Geranium – Pelargonium

Family: Geraniaceae

Genus: Pelargonium

Intro/Brief Description

Geranium or not a geranium, that is the question! Fact is, plants used for bedding and basket plants that most people call geraniums actually belong to the genus Pelargonium. For whatever reason, these plants got stuck with the common name of geranium. To make things more confusing, plants in the genus Geranium are commonly called Hardy Geraniums or Cranesbill. Botanically, both groups belong to the same family, the Geraniaceae.

This article deals with plants commonly called geraniums in the genus Pelargonium, a name taken from Greek “pelargos,” meaning “stork,” presumably because the plants have a long, slender fruit capsule that resembles a stork’s bill. There are over 200 Pelargonium species and many well-known hybrids. These plants are tender perennials that endure light frosts, but not hard freezes. Because they are not winter hardy and come to flower quickly, they are treated as annuals in most areas of the country.

The first species known to be cultivated was Pelargonium triste, a native of South Africa. It was likely brought to a botanical garden in the Netherlands before 1600 on ships that stopped at the Cape of Good Hope. In 1631, English gardener John Tradescant brought seeds from Rene Morin in Paris and introduced the plant to England. The name Pelargonium was introduced by Johannes Burman in 1738.

Examples

Most species of Pelargonium are indigenous to Southern Africa. They are extremely popular garden plants, and thousands of ornamental cultivars have been developed from about 20 of the species. The four most common varieties seen in cultivation are the zonal, regal, ivy-leaved and scented-leaved. There are also dwarf-growing, cactus-flowered, and other novelty kinds.

ZONAL varieties, P. hortorum,, commonly called Common Geraniums or Garden Geraniums, come mainly from P. zonale and P. inquinans, both South African species. They are far and away the most commonly grown. The plants are shrubby, succulent stemmed, and grow to 3 feet. In warmer climates, such as zone 10, they can grow to 4-6 feet and become woody. The leaves are round or kidney-shaped, and soft to touch with a velvety or hairy surface. The leaf edges have indistinct lobes, and most selections show a zone of deeper color just inside the leaf margin, though some are plain green. Fancy-leafed or color-leafed selections have zones, borders, or splashes of brown, gold, red, white or green in various combinations. Single or double flowers are borne in clusters, usually of solid colors. There are many selections in white and shades of pink, rose, red, orange and violet.

REGAL varieties, P. × domesticum, are also known as French geraniums, and are mainly derived from P. cucullatum and P. grandiflorum. They include the Lady Washington Geraniums, Martha Washington Geraniums, and Regal Geraniums. They grow as bushy subshrubs with 5-lobed, upswept or cup-shaped leaves. They are more rangy than the common geranium, growing to 3 feet, with an erect though somewhat spreading habit. The leaves are about 2-4 inches wide, heart shaped to kidney shaped, dark green, with crinkled margins and unequal sharp teth. Flowers are large and showy, 2 inches or more across, in rounded, loose clusters in white and many shades of pink, red, lavender, purple. They are nearly always streaked, striped or blotched with darker colors.

IVY-LEAVED, or IVY GERANIUM, varieties are mainly derived from P. peltatum. These are mostly trailing plants 2-3 feet or longer. The leaves are ivy-like, rather succulent, a glossy bright green, and 2-3 inches across with pointed lobes. There an inch-wide single or double flowers in rounded clusters of five to ten in white, pink, rose, red, and lavender. The upper petals may be blotched or striped. There are many named selections, such as “L’Elegante” which has white-edged foliage. Other selections have white or yellow veins in the leaves. “Summer Showers” strain comes in a mixture of white, pink, red, lavender and magenta.

SCENTED-LEAVED, or SCENTED GERANIUMS, are derived from a many species, such as P. graveolens. These aromatic plants are grown for their fragrance, but do bear clusters of small blossoms in white or rosy colors. The common name generally refers to the leaf scents, such as apple (P. odoratissimum), lemon (P. crispum), lime (P. nervosum), peppermint (P. tomentosum), and rose (P. capitatim, P. graveolens). All such scented kinds are more tolerant of hot, humid summers than other geranium types.

One of the better known Scented Geraniums is the “Mosquito Geranium”, or P. Citrosum. It was developed by implanting genes from the citronella plant with code for the production of oil of citronella into a scented Pelargonium species. The citronella fragrance is released when the leaves are rubbed or crushed. The "mosquito geranium" is advertised as a natural mosquito repellant, but research has not been conducted to prove the validity of this claim.

Special Features

Geraniums are attractive to hummingbirds, and are food plants for the larvae of some Lepidoptera species (butterflies and moths), including Angle Shades. All geraniums do well in pots.

Most Zonal geraniums are drought and heat tolerant. They make wonderful bedding plants, and can be used in baskets, or grown as houseplants.

Regal varieties flower in spring and early summer, so are less suited for summer bedding plants than zonal geraniums. They also tend to get a little rangy. However, they work well in a greenhouse, and some forms are used in baskets.

Ivy geraniums with their trailing habit are ideal for hanging containers, in window boxes, on banks, and as a ground cover. They can also be trained on a trellis or along wires on walls. They are not as heat tolerant as most geraniums, so are best used outside during the summer in zones 6 and above, and as winter annuals in warmer regions.

Scented geraniums make a delightful addition to the herb garden, as edgings, in front of borders, in window boxes and hanging baskets, or as houseplants. Use them in close-up situations – in pots or in the ground. Fresh leaves can be used in cooking, to flavor jelly, and in iced drinks. The leaves can also be used in soaps, potpourris, sachets, and for insect repellents. Peppermint geranium makes a good ground cover in frost-free gardens. These plants are cultivated and distilled by the perfume industry for the scent, with the rose varieties having the most commercial importance. Scented geranium oil is sometimes used to supplement or adulterate expensive rose oils.

Hardiness

These plants are tender perennials, popularly treated as annuals. In zones 7 and above, move geraniums indoors before the first frost if you wish to carry them over winter as houseplants, or take cuttings for next year.

Growth Habit

Pelargonium has a wide variety of growth habits, from the trailing ivy-geranium to the upright shrub-like zonal geraniums. In the species, flowers have two and three petal groupings, with the upper two petals often larger and more richly colored than the lower. This differentiation often disappears from the varieties. The leaves are usually alternate.

Bloom Time

Zonal, or common geraniums, bloom from early to late summer. The Regal varieties flower in spring to early summer and Ivy Geraniums will bloom through the summer. The Scented Geraniums, as noted previously, aren’t really grown for their flowers, but will bloom late spring to late summer.

Propagation

Geraniums are usually purchased as potted plants, or may be propagated by stem and tip cuttings. However, it is also possible to grow them by seed. The seed is generally expensive.

Some widely available strains of common geranium seeds include:

• Orbit series - distinct leaf zoning and broad, rounded clusters of flowers and available in red, salmon, rose, scarlet, pink, violet, appleblossom, and white;
  
• Elite - quick to reach bloom stage, compact, and needs no pinching;
  
• Black Velvet - chocolate-brown leaves with a green edging, needs 18 weeks to flower from sowing; and
  
• Horizon - orange, red, or mixed picotee blooms and among the earliest and longest blooming geraniums.

Ivy Geranium is available in a Summer Showers strain to be grown from seed, and there are some Scented Geranium seeds available.

Germination OR Cuttings

Seed should be started indoors about 10-12 weeks before set-out time. Sow about 1/16th inch deep. Germinate the seed under lights or in a greenhouse, with bottom heat of 70-75°F. Germination takes 3-21 days.

Cuttings from geraniums can be taken mid-way through the current growing season. The growth should be neither very young and soft nor hardened and woody. Cuttings for winter houseplants can be taken in early fall. In early spring cuttings can then be taken from the indoor plants to raise new plants for outdoors use. Rooted cuttings can be kept over winter with a minimum temperature of 50°F.

To take stem cuttings, choose a healthy shoot without flowers or buds. Cut stem tips 2-6” long, cutting ¼ to ½ inch below a node – a dormant growth bud that is usually visible as a small bump on the stem near the point where a leaf attaches to the stem. Gently pull off or cut away the lower leaves. Rooting can be made more certain and hastened by dipping the base of each cutting in hormone rooting powder, but it is not essential. Press the cuttings gently into a good rooting mixture, such as equal parts perlite and vermiculite, equal parts peat moss and perlite, or equal parts peat moss and sand, to just below the lowest leaf.

Cover the pot or tray with clear plastic to keep the cutting in a warm, moist atmosphere, and keep away from strong light to prevent loss of moisture through the leaf surfaces. Keep the rooting mixture moist by spraying it occasionally with a fine mist of water.

Alternatively, cuttings can be placed in a version of a Forsyth pot, made with two terra-cotta flower pots – a small one about 3” in diameter, and a larger one about 6-7” in diameter. Bulb pots work well. Plug the drainage hole in the small pot and set it inside the larger pot. Fill the space between the pots with moist rooting medium. Place the cuttings in the medium and fill the inner pot with water. As the water passes slowly through the wall of the inner pot it provides continuous, even moisture to the cuttings.

Rooting has taken place when top growth forms, usually in 3-5 weeks. Plants can then be placed in bigger pots. Pinch out the growing tips of young plants at an early stage to promote bushy growth.

Transplanting

Seedlings should be carefully transplanted into pots to allow them space to branch. Harden off and plant out when all risk of frost has passed, spacing plants about 12 inches apart in full sun.

Soil

Plant in any good, fast-draining soil. Heavy soil would benefit from the addition of several inches of peat, compost, or perlite before planting geraniums. Sandy soil is improved by the addition of organic matter.

Irrigation

Water geraniums thoroughly. Allow the soil to dry between waterings to avoid root rot, but not so dry the plants wilt. Cycles of heavy watering, then wilting, cause leaf drop and poor growth.

Sunlight

In general, geraniums do best with a lot of sun, preferably 8 hours or more to promote good bloom. Regal geraniums need some shade in the greenhouse to prevent scorching. Potted geraniums indoors should be placed in a sunny window or the brightest available light.

Care

Remove faded flowers to encourage new bloom. Geraniums in pots bloom best when somewhat pot bound. Common geraniums may stop blooming during the summer heat in warmer zones. To avoid this, give geraniums light afternoon shade, or grow heat-tolerant varieties.

Zonal geraniums may be brought inside and kept as houseplants, or left in unwatered pots in a cool window. In spring, resume watering to start new growth.

Pests

Watch for whiteflies and aphids, particularly on indoor plants. Spider mites are occasionally a pest. Caterpillars may chew holes in leaves. The tobacco budworm (Helicoverpa virescens) can be a problem, causing tattered flowers or unopened buds.

Disease

Poorly drained soils can lead to stem and root rot. Plants are susceptible to leaf spots and gray mold in cool, moist locations. Remove faded flowers and dry leaves to prevent Botrytis fungus attacks on leaves and young buds.

Additional Info

The International Herb Association designated scented geraniums as their Herb of the Year for 2006.

References

Reader’s Digest. (April 1983). Illustrated Guide to Gardening. Pleasantville, NY. The Reader’s Digest Association, Inc.

Brooklyn Botanic Garden. Bush-Brown, Louise and James (1996) America’s Garden Book. New York, NY. Macmillan.

Fell, Carolyn & Derek (1995). Step-by-Step Sun Gardening. Harrison, OH. Springhill Nurseries.

Southern Living. (1998) The Southern Living Garden Book. Birmingham, AL. Oxmoor House, Inc.

Brown, Deborah L. and Wilkins, Harold F. (Revised 1998), Outdoor-Indoor Geranium Culture [1], Accessed 2006-11

Paun, Lou, Editor (2006), Love to Know Garden [2], Accessed 2006-11