Green Thumb – Petunias

Posted: July 19, 2023

Petunias are better than ever

Who can resist the bold splash of color in a border of blooming petunias or in a hanging basket loaded with flowers?

New petunia colors are bright and lively, gorgeous and garish. Breeding has made them more vigorous, with stable flower patterns and colors, and a greater tolerance of weather extremes. Some of the new names like ‘Hells Forge’ and ‘Crazytunia Mayan Sunset’ can make you stop in your tracks.

These beauties had a humble beginning. Spanish explorers in the sixteenth century discovered them in South America and considered them too ugly to collect. The locals called them “Petun” which roughly translated as “worthless tobacco plant.” A Scottish explorer in the early 19th century found and collected other species. By the end of the century, breeders in England, Germany, America and Japan began cross-breeding them to create a diversity of colors and blooms.

Petunias are organized in categories based on their flower size and growing habit.

Grandiflora petunias produce large flowers. They may be singles or ruffled doubles. Some have a cascading habit that makes them look good in hanging baskets and window boxes. Most are upright plants that develop into large mounds of flowers 12 to 15 inches tall.

Multiflora petunias are smaller plants with smaller flowers. They make up for their size with many blossoms that open at the same time. Single flowers are the most common, although there are some doubles available. When massed together they make an eye-catching statement in the garden.

Milliflora petunias are miniature plants that produce an abundance of small flowers about an inch in diameter. They make nice edging plants and also look good when mixed with other flowers in a container.

Spreading petunias make a great groundcover. They grow about six inches tall, but spread rapidly to cover a large area, provided they’re watered and fertilized frequently. They are ideal in a hillside garden, or on top of a retaining wall. In hanging baskets and window boxes, they trail several feet over the course of the summer.

Photos courtesy of Janice Weber

The best advice about growing petunias is to give them lots of sun, at least five or six hours a day. In the hottest part of the summer they will look their best if they can get partial shade from the strong afternoon sun.

It’s important that the soil they’re planted in drains well. This is especially true if your soil is heavy clay. Incorporate peat moss, compost or manure.

Thorough watering once a week should be sufficient, except in very hot weather. Spreading types need more frequent watering, and petunias in containers may need to be watered every day. Like many annuals, they don’t like to be dry for too long.

In early July begin to fertilize them every two weeks with a fertilizer meant for flowering plants. If you are growing the spreading type, fertilize them weekly.

Although many petunias are described as “self-cleaning” it helps to remove faded flowers, but be sure to include the part below the blossom where the seeds form. It’s not practical to do this on a bed of petunias, but it’s good maintenance when they’re growing in containers. It helps prolong blooming and keeps the plants looking their best.

The word “unique” is no longer adequate when describing the new varieties. They have earned superlatives like “flamboyant,” “ostentatious” and “eye-popping.” Enjoy the new beauties being introduced each year.

For more information about growing petunias visit https://extension.umn.edu/flowers/growing-petunias.

Janice M. Weber – University of Illinois Extension, DeKalb County Master Gardener


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