One of the most popular annuals, petunias add mountains of color to garden beds and containers. These tough plants are capable of producing loads of blooms all season long and come in a wide variety of colors and patterns. Most petunias available nowadays are hybrids. New varieties come out every year in novel shades and patterns. Countless color options are available, along with patterns like stripes, splashes, and even hearts. The blossom size selection is quite diverse as well. 

Whether you're looking for a low-growing groundcover, a mounding type for containers, or a rambling wild plant to fill up some space, there is a petunia for every situation.

Where to Plant Petunias

Whether you plant petunias in garden beds or pots, they should get a minimum of 6 to 8 hours of direct sunlight per day. Pick a location where the soil is well-drained, with a pH in the neutral to slightly acidic range (6.0 to 7.0).

For the best visual effect, plant petunias in closely spaced groups or drifts. Trailing petunias look best when spilling over walls or containers and hanging baskets. Wherever you plant petunias in the landscape, make sure that they don’t get shaded too much by other plants, and keep in mind that they grow taller as the season progresses.

How and When to Plant Petunias 

Petunias can be planted when the soil has warmed to at least 60 degrees F and there is no more danger of spring frost. Loosen up the soil in the planting area and dig a hole at least twice the size of the root ball for each plant. Place it in the hole and backfill with a mixture of soil and compost. Gently tamp down the soil around the base and water the plants immediately. 

The spacing depends on the variety and location. Multiflora and grandiflora petunias should be spaced about 12 inches apart when planted in full sunlight and a couple of inches less when planted in partial shade. Trailing petunias should be spaced at least 18 inches apart. The compact milliflora petunias can be planted much denser, about 4 to 6 inches apart.

Petunia Care Tips

Light

It is important to plant petunias in full sun. Partial shade, especially in the hot afternoon hours, is acceptable in warm climates but too much shade can lead to fewer blooms and lanky plants. In shady locations, the soil also stays wet longer after a rainfall, increasing the likelihood of rot.

Soil and Water

Petunias are unfussy in terms of soil as long as they are planted in well-drained soils. Poor drainage, however, can lead to rot and fungal issues.

Petunias do not need lots of water, with two major exceptions: potted petunias and trailing petunias need frequent watering. In the absence of rain, in-ground petunias should be watered about once a week, more often during a heat wave. Container plants need daily watering. Petunias in hanging baskets might even need to be watered twice daily in hot summer weather.

Temperature and Humidity

Petunias are heat-loving plants. Hot weather is not a problem for them but they don’t handle high humidity well, so they are not the best choice for locations where summers are hot and humid.

Fertilizer

Because petunias are such vigorous bloomers, they need a substantial amount of nutrients to keep up their blooming power. Plant them in soils rich in organic matter and fertilize them regularly throughout the growing season with a balanced complete fertilizer.

Pruning

Petunias are fairly low maintenance, but many older varieties may require deadheading to keep up a constant display of blooms. Meanwhile, most new types are self-cleaning, so deadheading is unnecessary.

If they get too leggy, some petunias may also benefit from an occasional shearing back to help encourage a new flush of compact growth.

Potting and Repotting

Plant petunias in pots filled with well-draining potting mix and large drainage holes. Unglazed ceramic and terra-cotta pots are ideal because they let excess moisture evaporate. Potted petunias can be planted more densely than petunias in garden beds, depending on the variety, you can fit up to 3 plants in a 12-inch pot. They will need more regular watering than petunias growing in the ground. Repotting is usually not necessary as petunias conclude their life cycle with the first fall frosts.

Pests and Problems

Similar to flowering tobaccos, a close relative, petunias can attract some pesky bugs, especially during the heat of the summer, but rarely in large enough quantities to be of concern. Keep an eye out for whiteflies and aphids, as they are the most likely to show up.

Planting petunias in locations with poorly draining, wet soils, especially in partial shade, can make plants more susceptible to fungal diseases.

How to Propagate Petunias

Most petunias are hybrids that do not come true from seed. Some nurseries offer petunia seeds though the selection is much more limited than when buying plants.

Start the seeds indoors 8 to 10 weeks before the last frost in your area, in pots or seed trays filled with soilless potting mix. The seeds need light to germinate so do not cover them. Keep them evenly moist. At temperatures between 75 to 80 degrees F, the seeds should germinate in 7 to 14 days.

Harden off the seedlings before planting them outside after the last spring frost when the soil has warmed to at least 60 degrees F.

You can propagate petunias from cuttings taken from non-patented varieties, so if you break a stem from your plant, you can grow a new plant. Here's how:

Remove a cutting about 6 inches long and strip all flowers and all leaves except the top pair. Place the cutting in a pot filled with moistened potting mix and firm it around the cutting. Place in bright, indirect light and keep the potting medium moist. After 2 to 3 weeks, your cutting should begin to show new growth.