What's not to like about petunias? These incredibly versatile plants come in an abundance of sensationally bold colors, are widely adaptable, vigorous, self-reliant and largely pest and disease free. They are low maintenance and drought tolerant, widely available, are a great value, sport a variety of forms and colors, and some even exhibit a light, sweet fragrance. Additionally, these fail-proof, tried-and-true beauties are easy to grow, bloom ceaselessly from late spring to fall and settle in comfortably whether planted in gardens, trailing from containers or spilling out of hanging baskets. They're beautiful, desirable and completely irresistible to butterflies, hummingbirds and gardeners alike. Thanks to new, fashionable shapes and attractively colored blossoms, the petunia is still one of the most popular summer flowers. In short, the perfect go-to gardening friend for sunny places.
History - Then
Though generally treated as annuals by most gardeners, technically they are tender perennials and are members of the potato family of plants. Today's feisty hybrids are the descendants of two lanky, tiny-flowered South American species: the buff-white flowered Petunia axillaries and the night-fragrant, lavender to purple-flowered Petunia violacea. First discovered in South America in the late 1700's these wild varieties quickly captured the imaginations of European breeders who began crossing them in search of the perfect petunia - a plant with large beautiful flowers in a variety of colors.
Following the end of World War II, the transformation in the quality of petunias came with the development of the F1 hybrids. Weddle, one of the founders of PanAmerican Seed Company, won an AAS award in 1949 for the first F1 single-flowered multiflora, 'Silver Medal' and in 1952 crossing a grandiflora with a multiflora producing a F1 vigorous grandiflora hybrid 'Ballerina.'
History - Now
A whole new world opened for petunias and their breeders with the development of the F1 hybrids. This made it possible to regulate their growth from the open, floppy forms to a bushier type with better weather resistance, an increasing range of colors and color-combinations and a far superior ability to weather the rigors of summer.
As is quite obvious, in recent years the world of petunias has become a complex world, for there are - literally - hundreds of named petunia varieties. But a bit of advice for pairing the right petunia with your gardening needs can be summarized, in part, in the following manner.
Grandiflora: large-flowered blossoms (4-5") consisting of both single- and double-flowering cultivars form mounds of colorful solid, striped, deeply veined, variegated or edged in a contrasting shade called picotee. Grandifloras prefer a cool, dry sunny environment in protected areas and dislike hot, wet or windy conditions, and work well in both containers and beds.
Multiflora: compact plants with smaller (1.5-2") flowers than the grandifloras; however, they bloom prolifically and freely all season long. These plants have single or double flowers and are available in a rainbow of colors, often with contrasting centers or stripes. Bred primarily for the wetter climates these petunias perform admirably in adverse weather conditions especially during very hot or very wet spells.
Milliflora: petite, (1-1½") blossoms produced with wild abundance that cover the plant with beautiful vibrant colors. Perfectly suited to containers, hanging baskets, miniature gardens and as edging plants, these delicate beauties bloom earlier, do not stretch, add fullness and contrast of size and color when combined with larger blooming plants.
Spreading: low-growing plants only (4-6") in height that can spread up to 5 feet across. These are fast growing plants with excellent heat and drought tolerance, require very little maintenance, and make excellent flowering ground covers. Their greatest popularity lies in their wild profusion of blooms that tumble out of hanging baskets, window-boxes and tall containers from late spring well into late fall in milder and warmer regions.
Hedgiflora - one segment of Spreading: have growth habits based on how closely the plants are spaced in the garden. Grown close together, they form a dense, mounded hedge from 16 to 22 inches tall. Grown in restricted space with some support, they act like vines growing upward an extra 2 to 3 feet. But when given plenty of space to roam, they make a floriferous groundcover spreading 2½ to 3 feet.
Floribunda: an improved multiflora petunia bred to have larger single- and double-flowered varieties that bloom earlier while producing an abundance of flowers. Like the grandifloras, they flower earlier, yet tolerate both hot and wet periods, perking up quickly after every rain shower. Floribundas are a fantastic selection for mass plantings in the landscape, and for container plantings in pots and hanging baskets.
Petchoa (SuperCal): a combination of the best characteristics of the petunia and calibrachoa plants. The Petchoa 'SuperCal' plants deliver unique colors, sturdy blossoms and non-sticky foliage to overflowing hanging baskets.
For growing and planting instructions, read the full Petunia Fact Sheet here. Petunia Maintenance
Petunias don't require a lot of care, but they do benefit from some attention. During dry weather, a deep watering once a week should be sufficient for petunias in beds and borders. Plants in containers, hanging baskets and window boxes will need to be watered when the soil surface becomes dry - on extremely hot, sunny days that could be daily - and fertilized every couple of weeks with a dilute fertilizer solution.
Always check the cultural tags that come with the purchase of your plants. Many of the new cultivars are bred for compactness or mounding and require no pinching back or deadheading. Your cultural tags will give you this information. But as a general rule, to encourage additional blooms and improve plant appearance, remove the spent flowers on grandiflora and double petunias. This not only keeps plants blooming longer, it also keeps plants looking fresh, healthy and well groomed. The smaller flowering types, such as the milliflora and spreading petunias are self-cleaning and don't require deadheading. And although it isn't practical to deadhead sweeping stands of petunias in the garden, it's advisable to do so for plants in containers. After pruning, fertilize and water the plants to promote new growth.
Problems:
Today's newer cultivars are pretty much disease-resistant, but as with all plants, a few problems can develop and you will want to deal with them as soon as possible.
Newly germinated seedlings can fall prey to damping off, a fungus that attacks at the soil level and is irreversible. The young seedlings will wilt and die almost overnight. Avoid damping off by using a commercially available soilless mix and use only clean, sterilized containers for starting seeds.
Young plants are susceptible to Botrytis, a fungus that is also soil-borne and spreads quickly from an infected plant to a healthy one. It thrives in cool, moist conditions, forming a powdery mold on stems, leaves and flowers. Watering only early in the morning, avoiding overhead irrigation and keeping plants spaced for good air circulation are all good ways to avoid these problems.
Petunias are also susceptible to various viruses which can leave foliage stunted and deformed with discolored and deformed flowers. The safest control is to remove and destroy diseased plants and keep aphids and other insects which can transmit the disease off the plants by hosing the plant with a strong blast of water.
Petunias in the landscape can be bothered by different pests: flea beetles which eat holes in the leaves of the plants and the small, green budworm caterpillar which attacks plants in late June and July and feeds on the flower buds. Usually, you won't see the actual caterpillar, but you should notice small black droppings and tiny holes in leaves. If you have a major infestation, apply Bt (Bacillus thuringiensis).
Petunia plants may look limp and scraggly after a hard rain; however, the newer cultivars usually perk up within hours. Most petunias have naturally sticky leaves and stems (some of the newer cultivars have this trait bred out of them), so don't panic and think this condition is disease or pest related.
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The National Garden Bureau recognizes and thanks Betty Earl as author of this fact sheet. The petunia fact sheet is provided as an educational service of the National Garden Bureau. There are no limitations on the use. Please credit the National Garden Bureau.
