The Petunia

It's hard to believe that the lavish diversity in today's petunias originated mainly in two species discovered in South America in the mid 1700s and early 1800s. Neither the white-flowered Petunia axillaris nor the purple P. violacea were exactly spectacular specimens. But in breeders' artful hands the petunia has evolved into a group of plants offering many exciting colors in flowers large and small, single and double. Very recent innovations have added two entirely new types to the petunia portfolio.

Petunias are members of the nightshade (Solanaceae) family, which includes tomato, potato, peppers, eggplant, Nicotiana (flowering tobacco), Schizanthus (butterfly flower, poor man's orchid), Datura (angel's trumpet), and Salpiglossis. This last flower, a Chilean annual known also as painted tongue, bears small, widely funnel-shaped flowers that closely resemble the earliest petunias grown in gardens.

For gardeners just beginning to learn their way around petunias, and as a refresher for the experienced flower gardener, here's an overview of the different styles, or classes of petunia and their best uses.

GRANDIFLORA means large-flowered. For its bloom size and glamor, this is the most popular kind of petunia. Double-flowered grandiflora petunias are especially splashy. Double Glorious Mix is a longstanding popular blend for garden beds, window boxes and patio tubs. Among the single-flowered grandiflora petunias are those with richly veined flowers (Daddy Series) and others with white edges (Frost and Hulahoop Series). The Supercascade petunias are single-flowered grandifloras designed for hanging baskets and containers.

Supercascade Lilac Grandiflora

Heavenly Lavender, Multiflora double petunia MULTIFLORA means many flowers. Multiflora petunias generally produce smaller flowers in greater abundance than the grandifloras. The plants and blooms have a better resilience in the face of intense heat, rain and wind compared to the grandifloras. Single multiflora petunias make a grand display in massed garden plantings. The doubles are especially showy in window boxes and containers. Some catalogues separate out certain of the larger-flowered multiflora petunias and list them as FLORIBUNDAS. Stokes, for instance, lists the Primetime Series as Floribundas, which combine the large flower size of the grandiflora with the floriferous resilience of the multiflora.

MILLIFLORA is an entirely new class of petunia, introduced a couple of years ago under the name Fantasy. These "thousand-flowered" petunias are miniatures that form eight-inch (20-cm) mounds of almost solid bloom that are especially effective in containers. Fantasy is available in a color mixture and individual colors.
Fantasy Pink Morn

Pink Wave
Purple Wave SPREADING petunias represent another wholly new class, introduced in 1995 in Purple Wave and now joined by Pink Wave. These are low-growing plants that send out long flower-laden stems. The plants are highly useful as summer ground covers and as trailing plants in hanging baskets and window boxes.

There are other trailing petunias that are not seed-grown but are propagated from cuttings. They are commonly available at garden centres in the spring and are sold in several colors, under the name Surfinia. My favorite is the sweet-scented blue-veined Surfinia, which formed a solid wall of fragrant flowers in baskets hung in front of my potting bench last summer. The plants bloomed all summer and autumn until hard frost, with no care except watering. petunia
Blue-veined Surfinia - Petunia ascillaris hybrid

Seeding
Garden centres offer seed-grown petunia transplants in abundant variety in the spring. But if you'd like to try your hand at growing some of your petunia transplants from seed, it's not difficult to do. Modern petunias germinate easily and grow rapidly. An early March sowing gives plenty of time for the plants to develop into fine young specimens for transplanting in the warmth of May. If you are growing both single-flowered and double-flowered petunias, seed the doubles first.

Petunias can be seeded indoors in March for transplants to set out in May.
Though petunia seeds are small, they are not especially difficult to grow into fine transplants. Be sure to use a sterile seeding mix. I add purchased, sterilized soil to beef up the seeding mix for sustaining the plants from seed to transplanting size in one container, plus a little perlite for enhanced aeration and drainage. If you prefer to transplant the seedlings into individual pots or communal flats when they have developed two sets of petunia-like leaves, the seeding mix alone is enough to start with.
To distribute the small seeds evenly over the surface of the dampened mix, pour the seeds into the dry palm of one hand and take out pinches of the seed to distribute between thumb and forefinger. Drift a very scant amount of the mix over the seeds, press down gently to bring the seeds into intimate contact with the soil, and spray-mist the surface to moisten it.
Give the flat a clear plastic cover and place it in a warm, bright location or under grow lights. Light enhances germination in petunia seeds. Expect germination in 10 to 14 days. With germination, move the plants to a cool, bright spot. The stockiest transplants are produced in cool temperatures around 15 C. and bright light, in a soil kept just modestly dampened.
Wait until the weather is warm in late April or during May to transplant outdoors. Consider using compact multiflora petunias to edge a sunny perennial border or a bed of annual flowers. Petunias are useful for covering the soil at the base of sweet pea vines with color.
Hanging baskets and patio tubs can be planted earlier if a bright, sheltered area is available for holding the containers until it's warm enough to place them out in the open. Hanging basket petunias combine wonderfully with geraniums.

Seed award winner
Though it didn't give such an extended season of bloom, the other flower among the 1998 AAS winners brought to the garden a color I find particularly delightful.
Petunia 'Prism Sunshine' tumbled on 20-inch (50-cm) stems from a planter on the front fence and a windowbox on the south side of the house, its large, creamy primrose yellow flowers like splashes of soft sunlight against dark green foliage. 'Prism Sunshine' is a single grandiflora petunia, a classic beauty that also won a Fleuroselect award.

Prism Sunshine

Stretching
Question: Last year I grew petunias from seed for the first time, with great success except that by the time I came to transplant them the young plants had sent out long stems. Did I do something wrong, and is there a way to prevent this premature stretching? The same thing happened to the plants when it became hot in the summer.
Helen says: If it's any consolation, my petunia transplants often start stretching before I get around to planting them into baskets, planters and garden beds. Unlike professional growers, who are set up with ideal transplant-making conditions and can give full-time care to the plants, most of us home gardeners operate in a more makeshift fashion.
The almost inevitable stem stretching in petunias is not a serious problem. When I come to plant a flat of long-stemmed petunias I simply cut back the stems, making the cuts immediately above a healthy-looking leaf. The plants may look a bit truncated for a brief time, but petunias grow fast to cover the pruning. And the cutting back helps to induce extra bushiness.
Ideally, petunias should be pinched back in the flats as stems begin to lengthen. Pinching simply involves using thumb and forefinger to snip away the growing tip of a stem. Pinching produces a well-branched, compact transplant.
Heat and low light conditions both induce stem stretching. Temperatures around 15 C. or even a little cooler, together with full light, produce the stockiest plants. Making sure the transplants are not crowded helps too. And avoid overwatering, which can cause a certain lankiness in the plants.
In hot summer weather petunias often repeat this stretching routine. It's not uncommon to see long stems bereft of bloom except at the tips. This is a signal to cut the stems back severely, again above a healthy looking leaf close to the base of the plant. Water with fish fertilizer, mulch with compost, then stand back and watch the plants produce masses of new flowering growth.
Where the petunias are on very prominent display, I relay prune to retain some flowers at all times. I do this, for example, on the tiered planting of Supercascade Lilac petunias against the south-facing house wall. They grow in three long planters on shelving to form a solid curtain of greenery and big, single lilac flowers against the wall. When the plants begin to look bare-stemmed, I cut back half the stems and wait 10 days or so to cut back the rest.