University of Vermont Extension 
Department of Plant and Soil Science

Spring News Article
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CHOOSING, GROWING AND USING PETUNIAS


Dr. Leonard Perry, Extension Professor
University of Vermont


Petunias are among the most popular annual flowers purchased each spring and summer.  One reason is that they come in a wide range of flower colors and shapes.  They range in habits from mounded—good in masses or “bedded out” as bedding plants, to trailing—good in raised beds, pots, and hanging baskets.  Petunias are easy to grow, meaning they have few if any pest and disease problems, are adaptable to many climate and soil conditions, and require minimal maintenance. 
           
Petunias are members of the Solanaceae or nightshade family, which includes tomatoes, peppers, potatoes, tobacco, and flowers such as flowering tobacco and Angel’s trumpet.  This favorite annual flower was first discovered in South America more than two centuries ago. The earliest petunias were small-flowered and lanky and were found in only two colors, white and purple. But even as early as the beginning of the nineteenth century, European breeders were experimenting with crossbreeding to develop larger flowers and more colors.
           
Today, petunias are available in shades of white, yellow, pink, blue, purple, red, and even black, as well as bicolors, and as single or double flowers. Many have a light, sweet fragrance, especially the blue petunia varieties. Petunias will last four to six days as cut flowers too.  
           
With so many colors to choose from, petunias are fun to combine into designs.  For a more striking effect, combine contrasting colors such as yellow and purple, red and white.  Or combine a bicolor star pattern of purple and white flowers with solid purple ones.  For a more subtle effect, combine shades of one color, as a bed of pink petunias with a few darker red ones.
          
Petunias combine well with other annual flowers too, such as purple or white alyssum with purple or white petunias; yellow lantana with reddish verbena and lavender petunias; white fan flower, pink twin flower, and lavender petunias; bright pink petunias with dark foliage, as from the sweet potato vine.
           
Most gardeners buy flowering plants in small pots or cell-packs, but you could grow your own petunias from seed if you plan ahead.  Sow seed indoors eight to 12 weeks before the average last-frost date in your area. Since seeds are so small, sometimes you may find them “pelletted” with a casing to make them larger and easier to handle. Sow on the surface and lightly press in, but don’t cover as they need light to germinate.
           
When buying bedding plants, look for plants with healthy foliage and plenty of buds. There should be no signs of dried out or spotted leaves or diseases.  Make sure soil in containers isn’t on the extremes—too waterlogged, or dried out. 
           
When buying, and later at home, watch for a whitish growth on leaves which is likely powdery mildew.  If you find a grayish growth on leaves and flower buds, this is likely botrytis disease.  Both diseases signal improper culture, particularly lack of air circulation and too moist conditions.   The latter can happen from watering too late in the day, the plants staying wet overnight.
           
For container planting, use a soil-less potting mix. If you're planting petunias in the ground, choose a location with light, rich soil and good drainage. Space plants about a foot apart for the mounded types, up to 2 feet apart for trailing types.  Pot labels should give you an idea on spacing. Work in some peat moss or compost before planting. Mulch to help keep down weeds and retain soil moisture.
           
Petunias prefer full sun (over six hours a day) but will tolerate partial shade of 4 to 6 hours daily of direct sun. However, in part shade the plants will flower less and get leggy.
           
These summer annuals are drought-tolerant, so once established and growing don't worry about watering unless there are prolonged periods of drought. Window boxes and containers, especially those located under overhanging eaves, should be checked daily, however, and watered as needed as the soil tends to dry out more.
           
Petunias require little care but will benefit from fertilizer. Use according to the label directions on your product of choice.  Those you grow from seeds may require a bit less than those you buy in pots, which are often grown from cuttings and bred to need more fertility.  If plants grow slowly, have few flowers, or light green to yellowed leaves, and all other culture and conditions are right, then plants may be hungry and need more fertilizer.

In the past, most cultivars (cultivated varieties) would bloom, then need cutting back, and would then rebloom in a few weeks.  Others might bloom longer, but needed old flowers pinched off or “deadheaded” after bloom.  Most new varieties that you find now for sale or from seeds need neither, older flowers just fading away and dropping off on their own, with a continual show of new flowers.  This particularly applies to the smaller flowering selections.  You may want to remove spent flowers from the larger flowering (“grandiflora”) and double types to keep them blooming longer, and more attractive.

Each year the National Garden Bureau chooses an annual Flower of the Year, the one for 2014 being the petunia.  Visit their website to learn more about the history and many types of petunias, as well as other popular vegetables and flowers (www.ngb.org/).

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