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Petunia sp. Juss. 1803
pronounced: pet-YOO-nee-uh species
(Solanaceae – the nightshade family)
common name: Petunia
Most of the petunias seen in our gardens are hybrids (Petunia X hybrida). This is thought to have come from the hybridization between Petunia axillaris (the large white or night-scented petunia) and Petunia integrifolia (the violet-flowered petunia). The former, which was first sent from South America to Paris in 1823, bears night-fragrant, buff-white blossoms with long thin tubes and somewhat flattened openings. The latter has a somewhat weedy habit, spreading stems with upright tips, and small lavender to purple flowers. It was discovered in South America by the explorer James Tweedie, who sent specimens to the Glasgow Botanical Garden in 1831. Many open-pollinated species are also gaining popularity in the home garden. A wide range of flower colours, sizes, and plant architecture is available in both the hybrid and the open-pollinated species.
At the beginning of the 20th century, breeders in Japan began researching petunias, and in 1935 Sakata Seed Corporation bred the first consistently fully-double petunias. ‘All Double Victorious’ mix was considered a breeding break-through. The flowers were as large as the double petunias of today. It was a grandiflora type with fringed petals. The Sakata people managed to interpret and apply Mendel’s law of gene dominance in the search for a fully-double petunia, one that would come true to type from seed. During the 1930s, German seed companies bred grandiflora varieties, and greatly expanded the diversity of the plants, especially in the area of colours. The 1939 Benary Seed Growers catalogue offered an open-pollinated, dark purple, white-edged petunia, but it was not until the 1990s that this unusual bicolour combination was introduced as a hybrid. The history of the hybrid petunia involved an exchange of information – individuals and companies learning from, and building on, what others had done.
In the late 1930s, Charles Weddle, of W. Atlee Burpee & Co., applied the same Mendelian law in his search for the fully double petunia. When he discovered the key – that the gene for doubleness was a dominant gene, and crossing a true-breeding double-flowered petunia with a compatible petunia would yield seeds that produced all double-flowered offspring – the production of modern-day petunias was on the way.
After the interruption of World War II, work began again in earnest. Doubleness wasn’t the only characteristic breeders were looking for. They also wanted larger flowers, and more of them for a longer time, more compact plants with better branching habits, and better disease- and weather-resistance – many petunias, even today, look bedraggled after heavy rain. Fred Statt, of Harris Seeds, worked on disease resistance, while still coming up with petunias that looked beautiful. And so the tale goes on, right up to the present-day, as breeders look for even more beautiful and unusual flowers.
There are 4 main categories of petunia:
(i) Grandiflora: these have the largest flowers, up to about 10 cm in diameter. They have the widest variety of forms and colours, but are most likely to be damaged by heavy rain or watering. Some of them are cascade selections, well-suited to growing in hanging baskets, window-boxes and other types of planters.
(ii) Spreading: these are characterized by their low height (usually about 15 cm) but large spread (1 m or more). Given adequate water and fertilizer, these make a very effective ground cover.
(iii) Multiflora: these are about half the size of grandiflora, are not easily damaged in heavy rain, and can tolerate more sun.
(iv) Milliflora: the flowers of these are only about 2–3 cm, and are prettiest when mixed with other plants. They tolerate harsh weather quite well.
Most petunias are low, spreading plants with simple, rounded, downy dark green leaves and trumpet-shaped 5-lobed flowers. They come in a range of colours from white, pink and red to blue and purple, often with a variety of multi-coloured markings, and with either single or double blooms. The wild species are often aromatic, with scented flowers. but, as is often the case, many of the fancy garden forms have lost these charms, though they compensate with an abundance of blooms and a wealth of colour.
‘Pinching’ the plants can be done to increase the number of flowering stems and discourage excessive leaf growth. Dead-heading the old flowers will encourage repeat blooming.
As well as their uses in the garden, petunias make excellent cut flowers: the more you cut, the more the plants seem to produce. Because their stems are somewhat lax and their leaves are sticky, the flowers are best cut with short stems.
The petunia is surely one of the most popular annual flowers ever to grace our gardens, porches and patios. Whether edging a flower-bed, covering a bare area, spilling out of a container or trailing from a hanging basket, petunias help to keep the gardening season at its most colourful for the longest possible time.
Photographs taken in Picnic Bay 2008-2010
Page last updated 15th January 2017