University of Vermont Extension 
Department of Plant and Soil Science

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GERANIUMS OR PELARGONIUMS?

Dr. Leonard Perry, Extension Professor
University of Vermont
 
What most gardeners call geraniums—those lovely annual flowers in reds, pinks, and whites—are really pelargoniums.  This is the common name you’ll see if you visit Britain or websites from other countries, and is the scientific genus name. Our annual geraniums are tender plants, native mostly to South Africa.  The true perennial geraniums, or cranesbills, are hardy and native to North America and Europe. 

Both the annual and perennial geraniums share the same shape fruit, resembling a bird’s beak, hence cranesbill and the other names.   Geranium is from the Greek word (geranos) for crane, and pelargonium from the Greek word (pelargos) for stork.
           
Discovered in South Africa by traders rounding the Cape of Good Hope, annual geraniums quickly gained acceptance in England in the late 17th century. In 1786, Thomas Jefferson was so enamored with the geranium that he sent plants from France to horticulturist John Bartram in Philadelphia, who in turn introduced them to America.

Fascination with the tender geranium continued over the next century with several successful attempts to hybridize. Between 1820 and 1826, Robert Sweet's five-volume book on geraniums was published and became the definitive guide to this interesting plant variety.

Today, plant breeders are developing varieties for new colors, compactness, heat tolerance, disease resistance, and earlier, longer blooming time. There are approximately 250 species of geraniums with more than 10,000 different cultivars. The most popular color is red, although others are increasing in popularity. There are four basic types of annual geraniums.

Common or zonal geraniums are the most popular garden geranium, named from their "zoned" leaf markings. They have clusters (umbels) of many individual flowers held on long stems above the foliage. Colors include white, salmon, pink, orange, red, magenta, and lavender.  Flower shapes include ones with thin, spiky petals (“stellar), ones resembling tulips, long petals of the cactus-flowered, spotted and speckled, or tight rosebud shapes. 

Most zonals are 1- to 2-feet tall, although there are dwarfs less than 10 inches and miniatures less than 6 inches tall.  The fancy-leaved cultivars (cultivated varieties), many of which were developed in the Victorian era, are grown more for their yellow to red variegated leaves.

Ivy-leaf geraniums are named for the ivy-shaped foliage held on long, brittle stems, and have a trailing growth habit.  This makes them a favorite for hanging baskets and window boxes. The more open flower clusters than common geraniums vary from reds to pinks.

Regal or Martha Washington geraniums make bushy plants, and have colorful large flowers which are often bicolored with decorative stripes. They thrive best in cool, sunny locations and will bloom throughout the season where temperatures do not exceed 60 degrees (F).  Plants may stop flowering in the heat of the summer, but will resume once the weather cools in the fall. Angels are smaller versions of Regals, their flowers resembling pansies.

Scented-leaf geraniums are available in many flavors including rose, lemon, peppermint, nutmeg, coconut, chocolate, mint, and apple.  Uses include cooking or fragrant, dried pot pourri. To release the scent, rub the foliage.  These annuals, many of which are heirlooms, are good to place near a walk or border edge where their fragrance can be easily and often sampled.

Until the early 1960’s, annual geraniums were propagated “vegetatively” by cuttings.  In 1962, plant breeder Dr. Richard Craig at Pennsylvania State University developed the first seed propagated geranium—Nittany Lion Red.  Other cultivars then followed from other breeders, including hybrids of various parents. It is these pioneers of the pelargonium that we have to thank for the seeds we buy in catalogs today. More recently, many geranium plants we find for sale are once again vegetatively propagated.  Many of these are from improved series, crosses among two or more species or types of geraniums.

If growing your own geraniums from seeds, have patience as they are rather slow.  You’ll want to sow them indoors in containers 8 to 10 weeks before the last average frost date for your area.  In much of the north, this would mean sowing sometime in March.  Figure on the first flowers 3 to 4 months after sowing.  Sow slightly below the surface, keep the soil moist but not wet, and keep it warm (70 to 75 degrees) as on a seedling heating mat or other warm area.  You can use a south-facing window, or fluorescent lights on 12 to 14 hours a day.  Once a couple sets of leaves have formed, start fertilizing weekly with quarter-strength houseplant fertilizer.

Geraniums thrive in average to cool temperatures and should be planted outdoors well after the danger of frost is past. Some of the newer series such as the Caliente, Calliope, Grandiosa Regals, Candy Flowers, Fantasia, and Master Idols all have much better heat tolerance than older cultivars.

Most geranium cultivars prefer bright, sunny locations (ivy types like cooler, dappled light) with at least 4 to 6 hours of direct sun daily. Space them 8 to 12 inches apart.  Soil should be moist, well drained, slightly acidic, and high in organic matter such as peat moss or compost. Water well after planting, but don't overwater.  And water early in the day, so leaves and flowers dry before nighttime.  This will lessen the chance for disease such as gray mold.

Annual geraniums need plenty of fertilizer to grow best.  Work in a complete fertilizer like 5-10-5 before planting, or water in after planting with a high phosphorus (the middle of the three numbers) plant-starter fertilizer. Then, each month or according to fertilizer directions, apply a water-soluble fertilizer.

Geraniums are also ideal for containers. Use a sterilized potting medium, and top-dress with a slow-release fertilizer according to package directions. Water thoroughly when the soil is dry to the touch (so water comes through the drainage holes).

You can find more on annual geraniums from the National Garden Bureau (www.ngb.org).  Each year this organization of professionals picks a flower to feature, with 2012 being the Year of the Geranium.
   

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