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Plant of the Week
Zonal Geranium
Latin: Pelargonium x hortorum
 Geraniums
are a common part of the garden scene in Arkansas with a long history of
cultivation and thousands of selections to choose from.
Zonal geraniums have been grown in Europe since 1632 when John
Tradescant, the gardener for Charles I of England, took the plants back
to Europe from their native South Africa.
A gardener working for Napoleon’s Empress Josephine, is credited with
producing the first hybrids in the late 1700s. But it wasn’t until the
early 19th Century, during the great horticultural craze for new plants,
that the modern day geranium in all of its varied forms came into being
through hybridization. During that era -- if the modern day university
system had existed – there would have been a Department of Geraniology
to study this exciting new group of plants.
The geranium is, in nature, a hardy shrub with fat, succulent stems that
evolved in the dry, frost-free highlands of South Africa, where
temperatures are moderate during the growing season. The old practice of
knocking soil from the roots and hanging the plants under the house for
the winter is an acknowledgment of the geranium’s ability to survive
periods of drought and neglect. The zonal geranium of today, so called
because of the band or maroon that forms a circle on the leaf, is
available in a wide array of colors ranging from white to pink, red and
orange. Red is the most common color.
For as tough as geraniums are in the garden, they are rather difficult
to produce on large scale as is done for the greenhouse industry. Before
WWII, most greenhouse growers maintained a few geranium stock plants to
use for producing cuttings the following spring. In the years after the
war, it was realized that geraniums could be grown in Southern
California with cuttings shipped nationwide, thus eliminating the need
for growers to maintain their own plants.
This method worked well for a few years, until a wet year in the early
1950s in the geranium growing area resulted in an outbreak of a
bacterial disease. Plants infected with geranium blight were sent
throughout the country, and within a few years almost all geranium
plants were showing symptoms of this serious disease that quickly killed
infected plants.
Growers, working with plant pathologists, quickly developed a way of
indexing their plants to see if they were free of the bacterium. Once a
group of plants was shown to be disease free, they were used as the
stock plants for propagation. The same procedure is still used today but
most geraniums today are grown in Mexico with unrooted cuttings shipped
to stateside growers.
Geraniums love bright sunlight, but they don’t like it too hot. When the
temperature is above 95 degrees Fahrenheit, they stop flowering. If the
temperature persists too long, they may even turn yellow.
In Arkansas, they are usually at the best in the spring and early summer
and fall – July and August are just too hot for them to flower
consistently. Because geraniums have been highly hybridized, they
require frequent fertilization to keep them in active growth and
producing lots of flowers. Once the flower head begins to fade, they
must be removed to keep the plant tidy and to keep future blooms coming.
By: Gerald Klingaman, retired
Extension Horticulturist - Ornamentals
Extension News - February 26, 1999
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