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Plant of the Week: Petunia, Garden

The University of Arkansas System Division of Agriculture does not promote, support or recommend plants featured in "Plant of the Week." Please consult your local Extension office for plants suitable for your region.

Plant of the Week

Garden Petunia
Latin: Petunia x hybrida

Picture of white and pink Garden Petunia flower.

Last July, as my friends and family sweltered in the heat of an Arkansas summer, I had the rare treat of watching icebergs float into Spaniard’s Cove on the northeastern coast of Newfoundland. The presence of these summertime bergs is not uncommon in Canada’s far north.

But, while I was watching the ship-size burgs, news reports mentioned that a mammoth hunk of ice had recently broken free of the permanent ice shelf between Canada and Greenland. That was new and another indicator that global warming was a fact, not the fantasy of fear-mongering environmentalists.

During my college years, a topic of great interest in horticultural research was fertilizing greenhouse plants with carbon dioxide. The principle guru of this movement was Dr. Marc Cathey, the lead USDA research scientist for greenhouse crops. Cathey, an extreme extrovert and consummate showman, went on to become the long-serving president of the American Horticultural Society and was instrumental in the growth of that organization during the past couple decades.

One of Cathey’s favorite test plants for showing the increased growth elevated carbon dioxide levels could produce was the garden petunia. By doubling or quadrupling the carbon dioxide level, petunias literally jumped out of the ground. Growth rates increased dramatically but then leveled off, only increasing further if the light intensity and temperature were increased.

In the mid 60s when Cathey was conducting his research the concentration of this important gas was 285 parts per million (ppm). Today, a scant 40 years later, the ambient concentration of carbon dioxide stands at 340 ppm, an increase of about 20 percent during my working career.

Glacial deposits contain pockets of trapped gasses and serve as a convenient means of looking at carbon dioxide levels over time. Levels began to increase by the end of the 19th century as the Industrial Revolution picked up momentum, but the rate of increase really took off after WWII.

As the level of these and other trace gasses increase, heat is trapped in the earth’s atmosphere. Just as the night temperature is warmer on a cloudy night, these gasses cause the average temperature of the earth to increase. Over the last century the earth’s average temperature has increased 1.1 degrees Fahrenheit, with most of that increase coming since 1970. The 1990s was the hottest decade in the last thousand years.

Claims by politicians that such changes are part of the "natural" cycle are disingenuous and fly in the face of common sense. The car culture and petroleum based industries that swept our nation in the 20th century are now a world-wide phenomena. Emerging nations are all vying for their share of the good life, while our political leadership hunkers down and passes the problem on to future generations. The Kyoto Protocol, while undoubtedly far from perfect, is at least a start in addressing this issue on a global basis.

To gardeners, global warming is not all bad. Plants do grow better and faster with higher carbon dioxide levels. Dr. Cathey has not been idle in his retirement. In the mid-90s he developed the Heat Zone Map that gave gardeners a means of determining the southern limits of plant hardiness.

This year, the American Horticulture Society will be releasing, along with the USDA, its new plant hardiness zone map based on weather data collected from 1990 to 2003. The new map uses the same dozen hardiness zones, but because of the milder winters we have had during recent years, each zone has shifted further north.

The previous map had Arkansas divided into three zones, 6, 7 and 8. The new map has the state divided into just two, zones 7 and 8. Little Rock is now considered zone 8, while Fayetteville moved to zone 7.

I’ve always wanted to grow gardenias, and now thanks to global warming, they should do just fine in my garden.

By: Gerald Klingaman, retired
Extension Horticulturist - Ornamentals
Extension News - January 16, 2004


The University of Arkansas Division of Agriculture does not maintain lists of retail outlets where these plants can be purchased. Please check your local nursery or other retail outlets to ask about the availability of these plants for your growing area.