AMES, Iowa – Petunias are one of the most common annuals in garden centers each spring. Its colorful flowers adorn tubs, hanging baskets and garden beds all summer long. In this article, Iowa State University Extension and Outreach gardeners answer questions about growing petunias in your landscape.
What Types of Petunias Can I Plant in My Garden?
petunia (petunia × hybrida) cultivars can be divided into four main categories or types based on flowering and growth characteristics.
grandiflora have large single or double flowers, up to five inches in diameter, on hilly, trailing plants. Common grandiflora petunias include cultivars in the Dreams, Ultra, Prism, Limbo, Daddy, Supercascade, and Storm series. Overall, grandifloras have large flowers, but not as many flowers as the other species. The buds don’t last as well even in rainy weather or heat. Plants can become unkempt and straggly by late summer.
During multiflora Petunias produce smaller, single or double flowers (1-2 inches in diameter), they are more common than grandifloras. Multifloras also have a hilly, trailing habit but are generally more compact and resilient to wet weather than the grandifloras. They work well in mass plantings, flower beds, and containers. More modern varieties of multiflora petunias are sometimes referred to as floribundas. Multiflora petunias include cultivars in the Celebrity, Carpet, Mirage, Madness, and Hurray series.
milliflora Petunias are compact, miniature plants that produce profuse blooms ranging from 1 to 1½ inches in diameter. They are a good choice for containers and borders of flower beds. Milliflora petunias include cultivars from the Fantasy and Picobella series.
spreading or ground cover Petunias are sturdy, low-growing plants that spread over large areas, sometimes up to 3 or 4 feet in diameter. Spreading petunias have excellent heat and drought tolerance and require little maintenance. They are a great choice for containers and baskets and as annual ground covers. Some varieties of this group are referred to as Hedgiflora types. Spreading Petunias include the Wave, Shock Wave, Easy Wave, Tidal Wave, Ramblin’, Triology, and Avalanche series.
Some popular series of petunias don’t exactly fit into these four groups. They possess some of the best traits of any group. They tend to have large buds with a hilly, pendulous but compact habit and excellent heat and rain tolerance. These include petunias from the Surfinia, Supertunia and Suntunia series.
million bells (Calibrachoa) is a species closely related to the petunia with many small petunia-like flowers and a compact pendulous habit perfect for containers and hanging baskets. Popular Million Bells strains include those in the Superbells, Cruze, and Million Bells series.
What is a good planting spot for petunias?
Petunias thrive best in sunny locations. The planting site should receive at least six hours of direct sun per day. They also require moderately fertile, well-drained soil. Crown or root rot can cause problems in damp, poorly drained sites. Poorly drained soils can often be improved by incorporating organic matter (compost, peat or composted manure) into the soil.
Many petunia varieties are also suitable for containers, window boxes and hanging baskets.
What should I look for when buying petunia plants?
When buying petunias, choose compact, stocky plants. Tall, spindly petunias need pinching to allow the plants to spread and take longer to develop into attractive plants. If you buy plants from a greenhouse, harden the petunias outdoors for a few days before planting them in the garden. First place the plants in a shady, sheltered spot and then gradually expose them to longer periods of direct sun. Bring the plants indoors when freezing temperatures are forecast.
When can petunias be planted outdoors?
Petunias should be planted in the garden after the threat of frost has passed. It’s usually safe to start planting petunias in late April in southern Iowa and mid-May in northern parts of the state.
Plant petunias about 30 cm apart. The propagating types should be planted 2 to 2½ feet apart. Pinch back grandifloras and multifloras to encourage branching. Pinching is especially helpful with tall, leggy plants. Millifloras and sprawling petunias usually don’t need pinching.
How should I care for petunias during the growing season?
In dry weather, a heavy watering every seven to ten days should be sufficient for petunias in beds and borders. Plants in containers need to be watered more often. Check the containers frequently and water when the soil surface becomes dry. Petunias growing in pots should be fertilized every two to four weeks with a diluted fertilizer solution.
To encourage additional blooms and improve the appearance of the plants, remove faded flowers from grandiflora petunias. Milliflora, Spreading and some Multiflora petunias are self-cleaning and do not need to be removed. Leggy petunias can be rejuvenated by cutting them back to about half their length in midsummer. Fertilize and water plants after pruning to encourage new growth.
Shareable photos: 1. Pink Petunias. 2. Petunias in the basket.