University of Vermont Extension
Department of Plant and Soil Science
Leonard Perry, Extension Professor
University of Vermont
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.
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
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
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
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.
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.
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
pelargonium that we have to thank for the seeds we buy in catalogs
recently, many geranium plants we find for sale are once again
propagated. Many of these are from
improved series, crosses among two or more species or types of
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.
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.
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).
this organization of professionals picks a flower to feature, with 2012 being
the Year of the Geranium.