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Gardening 101: Petunias

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Gardening 101: Petunias

July 11, 2018

Petunia, Petunia atkinsiana

Once again it is time to give a salute and thanks for the many stalwart garden plants we have inherited from our southern neighbors. Beauties that we commonly choose for dependable color and interest in our landscapes such as passionflower, fuchsia, nicotiana, nasturtium, alstroemeria, and many orchids were originally discovered growing as natives in the rain forests, and on the steppes and stony slopes of South and Central America. That also is true of the petunia, a plant that has been a favorite of gardeners since Queen Victoria was on the throne.

These days the cheery sight of petunias is so common that it’s easy to take them for granted. Let’s not. Read on to learn how these colorful flowers traveled to your garden (and how to help them flourish).

Photography by Britt Willoughby Dyer, except where noted.

Modern petunias have varied colors, stripes, and splotches thanks to centuries of hybridizing.
Above: Modern petunias have varied colors, stripes, and splotches thanks to centuries of hybridizing.

European plant hunters in the mid-1700s discovered petunias in South America and, after an introduction into Europe in the early 1800s, they quickly became a popular choice for the sumptuous flower gardens of the Victorian era.  However, those early petunias were not the lush, brilliantly colored blooms we know today.  The flowers were small, limited to either white or purple, and the plants themselves tended to be rather lanky and unimpressive.

For similarly splotchy purple and white petunias, consider &#8\2\16;Night Sky&#8\2\17;; \$6.75 at Select Seeds.
Above: For similarly splotchy purple and white petunias, consider ‘Night Sky’; $6.75 at Select Seeds.
Fortunately, by the late 1800s breeders in several countries including Germany, England, Japan, and the United States were hard at work to produce plants with larger blooms and an ever-widening array of colors and flower forms. Today the staggering number and variety of petunia hybrids continues to explode. Most petunias sold today in nurseries are varieties of Petunia x atkinsiana.

For a similar deep-pink petunia with subtle purple stripes, consider &#8\2\16;Sweetunia Suzie Storm&#8\2\17; (available seasonally for £\1\1.99 at Thompson-Morgan) or trailing petunia &#8\2\16;Shock Wave Deep Purple&#8\2\17; (\$4.49 for \1\2 pelleted seeds at Swallowtail Garden Seeds).
Above: For a similar deep-pink petunia with subtle purple stripes, consider ‘Sweetunia Suzie Storm’ (available seasonally for £11.99 at Thompson-Morgan) or trailing petunia ‘Shock Wave Deep Purple’ ($4.49 for 12 pelleted seeds at Swallowtail Garden Seeds).
The mainly funnelform (tube-shaped) blossoms can now range from one to five inches wide. Colors include the basic and ever-popular white as well as pink, red, lavender, magenta, yellow, purple, violet, and even black. Flowers are frequently striped, speckled, edged in a contrasting color (such as white or even chartreuse) or have centers that are round or star-shaped in hues either lighter or darker than the rest of the flower. To further boggle the mind, there are double blooms that look like miniature peonies and fancy varieties with dainty ruffled edges.

Mix-and-match petunias mingle with other flowering annuals in a hanging basket.
Above: Mix-and-match petunias mingle with other flowering annuals in a hanging basket.

Today’s gardeners and designers seem to be taking full advantage of the bounteous assortment of petunias available.  It seems that everywhere I walk here in New York City this summer, window boxes and containers of all shapes and sizes are overflowing with this fragrant flower. It is ubiquitous but, with so many pleasing forms and its ability to harmonize so beautifully with other annuals such as geraniums and salvias, petunias still manage to be fresh to the eye.

Petunias and red pelargoniums are happy companions.
Above: Petunias and red pelargoniums are happy companions.

Given the right conditions and some reasonable regular maintenance, this fragrant relative of the tomato, potato, eggplant, and tobacco will reward you with nonstop blooms well into fall.

Here are some tips if you would like to up the flower power in your garden with petunias.

Cheat Sheet

Begonias and petunias complement each other with their bright colors.
Above: Begonias and petunias complement each other with their bright colors.
  • Because petunias are good spreaders, they are excellent plants for hanging baskets, window boxes, and other containers where they will fill in abundantly, spilling over the edges and cascading down the sides.
  • Use petunias in the ground at the front of beds to soften the edges of walkways and as ground covers.
  • To keep your plant in constant bloom, you must deadhead rigorously. As soon as a flower begins to fade, pull off the entire bloom to prevent the plant from putting its energy into seed production.
  • Petunia plants can be cut back by as much as half in mid-summer to assure plenty of new flowers into the fall.
  • Petunias are perennials that are usually grown as annuals but they can be overwintered inside in a warm, bright location.

deep pink petunias by britt willoughby dyer

Keep It Alive

  • To ensure the most prolific flowering, plant in a site with at least five to six hours of full sun and initially pinch back the growing tip to encourage a bushier habit.
  • Petunias will tolerate poor soil but prefer a light growing medium that is moist but well-drained.
  • Water regularly, especially during hot dry summer weather, but don’t allow the plants to sit in soaking wet conditions.
  • Avoid dousing petals when you water to prevent damage to the flowers.
  • Petunias are delicate so a sheltered location out of strong winds is recommended.
 In general petunia cultivars fall into two major categories: Grandiflora and Multiflora. Grandiflora petunias have large flowers, typically at least four inches across, but are susceptible to damage from rain which can reduce the petals to a sodden mess.  If your climate tends to be rainy, put these plants in a sheltered spot. Multiflora petunias have smaller flowers but bloom more abundantly and are usually better able to stand up to adverse weather conditions such as rain and wind.
Above: In general petunia cultivars fall into two major categories: Grandiflora and Multiflora. Grandiflora petunias have large flowers, typically at least four inches across, but are susceptible to damage from rain which can reduce the petals to a sodden mess.  If your climate tends to be rainy, put these plants in a sheltered spot. Multiflora petunias have smaller flowers but bloom more abundantly and are usually better able to stand up to adverse weather conditions such as rain and wind.

Calibrachoa

Calibrachoa flowers are almost identical to petunias but are smaller, bloom more vigorously and are available in an even wider variety of colors and patterns. Photograph by Cliff Hand via Flickr.
Above: Calibrachoa flowers are almost identical to petunias but are smaller, bloom more vigorously and are available in an even wider variety of colors and patterns. Photograph by Cliff Hand via Flickr.

A discussion about petunias would be incomplete without mentioning one of its relatives that is rapidly giving the petunia a run for its money as a popular container plant. Calibrachoa is a native of Brazil and migrated here in the late 1980s and early 1990s after Japanese hybridizers made some improvements that made it easier to grow.

Ellen Reznick of Lush Life Gardening, who uses many annuals in her work beautifying New York City terraces and balconies, told me she avoids petunias in favor of calibrachoa because it flowers more generously and is impervious to some of the cultivation problems of petunias (including mildew and susceptibility to weather damage). The good news is that gardeners have an ever widening array of choices of beautiful plants. The bad news is…so many decisions.

See more growing tips in Petunias: A Field Guide to Planting, Care & Design in our curated guides to Annuals 101. Read more:

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