Pelargonium x hortorum
Common Geranium, Zonal Geranium
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 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 Pelargonium x domesticum, Lady Washington pelargonium; Pelargoniuim x hortorum, common geranium (this group also includes variegated forms usually referred to as fancy-leafed or color-leafed geraniums); and Pelargonium 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 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).
Succulent stemmed; reaches 1 to 2 ft. high and wide as an annual. In mild climates where geraniums grow as perennials, older plants become woody and can top 3 ft. Round or kidney-shaped leaves are velvety, hairy, and aromatic, with edges indistinctly lobed and scalloped. Most varieties show a zone of deeper color that looks like a thick halo around the center of the leaf, though some have plain green foliage. Single or double flowers are flatter and smaller than those of P. x domesticum, but clusters bear many more blossoms. Varieties are sold in white and shades of pink, rose, red, orange, lavender blue, and violet. Flowers may be solid colored, bicolored, speckled, or splashed with contrasting colors.
These plants are uniform, well branched, heat resistant, and available in many colors. Because they cost more than seed-grown geraniums, they're more often purchased for containers than for bedding out.
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