By Julie Christensen
Petunias are possibly the most popular flowering annual in the U.S — and what’s not to love about them? They bloom all summer long and have a faintly sweet fragrance that becomes more pronounced in the evening. Petunia flowers come in a huge variety of colors, including variegated and striped varieties. They’re also available in varying sizes, growth patterns and flower forms. Petunias work well as both a bedding plant and in containers and baskets.
The most common type of petunia is the grandiflora petunia, an old-fashioned plant that produces large flowers up to 5 inches across. Some varieties produce ruffled or double flowers. The one drawback to grandifloras is that they tend to become straggly after heavy rains or intense heat. They need continual deadheading and pinching to remain attractive throughout the summer.
Multiflora petunias are similar to grandiflora petunias, but they produce slightly smaller flowers in abundant quantities. They hold up better to the rigors of summer weather and don’t need quite as much maintenance. They also come in single, double and ruffled forms.
Milliflora petunias produce tiny 1 inch blooms. Some varieties have a trailing habit. These petunias are excellent as an accent plant in containers, or use them solely for dramatic effect.
Spreading petunias are your best bet for low-maintenance blooms all summer long. These petunias tolerate drought and heat and can survive without a lot of deadheading. They can spread 3 feet or more in one season, making them an excellent choice as a ground cover. Some have a trailing habit and look beautiful in hanging baskets.
Planting and Caring for Petunias
Petunias need rich, well-draining soil, full sun and warmth. Most gardeners prefer to grow them from nursery transplants, but you can start them from seed, as well. Fill a clean seed starting tray with a loose seed-starting medium. Place the seeds on top of the soil, but don’t cover them with soil. Petunias need light to germinate. Spray the soil lightly with water from a spray bottle to moisten it and cover the tray with plastic wrap. Set the seed tray in a warm place so it stays around 75 to 80 degrees Fahrenheit. Water it frequently to keep the soil moist, but not soggy.
Plant petunias outdoors after the last expected frost when the plants stand at least 3 inches tall and have two or three leaves. If you buy nursery transplants, choose small, compact plants. Tall, leggy plants don’t fare well after transplanting. Amend garden soil with a bit of compost to improve drainage. Use a high-quality potting soil for pots and hanging baskets. Never use garden soil in containers. It’s too heavy and can harbor diseases.
Water petunias at least weekly, and as often as every other day or so during hot weather, to keep the soil slightly moist, but not wet, which can encourage legginess. Remove spent flowers and pinch the plants back occasionally to encourage compact growth. Milliflora and spreading petunias don’t need deadheading – another reason to grow them. Fertilize petunias every three weeks with 1 tablespoon granular all-purpose fertilizer diluted in 1 gallon water. Bring petunias indoors if a frost threatens because they’re not cold hardy.
Potential Pests and Disease Problems
Petunias don’t have many pest or disease problems, but you may encounter budworm caterpillars. These green caterpillars are difficult to see, but you may notice black, seed-like droppings. The caterpillars eat their way through flowers and leaves. Pick them off by hand and destroy them or dust the plants with Bt (bacillus thuringiensis).
Petunia Varieties Worth Trying
- Grandiflora cultivars to try include plants in the EZ Rider, Storm, Supercascade and Dreams Series.
- Try double multifloras for their extravagant blooms. Consider the Hurrah, Celebrity and Carpet Series.
- The most common milliflora petunias include those in the Fantasy or Picobella Series.
- Wave, Easy Wave, Tidal Wave or Avalanche Series are all spreading cultivars.
Want to learn more about growing petunias?
Visit these resources:
Petunia from Colorado State University Extension
Petunias for the Porch, Patio and Garden Spot from the University of Vermont Extension