Geraniums are one of the most popular indoor and outdoor flowering plants and with good reason! There are a wide variety of geraniums that differ in flower color, leaf shape, growth habit, and use. These versatile plants can be used as annual bedding plants, in hanging baskets, and in containers both indoors and outdoors. Annual garden geraniums are members of the genus Pelargonium. ("True" geraniums are hardy perennials which belong to the genus Geranium.) Some of the major types of Pelargonium geraniums include the following kinds.
Common Garden or Zonal Geraniums (Pelargonium x hortorum) are widely sold bedding plants. They have distinct, dark markings or bands (commonly called zones) on their leaves. Several newer, fancy-leaf varieties possess silver, white, gold, red, or purple markings in the leaf. Flowers are often large and may be single or double. Flower color includes red, pink, salmon, and white. Common garden geraniums can be grown from cuttings or seed.
Ivy-leaf Geraniums (Pelargonium peltatum) have a vine-like or trailing habit with smooth, leathery, ivy-shaped leaves. Flowers are single or double and available in the same colorful variety as the zonal geraniums. These geraniums are attractive in hanging baskets and window boxes. Ivy-leaf geraniums are not as heat tolerant as the common garden geranium.
Scented Geraniums are made up of several species of Pelargoniums. Plants have a wide range of leaf types (some are more deeply lobed than others) and colors. Leaves of scented geraniums possess lemon, rose, peppermint, nutmeg, apple and other fragrances and are excellent houseplants. Flowers on scented geraniums are not as showy as the other geranium types and are normally white, pink, or lavender.
The "mosquito geranium" is a scented-leaf-type geranium that releases the citronella fragrance when the leaves are rubbed or crushed. Since the citronella oils are released only when the plant tissue is rubbed or crushed, plants growing in containers on the patio or deck will not repel mosquitoes. The citronella oil used in candles and other commercial products is obtained from citronella grass (Cymbopogon nardus).
Geraniums for outdoor use should be planted outside after the danger of frost is past in your area. Geraniums prefer fertile, well-drained soils that are slightly acidic. The plants should receive at least six hours of sunlight daily. Plants in shady areas will bloom less and are more susceptible to disease. Regular watering is required for most geraniums. During dry periods, a deep soaking once a week is usually sufficient for bedding geraniums, while container plantings often require more frequent watering. If possible, avoid overhead watering because wet foliage encourages disease development. When unavoidable, overhead irrigation should be done in the morning hours which allows the foliage to quickly dry, reducing the potential for disease. Geraniums respond well to regular fertilization. During the growing season a dilute solution of a soluble fertilizer applied once a month should keep garden and container geraniums growing and looking healthy. There are several disease and insect pests common for geraniums. The best control for these problems is prevention by proper placement, maintenance, and early detection.
This article originally appeared in the April 23, 1999 issue, p. 48.