How to Grow and Care for Petunias, a Low-Maintenance Annual That Blooms All Summer Long

Petunias come in a full spectrum of colors and shapes, making these unfussy blooms a popular choice for summer containers and garden beds. What's more, petunias are pollinator-friendly and grow quickly; once their seeds germinate, you can expect to see full-size plants in just 12 weeks. With adequate sunlight and well-draining soil, petunias can bloom from spring until fall, providing you with multiple seasons of interest. To ensure this annual flower thrives in your garden, we spoke to experts who explain how to grow and care for petunias.

How to Plant Petunias

You can either plant petunias from seed or from container.

From Seed

To grow petunias from seed, start at least 10 to 12 weeks before your last spring frost, says Eric Groft, CEO and director of Ovsla.

1. Spread seeds on top of a moist-starting mix; avoid submerging them in soil.
2. Cover your container with a clear lid to keep seedlings warm.
3. Keep the soil moist and provide bright light.
4. Once the seeds germinate, remove the plastic cover.
5. Once you see one to two sets of true leaves, harden them off and transplant outdoors.

Mature Plants

Plant container-grown petunias outdoors after the threat of frost has passed, says Carrie Spoonemore, co-creator of Park Seed’s From Seed to Spoon app.

1. Choose a sunny location with well-drained soil.
2. Dig a hole twice as wide as the container and at the same depth.
3. Gently remove the plant from the container, loosen the root ball, and place it in the hole.
4. Space plants 12 to 18 inches apart, depending on the variety and tag instructions.
5. Water thoroughly after planting and keep the soil consistently moist.

How to Care for Petunias

Petunias are easy to care for, but there are some things to keep in mind to ensure they thrive in your garden.

Light

Petunias require a minimum of six hours of direct sunlight per day. But there are varieties that can thrive with some shade, which is beneficial during the peak of summer when UV rays are strong.

Water

Water petunias regularly so the soil is moist but not waterlogged. About 1 to 2 inches of water (including rainfall) a week is sufficient. Note that plants growing in containers may require more supplemental water, says Groft.

Soil

Petunias need well-draining soil that is rich in organic matter, says Spoonemore. These plants won't survive in soggy soil, which may lead to root rot.

Fertilization

Feed petunias with a balanced liquid fertilizer at the time of planting. Once established, use a balanced, water-soluble fertilizer designed for flowering plants every two to three weeks during the growing season, says Spoonemore.

How to Prune Petunias

Pruning petunias helps maintain their shape, encourages bushier growth, and promotes continuous blooming, says Spoonemore. To prune petunias, simply pinch off faded flowers and their stems regularly to encourage continuous blooming. You can also trim back long stems using clean, sharp scissors to maintain a compact shape and remove any damaged or dead growth as needed. "Prune in the morning or late afternoon to reduce stress on the plants," says Spoonemore.

How to Propagate Petunias

You can propagate petunias by seed or by stem cuttings. To do so by seed, simply collect seeds from mature plants and plant them indoors 10 to 12 weeks before the last frost.

To propagate from cuttings, take 4- to 6-inch cuttings from healthy stems and remove lower leaves. Dip the cut-end of the step in rooting hormone, and plant in a moist potting mix. Place cuttings in a warm, bright location out of direct sunlight, says Spoonemore.

Types of Petunias

Petunias have been around since the 19th century and are one of the most popular flowering plants in every nursery. They fall into six main categories, nearly all of which come in a myriad of patterns and colorways and can be grown as annuals in most zones. Petunias might thrive as perennials in more temperate regions, including zones 9 through 11.

Spreading

As the name indicates, spreading or wave petunia plants can reach up to 4 feet; they bloom profusely, making them an exceptional ground cover option. Fairly drought-tolerant, spreading petunias also boast long-lasting blossoms, so long as you nourish them with a water-soluble fertilizer every two weeks (and give them at least six hours of sunlight daily).

Multiflora

A more compact iteration, multiflora petunias work extremely well in windy climates due to their strong stems. But this variety also tends to produce the tiniest blooms. A few common types of multiflora petunias include mirage, primetime, and carpet. The best part? Multiflora varieties require virtually no deadheading. Thanks to their "self-cleaning" abilities, their flowers fall off automatically when spent.

Supertunia

Larger than wave species, supertunia varieties like to spill or spread out (which makes them winners in containers or baskets). This hybrid makes growing and caring for petunias even easier; like multifloras, they do not require deadheading and bloom all season long.

Grandiflora

Although grandiflora petunias produce fewer blooms than other varieties, each bloom grows quite large, ranging between 3 to 5 inches in diameter. These petunias do require deadheading and will not flourish in extreme weather conditions like hard rain, humidity, and high heat.

Cascadia

Another aptly-named iteration, these bright, bold, trailing petunias, which often have crisp white edges, cascade beautifully over baskets, planters, and window boxes—but they work in the ground, too. They thrive in full sun and require moderately moist soil.

Surfinia

These petunias are defined by their bell-shaped blossoms and are most often used as draping plants—they look lovely tumbling over a railing or basket. They grow up to 20 inches tall and prefer full or partial sun and nutrient-rich soil. Expect to see blooms from spring through late fall.

Growing Petunias in Containers

Petunias are a popular container plant and can be grown in window boxes, hanging planters, and more. To do so, use a pot that is large enough to accommodate the plants and allows for proper growth and airflow. "Ensure the container has drainage holes to prevent water-logging," says Spoonemore. "Move containers to a sheltered location during heavy rain or extreme heat to protect the plants."

How to Get Petunias to Bloom

To encourage your petunias to bloom, deadhead regularly by pinching off spent flowers and their stems. "This prevents seed formation and encourages the plant to produce more blooms," says Spoonemore. Additionally, it's essential to ensure the care needs of your petunia plants are being met. Provide petunias with adequate sunlight, well-draining soil, and regular fertilizer and they should bloom until fall.

Common Issues With Petunias

Petunias are generally issue-free, but there are some problems you may encounter when growing this annual.

Rots and Blight

A few common diseases that can overwhelm petunias include stem, crown, and root rot, which all occur due to poor drainage (and over-watering). Botrytis blight can also occur, which may cause discoloration of your petunia leaves and flowers—another condition caused by excess watering. In these cases, it's best to prune any infected sections and dry your bed out to prevent re-infestation, Groft says.

Powdery Mildew

Powdery mildew is also a common disease that may affect your petunia plants. This type of mildew forms when plants are spaced too tightly together and lack proper airflow. To spot this mildew, look for powdery white-colored spores spread out on your leaves and flowers. Neem oil can help, but correcting the plant's spatial conditions is equally as important.

Sagging Blooms

If you notice any sagging petunias, the cause is usually due to insufficient water reaching its roots. Inadequate watering can also cause root binding. If this occurs, cut your plants back by half their height, encouraging new, healthier growth.