Annuals A - Z: All About Annual Flowers & Plants, by Graham Rice

Discovering Annuals, by Graham Rice

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Petunias - their history and use in the garden

From The Garden

Everywhere you go, all over the world, you see petunias. They are especially popular in areas with dry, sunny summers including many parts of the United States, Australia and South Africa and in northern Europe too they are amongst the most popular of summer flowers.

Since the arrival of the prolific and vigorous trailing types raised from cuttings, in particular the Surfinia Series, petunias have achieved an even higher profile through their popularity in window boxes and hanging baskets, both in home gardens and often more visibly on pubs and bars, offices and in municipal plantings for city centres.

Rather surprisingly at first sight, petunias belong to the potato family where their closest relatives are Nicotiana and Cestrum. In 1985 it was suggested that the genus name itself, Petunia, was invalid and that the correct name should be Stimoryne. Fortunately, the rules of the International Code of Botanical Nomenclature allow invalid names to be retained for well-known plants with a strong commercial significance and so an outcry from gardeners everywhere was prevented and the name Petunia persists.

The garden cultivars are grouped under P. x hybrida, the parents of this huge group of hybrids being forms of just two out of about 37 wild species from tropical South America. These are the white P. axilliaris, (previously known as P. nyctagiflora) and the purple P. integrifolia (P. violacea).

Like so many of today's summer bedding plants including pelargoniums and salvias, in gardens petunias behave as tender perennial plants, albeit sometimes rather short-lived. However their rapid growth and ability to flower prolifically on young plants allows them to be raised from seed as half hardy annuals.

The ease with which they root has always allowed unusually good forms to be grown from cuttings and in the nineteenth century, before plant breeders had stabilised the different colours and forms sufficiently to be dependable from seed, this was commonplace.

It was especially useful for the double flowered forms as only 20-40% of seedlings produced double flowers. So the best doubles were propagated vegetatively and, because they were highly susceptible to rain damage, in the UK they were most often grown in the greenhouse or conservatory.

Petunias from seed

The transformation in the quality of petunias came with the development of F1 hybrids. This made it possible for their habit to be improved and their rather open, floppy growth to be replaced by a bushier form creating a bolder impact and being better able to stand up to the battering of a summer out of doors. At the same time they were increasingly bred with weather resistance in mind, an ever increasing range of colours and colour combinations were created and cultivars also began to be more clearly categorised as Grandiflora or Multiflora types. The situation has recently become more complicated but can be summarised as follows.

Grandiflora petunias have large flowers and are best suited to settled, sunny summers and protected situations in other areas; they dislike dull, damp and windy conditions. Breeders have worked intensively improve the weather resistance of their large flowers and trials have seen in the last two summers have shown that the Storm Series, in lavender, salmon and rose, represents a significant step forward.

The other leading series are the spreading Supercascade Series in nine colours, the Falcon Series in twenty one colours, the veined Daddy Series in six colours and the improving Prism Series in thirteen colours.

Multiflora petunias have smaller flowers, but usually in greater numbers. Recovery after bad weather has been constantly improved along with the weather resistance of individual flowers, partly by selecting for a waxy epidermis which sheds the rain from the petals. The leading series are the Carpet Series in fifteen colours and Prime Time in twenty four colours.

Doubles now feature in both groups and modern series like the Duo Multifloras in seven colours and the Pirouette Grandifloras in purple and rose can be relied upon to produce 100% double flowers. The Duos in particular are significant advance, featuring unexpectedly good weather resistance.

More recently the boundaries have become less clear. Not only does the Storm Series of show markedly improved weather resistance but the goal of good weather tolerance and large flowers has also been approached from the other angle. New, larger flowered Multifloras, sometimes classified as the Floribundas, feature the weather resistance of the Multifloras but with larger flowers. The Celebrity Series in twenty colours and Mirage series in nineteen colours lead the way here.

The most recent innovation in F1 hybrid seed raised petunias has been the seven colour Fantasy Series. These are strikingly different, with noticeably small flowers on small rounded plants generally more suited to containers than open ground plantings.

There is fierce competition between petunia breeders around the world in the development of new flower colours and colour combinations. It has still proved impossible to completely stabilise the white-edged picotee types and the white-starred types, but their patterning is steadily becoming more stable in difficult growing conditions.

Yellow throated types, sometimes referred to as morn or halo types, are the latest popular colour combination and feature in a number of series. Horizon Lavender Sunrise is an especially striking example of this type, lavender pink with a yellow throat, but is so bold as to be almost impossible to place effectively in the garden.

Yellows have always been especially difficult in less than perfect conditions but 'Carpet Buttercream' (Multiflora) and also 'Prism Sunshine' (Grandiflora), launched at this year's Chelsea Flower Show, represent significant improvements. 'Prism Sunshine' is a spectacular yellow and already a Fleuroselect Gold Medal winner and an All-America Selection. A startling scarlet-veined white form will be the next breakthrough to appear.

Petunias from cuttings

Much to many people's surprise, the most recent innovation in petunias has been the revival of raising them from cuttings. The vigorous trailing types, typified by the well known Surfinia Series, have been an outstanding success, in spite of problems of virus infection now prevented by cleaner stock, better screening and improved nursery practice. Plants have of this type had been discarded by breeders for many years until their potential was finally spotted by a Japanese company but so far the seed breeders have found this type difficult to stabilise, hence the use of vegetative propagation.

They make spectacular sheets of colour trailing from window boxes and baskets, although their tendency to simply hang down vertically makes them difficult to combine with other plants. They are greatly underused as ground cover both in parks and in new gardens where a relatively small number of plants would make an impressive show while permanent plantings are becoming established.

New cultivars of this type from Israel have proved themselves both more prolific and less straggly and these will be appearing in garden centres this summer. Doubles and yellows are on the way but this year has also seen a return to the Victorian approach with the introduction of double flowered petunias raised from cuttings.

'Priscilla', a prettily veined form with a more spreading, less vertically trailing habit and the bushier 'Abel Mabel', a sumptuous reddish purple with dark veins, are the first in two new series of doubles. It is important to note that almost all these trailing, cuttings raised petunias are protected plants and cannot be propagated for sale without a license.

We have also seen first seed raised plants of this type. 'Purple Wave' and 'Pink Wave' have proved highly successful, if expensive, introductions, and are valuable both as trailing plants for containers and as ground cover where they are especially spectacular and make a stunning carpet on sunny banks.

Petunias in the garden

Given just one unshakeable requirement, plenty of sunshine, petunias are adaptable plants in the garden. Until the arrival of the Surfinias, the Supercascade Series of Grandifloras was the standard for baskets and window boxes and its spreading rather than strongly trailing habit combined with its large flowers created spectacular displays in situations where the flowers were not overexposed to rain or wind. The Storm Series is a more weather resistant newcomer but we await a full range of colours.

Where a bushier habit combined with more weather resistant flowers is required for containers, plants from most Multiflora and Floribunda series will fit in better with other plants like trailing lobelias, silver-leaved helichrysums, ivy-leaved geraniums and verbenas. Even these, however, can overpower some plants sold for use in baskets such as the double Lobelia 'Kathleen Mallard', bacopas and the smaller nemesias like 'Joan Wilder'.

The Wave and Storm series also make startling ground cover plants in full sun, although the extent of their spread makes them better suited to large scale parks and municipal planting than small home gardens.

For summer displays in home gardens the Multifloras and Floribundas are the most dependable and one most useful developments is their increasing availability in separate colours, especially as seedlings and young plants in garden centres. This enables gardeners to get away from unpredictable spangly mixtures and use petunias in planned bedding arrangements. It is also worth searching the garden centre displays of pot grown mixed petunias and picking out especially attractive shades.

So the gorgeous soft, but not quite sugary, pink of 'Celebrity Chiffon Morn' with its palest primrose throat is pretty in a pastel arrangement with the silver foliage of Plecostachys serpyllifolia or Helichrysum petiolare 'Goring Silver' and with red dianthus and white phlox plus the taller spikes of rose pink Sonnet antirrhinums.

The rich purple-blue of 'Mirage Midnight' looks splendid in a sultry harmony with the bronze foliage of Hibiscus acetosella 'Red Shield' and 'Bulls Blood' ornamental beet plus heliotropes like 'Chatsworth'. Sparks of golden yellow from Tagetes 'Tessy Gold' or the vivid trailing shoots of Helichrysum petiolare 'Limelight' make more striking additions.

First published in The Garden (the Journal of the Royal Horticultural Society), Julne 1997

 Petunia A-Z


©copyright 1997 Graham Rice. All Rights Reserved. All Images Digitally Watermarked.

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