Petunias are a favourite bedding and container plant for warm weather colour. In regions with drier, sunny and warm summers such as Australia, southern Europe, and much of Africa, New Zealand, North and South America.
Petunias are often the top-selling bedding plant of the Summer season. Petunias are usually treated as annuals but are actually herbaceous, evergreen, rather weak-stemmed, short-lived perennials or sub shrubs native to South America, particularly Argentina and Brazil. In their native environment they are commonly known as ‘Sunweeds’: sprawling open-growing plants with disc-shaped, single, trumpet flowers in mauve, blue, lilac, magenta and purple that act as excellent groundcovers in dry and sunny spots.
Their name ‘Petunia’ is a Latin version of a South American vernacular ‘Petun’ meaning “tobacco” to which they are allied. They are classified as members of the Solanaceae Family which includes Calibrachoa, Chilli Peppers, Potato, Tomatoes and the large Nightshade Family. Thus anything that successfully feeds these related botanical Family members can be used to fertilise Petunias.
Petunias are usually started fresh each year from seed. Seed can be sown from Early Spring through Mid Summer up until there are 4 months or more of frost-free weather ahead. They can also be grown and flowered almost year-round very successfully in the sunny glasshouse.
Seed is very fine and should be sown thinly over moist but porous seed raising mix. Barely cover the fine seed and keep bright, humid, moist and warm. Minimum temperature for successful germination is 65F/18.4C or preferably warmer. Sow seed into seedling flats or individual containers. Seed containers are often covered with a sheet of glass and placed in a bright warm environment, on a sunny bench in a heated glasshouse or over heating cables to speed germination. Avoid chilling and over-watering as seed will surely rot! Seed has a much better chance of germinating if it remains too dry rather than too wet.
Seed germination is often erratic or slow, especially if conditions are cool. Once seed germinates maintain very bright light so that seedlings do not ‘stretch’ and weaken. When seedlings have attained at least two sets of mature young leaves, they can be transplanted into individual containers for growing on. Or in ideal conditions they can be transplanted into the garden.
Maintain bright and warm conditions with light, liquid feeding and watering plus very good air circulation. When plants have reached 3-6in/7.5-15cm they can be hardened off in protected outdoor conditions. Within the following week or two they should be strong enough that they can be transplanted into their permanent flowering positions. Plants become much bushier and more prolific if the first central flower bud and growing tip is pinched out. This is can be done while growing-on in their containers or when each seedling is transplanted.
When transplanting Petunias, this is best done during cloudy and/or damp weather without much wind so that they do not collapse and wilt. Once transplanted, water in well and make sure that young seedlings do not dry out until they become established.
For really bushy plants, continue to pinch or shear plants back several times to create numerous side shoots. Larger Grandiflora forms flower better and for longer when old seed pods are removed. After a big flush of flowers has finished, once again pinch or cut the plants back; provide a liquid fertiliser and good watering if conditions are dry and a new flush of flowers should soon follow.
Many gardeners prefer to liquid feed with a high phosphate fertiliser as the buds begin to form. Avoid overfeeding with high nitrogen fertilisers. This produces masses of leaves but fewer flowers. Water regularly and deeply during dry weather. Flooding the bed is often the best way to avoid bud rot and muddy, spotted flowers. Be warned that snails and slugs adore petunias as much as we do.
Being soft perennials, most all Petunias can also be started from cuttings taken during the warmer months from Spring through Autumn. These cuttings can often be obtained when the plants are being pinched or sheared back. When grown from seed Petunia offspring can be somewhat variable. So whenever a particularly fine cultivar is struck, it can be perpetuated by cuttings. Cuttings taken early in the season will flower the same Summer and Autumn. Late Summer or Autumn cuttings of especially fine cultivars can be wintered-over in the glasshouse.
Petunias are sun-lovers, preferring as much direct sunlight and warmth as possible. But they will also thrive under rather cool conditions provided the plants remain dry and sunny. They are natives of quite arid and drier regions from cool, rocky highlands to semi desert lowlands. Provided that the plants stay rather dry and/or very well-drained, they are not particular about soils. Petunias can be successfully grown and will often thrive in anything from course gravel and light sands through most standard garden and potting mixes and even in fairly heavy clay.
Because Petunias originate from rather arid and drier areas with poorer soils, they can be grown with less feeding. Overly rich soil often will produce much more foliage than flowers so beds or containers should not be over fed and never overwatered!
But they respond well to the addition of well-rotted manure, especially Horse manure, or mature compost. Also they thrive with the addition of a good well-balanced general Garden Fertiliser or one used to feed Tomatoes. They do prefer soils generously enriched with Lime. All soil additives are best added and dug into the soil a week or more before planting.
The big secret to success with Petunias is the ‘dry’ aspect. No matter what kind of feeding or soil they have, if conditions remain damp, humid, poorly drained, water-logged or constantly wet, they will either perish, rot or their blooms will disintegrate into mush.
The biggest problem with petunias is their need for sustained heat: the hotter the growing situation, the better. Growth and flowering greatly increase when temperatures remain above 21 C /70Fdegrees, especially at night. Since this seldom happens in New Zealand's cool climate or in many other temperate climates with a limited growing season, seed is usually sown under glass with bottom heat in Late Winter or Early Spring. Seedlings are then ready to plant outdoors once the weather and soil have become sufficiently warm.
Best results often come from beds enriched prior to planting with a heavy dusting of lime mixed with compost; phosphate (superphosphate, phosphate rock, etc.) for bigger blooms with substantial texture; and potash (sulphate of potash or wood ashes) for more vivid colours, especially blue and purple shadings. Plants that appear weak can often be revived with a dusting of lime mixed with a little blood and bone. Simply sprinkle this enriched fertiliser dust over, or best, around the plants. Water it in thoroughly during bright or sunny and warm weather.
A little Magnesium Sulphate (Epsom salts) and/or trace elements mixed in with this fertiliser or into their water will further boost the plants. Copper sprays will stop any fungus. Petunias are excellent plants for hot dry spots where other flowers are often sun-burned. The dwarfed varieties and many species are excellent in coastal and quite windy sites as well as in containers and tubs or window boxes. The cascading Petunias originate from climbing, creeping, scrambling and over-all taller-growing species. These often damage easily under windy conditions, especially if the plants are brittle from cold and wet weather, but make ideal cascades in baskets, containers, terrace walls and when used as a bedding plant, groundcover or sub shrub amongst perennials and low shrubbery.
Early plantings put in after all danger of frost has past usually create the best displays because they mature in the peak of Summer heat. In very warm, sheltered sites seed can be sown directly into the garden or into containers. This provides a later show of colour provided they are not the victims of an early cold snap or cool Autumn rain. In colder districts try planting into an enriched bed covered with a sheet of black weed mat. This will maintain warmer soil temperatures and produce a much better, longer lasting display.
Petunias resent cold, although many hybrids tolerate cool and drier weather. Some varieties will withstand mild frost but almost all are killed by a freeze. But the biggest killer is wet feet, especially if conditions remain cloudy and cool. Petunias demand near perfect drainage. Plants do best when grown in a soil that stays constantly on the faintly moist side of dry. They often fail in baskets, tubs, or other smaller containers that must be frequently watered. Sometime there can be a problem when the soil contains water-retentive granules or too much peat that maintains a sodden soil. Some of the newer hybrids bred from hardy species like the “Wave Series” have been especially bred to tolerate container culture and liquid feeding.
But many of the finest, large-flowering, traditional Petunia hybrids ultimately fail when grown in containers because under these conditions the plants are subjected to extremes of dry followed by chilling wet feet that often lead to root rot. If planting Petunias in a container choose a larger size that assures more constant conditions. When choosing the site for this container avoid sites subjected to continual drying or chilling winds and very hot positions which would place the Petunias under stress caused by these extremes. And make sure that if they must be frequently watered to maintain their flowering that this water can drain away quickly and preferably stay off their delicate blooms.
Less than one hundred and fifty years ago there were only a few distinct species and varieties available. Most were single, trumpet shaped flowers in white or soft pastel shades. Petunia integrifolia was the first species to be sent to Paris in 1823 and the United Kingdom a few years thereafter. These were mostly sprawling, scrambling or nearly vining plants with lightly fragrant simple trumpet-shaped lavender, mauve or purple flowers. Today there are perhaps 30 recognized Petunia species and cross breeding between the wild species and their progeny have resulted in many hundreds of named hybrids from miniatures, dwarf bedding types, bush varieties to 50cm/20in. cascade and balcony trailers and climbers to over 2m/6+ft.
Petunias can be classified in several groups or ‘series’ dependent on their habit of growth and flowering:
Grandiflora Petunias are the giants of the group. They feature blousy blooms that can reach 4-6inches/10-15cm in diameter or more. Many are quite fragrant, especially in the evening. There is a wide range of colours and forms. Plants are fast-growing, robust and spreading. Usually the plants are 15-18in//37.5-45cm tall and often spreading that wide or sprawl much wider. The largest and often quite spectacular ‘Cascade’ Petunias and their hybrid forms are included in this group.
Popular named Grandiflora hybrids include:
‘California Giant Series’. These are very fast-growing, robust, sprawling and spreading or sometimes climbing or cascading plants often 1m/3.34ft or more with fleshy, thick stems and leaves that are often sticky. Very large, disc-shaped, open trumpet blooms produce waving margins sometimes with flecked colours and exquisite veining usually in deeper complimentary colour shadings. Plants are quite hardy and can withstand considerable cold although blooms will suffer. California Giant Petunias are easily propagated from cuttings or seed.
‘Daddy Series’ (mauve, pink and purple shades with a darker centre often with attractive veining); ‘Merlin’ and ‘Merlin Blue Morn’ (blue, lavender, mauve, pink, purple edging fading into a white or near white centre); and ‘Ensign Series’ (more solid colours and very free-flowering) produce somewhat smaller flowers on a more compact plant than the largest Grandiflora hybrids. They are very free-flowering and more weather resistant. All these intermediate Grandiflora hybrids tend to be more often successful when planted in: large beds; broad borders; amongst taller Annuals, Perennials and low shrubbery; landscape planters or larger containers; or when used as an effective groundcovers and as cascades on sloping land or terraces.
‘Super Cascade Series’ contains a remarkable colour range in both double and single forms as well as picotee edges hybrids. These can trail to 3ft/1m or more and flower prolifically over a long period. Flowers are very large open discs and are often fragrant, especially at night. There is a full colour range, especially of solid coloured forms. Some of these, especially the white varieties produce some of the largest and most fragrant blooms of all Petunias.
‘Superbisima Series’ produce immense blooms 5-7in/ 10-17cm across on 12in/30cm pendulous, sprawling, and/or trailing plants. Flower colours are exceptional and include almost every colour. They are especially famous for their picotee, ruffled and exquisitely veined vivid blooms with a delightful perfume. Plants demand heat and sun plus very dry conditions if they are to be successfully grown out in the open. They are excellent in arid and dry climates or in glasshouse situations or can be successfully grown in larger baskets or containers beneath the eaves of a very sunny porch or shelter.
‘Titan Series’ is the largest and most spectacular of the giant Grandiflora Petunias. Plants are well behaved but sprawling growing to 6-8inches/15-20cm tall but can sometimes spread 1m/3.34ft or more. They take 11 weeks to flower from seed and then are covered with immense up to 17cm/7inch flat, open blooms, sometimes with wavy margins. Usually these appear in the traditional solid colours and some are highly perfumed especially in the evening. These are a connoisseur series which need plenty of heat, sunlight and quite dry conditions. They are decimated by hail or heavy rain and do not stand up well against cold, rainy weather.
‘Ultra Series’ cascading Petunias are sometimes sold as ‘Color Parade’ have the widest variety of colours and forms including doubles, semi-double and single forms in a full range of colour; plus many bi-coloured hybrids featuring a central star of white against a contrasting shade or a variety of veined bi and tricolored patterns. These make remarkable basket and especially good bedding plants and are often used in large planter, tubs and as cascades over terrace walls or sloping sites. Their blooms are easily damaged by rain or strong winds. But in a sheltered environment these are unrivaled flowers of remarkable beauty.
‘Victorious Doubles’ are a remarkable group of hardy hybrids. They are fast-growing and robust; sometimes almost rank as they climb and sprawl to cover up to 2ft/60cm or more in diameter. Flowers are numerous and often perfumed in a wide range of bi and solid colour shadings. Flowers can be semi-double to fully double round globes that sometimes resemble large Carnations or small Peony blooms. They are excellent for picking.
‘Pirouette Series’ are nearly edible immense fully double, fragrant blooms that resemble large Carnations or double Peonies. Plants are robust and spreading or pendulous and very free-flowering. These come in a full colour range and include some remarkable picotee forms usually a solid colour with a clear white edging.
Hedgiflora Petunias or ‘Ground Cover’ Petunias feature smaller blooms with better substance so greater weather tolerance. These are robust and spreading plants that can easily cover 1-1.5m/3-5ft across. Most remain rather short at 6-8in/15-20cm or somewhat taller in partial light. They respond well to extra feeding and watering making them ideal for large baskets, planters and tubs, terrace walls and as a spreading groundcover in dry and open areas or as a bedding plant. They are much more tolerant of cold or cool weather, and damper conditions making them ideal for marginal temperate climates.
The popular ‘Color Wave’ series are the best known of this type. ‘Purple Wave’ was the first commercially introduced cultivar hybrid of this spreading Petunia hybrid; growing only 4-6 in/10-15cm tall. The ‘Tidal Wave’ series is taller 16-24in/40-60cm. These spectacular plants are smothered with blooms for much of the season and can easily trail 3-6ft/1-2m from a basket, planter or terrace wall. Now this fabulous series of Petunias are available in a wide range of colours.
Petunia integrifolia, actually the improved ‘wild’ Petunia sometimes sold as 'Surfinia' Petunias, feature a variety of single lavender to purple flower on hardy quickly spreading plants that remain perennial in frost-free climates. These can easily be started from cuttings taken Spring and Summer or wintered-over in the glasshouse. The ‘Opera Supreme’ series of cultivars feature larger blooms in a greater colour range on taller plants that are almost sub shrubs.
Multiflora Petunias sometimes known as ‘Bedding’ or ‘Carpet’ Petunias are bushy, and either compact (12in/30cm or less) or intermediate (18-24in/45-60cm) tall. Usually they are all together bushier but smaller plants with blooms 2-3in/5-7.5cm across in a very wide colour range of double, single or bi colour and veined or wavy-edged forms. The plants are easily raised from seed and spread rapidly, flowering quite quickly and continuously. Flowers are quite weather-resistant and plants are durable to extremes of sunlight as well as heavy rain and cooler and cloudy conditions. They are ideal for bedding and containers of almost any size and are ideal for compact baskets where they will neatly spill over the edges in a semi-trailing habit. The plants are long-flowering and often cover the foliage in blooms.
The popular ‘Carpet’ Petunia and “Madness’ series of Petunia often seen in commercial and street plantings are all Multiflora Petunias. The ‘Neptune Series’ focus on pastel ‘ocean’ shades some with lovely veining and pastels flushes. Plants are very compact and dwarf. Hybrid ‘Star Series’ is another very dwarf hybrid with spectacular vivid blue, mauve, magenta and deep pink discs and a central white star. The ‘Primetime Series’ are amongst the finest and most reliable Multiflora Petunias in all the classic colours and many picotee shades and star/striped patterns. These are all very weather resistant plants.
Floribunda Petunias are a fairly recent addition in the intermediate range. They are highly floriferous, often blanketing the entire spreading plants in colour. Flowers are usually about 3in/7.5cm across in a wide range of colours and many picotee and star/stripe patterns. The ‘Celebrity Series’ of Floribunda Petunias are the best known performers. ‘Dwarf Ensign’ which is nearly identical to its larger grandiflora relative, is one of the hardiest and most prolific of the bedding Petunias.
Flowers are sometimes softly fragrant and plants are well behaved and compact. These are superb garden performers ideal in a variety of climates and highly weather-resistant.
Milliflora Petunias are true miniature Petunias: the Fairy Pixies of the Petunia world. Plants are all together smaller in habit of growth and leaf form as well as flower size: 1-2 in/ 2.5-5cm. in diameter. They are sometimes confused for Calibrachoa but differ in that they all demonstrate the classic Petunia trumpet shape and circular disc flower shape often with pleating producing a fluted appearance. Other hybrids produce nearly flat and open flowers identical to their larger relations in colours and forms but just on smaller plants. These are very hardy and weather resistant, making them very useful for baskets, bedding and all sorts of containers, especially window boxes. They make a wonderful compact companion plant for garden edging and mix well with Alyssum and Lobelia plus a variety of other annual and perennial specie.
'Fantasy Series' (lilac, mauve, pink, purple and reds) and 'Supertunia Mini Series' (wider colour range of blue, lilac, mauve, pink, purple, white and multi-tones) are amongst the most commonly available of these very pretty hybrids. They are delicate in appearance yet quite hardy and reliable.
Species Petunias include all the naturally occurring ‘wild’ species that have been discovered so far. Almost all of these are from South American origin. These are presently being cross and inter-bred to create exciting and much hardier new hybrid species. Most are of little consequence to the home Gardener and often very difficult to obtain outside their native region. But for those living in arid milder climatic regions, these wild flower species are invaluable.
Species Petunias discovered so far include: P. alpicola, P. altiplana, P. axillaris, P. bajeensis, P. bonjardinensis, P. exserta, P. guarapuavensis, P. helianthemoides, P. humifusa, P. inflata, P. integrifolia, P. interior, P. ledifolia, P. littoralis, P. mantiqueirensis, P. occidentalis, P. parviflora, P. patagonica, P. pubescens, P. reitzii, P. riograndensis, P. saxicola, P. scheideana, P. variabilis, P. villadiana. Also included here is Nothospecies P. × atkinsiana (the improved ‘common’ garden Petunia often grown in traditional cottage gardens in an early time).
Petunias hybrids and improved species come in nearly every colour of the rainbow. They are available in fully double forms that closely resemble large Carnation flowers and sometimes double giant globes. There are multitudes of single forms from very miniature and petite babies to blousy and extravagant giants. These are the ideal ‘pretty’ Summer flower for almost any sunny and warm bed, border or container, especially in drier climates.
The relatively new Colour Wave varieties are indeed an exciting new dimension to the future of Petunias. The Colour Wave series are much stronger perennials that can spread into a dense l.5m mat in only a few months and flower at least lightly from Spring until nearly Winter (6-9 months) non-stop in sunny sites. When in full bloom their vivid flowers completely cover the plants! These make great cascading basket and tub specimens as well as effective groundcovers, especially in sloping and sunny sites. The ‘Wave’ series greatly expands the potential climate range of Petunias.
From their humble wild beginnings to what they have become today, pretty Petunias have earned their place in almost every Summer garden. With each new gardening season, more and more wonderful new hybrids are being created by crossing the hardy wild species with existing hybrid cultivars. There is no doubt that Petunias are rising stars in the modern gardening world. This more or less assures that pretty Petunias will become an even more important flower in this new Millennium.
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