evergreen, Perennials
The common name “geranium” is widely used for Pelargonium—but botanically speaking, it is not really accurate. To the botanist, pelargoniums are woody-based perennials (most of them are native to South Africa) that endure light frosts but not hard freezes, and have slightly asymmetrical flowers in clusters. True geraniums, on the other hand, are annuals and perennials native mainly to the Northern Hemisphere, bearing symmetrical flowers either singly or in clusters.
In the past, the commonly grown pelargoniums were P. x domesticum, Lady Washington pelargonium; P. x hortorum, common geranium (this group also includes variegated forms usually referred to as fancy-leafed or color-leafed geraniums); and P. peltatum, ivy geranium. Today, other kinds are increasingly available, including many with scented leaves.
Plants perform best in areas with warm, dry days and cool nights. They can be grown outdoors year-round where winters are very mild; in these areas, they bloom throughout warm weather. Elsewhere, they are summer annuals or houseplants. In cold-winter climates, move plants indoors before the first frost or take cuttings for next year.
Plant in any good, fast-draining soil. Amend poor alkaline soil with plenty of organic matter. Geraniums growing in good garden soil need little fertilizer; those in light sandy soil should receive two or three feedings during active growth. Remove faded flowers regularly to encourage new bloom. Pinch growing tips of young, small plants to force side branches. All geraniums do well in pots; they bloom best when they are somewhat potbound. Common pests include aphids, whiteflies, and spider mites. Geranium (tobacco) budworm may be a problem in some areas; affected flowers look tattered or fail to open at all. Prevent or limit infestation by spraying plants with Bacillus thuringiensis (Bt).
Ivy geraniums are perennials in mild climates, and annuals anywhere. They grow to 1–1 1/2 ft. tall and trail (or hang) to 3–5 ft. wide. Rather succulent, glossy, bright green, 2–3-in.-wide leaves have pointed lobes and look something like those of ivy (Hedera). Inch-wide single or double flowers in rounded clusters of five to ten; colors include white, pink, rose, red, and lavender. Upper petals may be blotched or striped.
There are many named varieties. Use ivy geranium in hanging containers, window boxes, or raised beds; it also makes a good bank or groundcover (but not for erosion control). Because it does especially well with cool nights and bright days, ivy geranium is favored along the coast and in mountain gardens.
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