Petunia

Petunias are among the most commonly planted annuals because they’re so easy to grow. If you think they’re too old-fashioned, look again. There are many new varieties available in a wide range of colors and forms. Color choice today goes way beyond red, white, and blue. Double, ruffled, striped, upright, or cascading—there’s practically no limit to petunia variety.

Choosing Petunias

There are hundreds of petunia varieties. They fall into four groups based on flower size and growth habit. Some are more suited to containers, while others are better for massing in the garden.

• Grandifloras, the most common type, produce large flowers that are 4 to 5 inches across. They may be singles or doubles. Some have a cascading habit that makes them more suitable for hanging baskets and window boxes. But most are upright plants that develop into mounds of flowers that are twelve to fifteen inches tall. Space them about one foot apart, closer in containers or anywhere you want them to look fuller right from the start.
• Multifloras are often more compact. Their flowers are smaller than the grandifloras, but they tend to grow faster, bloom more freely, and have more weather-resistant petals. Multifloras are also available in single or double forms, though most are singles. Typically, they're massed together to create big splashes of color in the garden. Multifloras can also be spaced about a foot apart.
• Millifloras are compact, miniature plants with tiny 1 to 1 1/2 –inch flowers only an inch to an inch and a half in diameter. They make good edging plants and are also attractive when mixed with other annuals in containers. Milliforas may be spaced as close as four to six inches apart.
• Groundcover types, of which the ‘Wave’ and ‘Surfinia’ series are best known, are only about six inches tall, but spread rapidly. They can cover a large area over one growing season, making them ideal for scrambling down a hillside or planting atop a retaining wall. They're also popular in hanging baskets and window boxes, where they can trail three feet or more over the summer. When grown in full sunlight, they are covered in flowers. But they require regular fertilizing and more frequent watering than other types.

Growing Petunias

Wait until soil warms up and frost danger has passed before planting petunias into the garden. Plants need full sun to part shade—at least five or six hours of sunlight per day. The more sun they get, the more they flower. They prefer well-drained soil. It’s always a good idea to enrich your soil with organic matter such as compost.

Care

Petunias tolerate heat well and don’t require lots of water. Watering thoroughly once a week is usually sufficient, except during times of drought. Soak soil to a depth of six inches every time you water. If possible, water at soil level rather than overhead, which can encourage disease.

Hanging baskets and other containers need more frequent, perhaps daily, watering.

You may incorporate a granular organic fertilizer into the soil at planting time. Otherwise, you can fertilize every couple of weeks with a liquid organic fertilizer that is formulated for blooming plants. If possible, it's a good idea to remove faded flowers, including the portion below each flower where seeds will develop. This encourages more blooms and keeps the plants tidy. If your petunias get scraggly, prune them back by half and they’ll grow back bushier.

Pests and Diseases

Petunias are usually quite pest free. Aphids occasionally attack both young and established plants; knock them off with a spray of water. Rain can damage some plants, particularly grandiflora types. Gray mould can also be troublesome in humid weather. Look for weather-resistant varieties.

Growing Petunias from Seed

Petunias are somewhat difficult to start from seed. You must start them indoors 10 to 12 weeks before you want to plant them outside. Don’t cover the seed; it needs light to germinate. Seedlings start to emerge after 7 to 21 days at 70 to 80 degrees. After seedlings emerge, relocate them to a bright location at about 60 degrees.

Plant out when all danger of frost has passed. Harden off young plants by putting them outside on sunny, warm days. Then bring them back in at night for several days before planting them outdoors permanently.

Good Companions

• Petunias are useful in containers because they’re such profuse bloomers. Combine them with interesting foliage plants such as lotus vine or sweet potato vine.
• Pair trailing varieties with more upright annuals such as angelonia, snapdragons, or celosia.

Other Annuals to Grow

• Impatiens
• Marigolds
• Zinnias
• Morning Glory
• Portulaca