Petunias (Petunia spp.) are one of the most popular garden flowers for both borders and containers. They are prolific bloomers; you can find them in just about every color but true blue; and they have wide, trumpet-shaped flowers and branching foliage that is hairy and somewhat sticky. Within the petunia genus, there is great variety and most are sold as hybrids: single and double blooms; ruffled and smooth petals; striped, veined, and solid colors; mounding and cascading growth habits; and even some with fragrance.
Petunias are fast-growing plants. When started as seeds, they're germinated and ready to be planted outdoors—after the last frost date—in about 12 weeks, reaching full size by late spring.
|Botanical Name||Petunia spp.|
|Mature Size||6–24 in. tall, up to 36 in. wide|
|Sun Exposure||Full sun|
|Soil Type||Well-drained, moist|
|Bloom Time||Spring, summer, fall|
|Flower Color||Pink, purple, yellow, red, orange, green, white|
|Hardiness Zones||10–11 (USDA)|
|Native Area||South America|
The primary blooming season for petunias is in the summer, though they can start in the spring and stretch into fall until the temperature drops and frost arrives. Extreme summer heat also can cause a temporary cease in blooming. Older petunia varieties typically need deadheading (removing spent blooms) for them to continue blooming. Many newer varieties don’t require deadheading, though they’ll still benefit from it to maximize their blooms.
Petunias also will require regular watering and feeding throughout the growing season (spring to fall). And they might appreciate some protection from extreme weather, which can involve moving container plants to a protected area or setting up a temporary cover over garden beds.
Watch Now: How to Care for Planting Petunias in a Hanging Basket
Most petunia varieties prefer full sun, meaning at least six hours of direct sunlight on most days. But in the heat of summer, partial shade (especially from the strong afternoon sun) will help to keep them refreshed and blooming better.
Petunias prefer a light, fertile soil that provides good drainage. They can tolerate a variety of soil types as long as they are well-draining. Plus, they like a slightly acidic soil pH.
Like many flowering annuals, petunias don’t like to be dry for long periods. But they also don’t like to sit in soggy soil, which can rot their roots. Plus, too much water can result in leggy plants with few flowers. In general, it's sufficient to soak beds weekly with 1 to 2 inches of water when you don't have rainfall. However, some spreading varieties and plants grown in containers typically need more frequent and deep watering. Try not to let the soil dry out more than 2 inches down.
Temperature and Humidity
The ideal temperatures for petunias are roughly 60 degrees Fahrenheit to 75 degrees Fahrenheit during the day and 55 degrees Fahrenheit to 65 degrees Fahrenheit at night. They can tolerate temperatures all the way down to about 40 degrees Fahrenheit, but frost and freezing temperatures will damage and ultimately kill the plants. Low to moderate humidity levels are best for these flowers.
Feed petunias at the time of planting with a balanced fertilizer. It’s also helpful to work some compost into the soil. Then, starting in July and continuing until the plants decline in the fall, fertilize every two to three weeks with a liquid fertilizer made for flowering plants. Some of the spreading varieties need weekly fertilization, so be sure to check your plant’s individual care instructions.
Types of Petunias
- 'Blue Spark Cascadia' has trailing violet flowers with a sweet scent.
- 'Supertunia Silver' features white flowers with lavender throats and veins; it's a profuse bloomer with good tolerance for extreme weather.
- 'Prism Sunshine' sports large, buttery yellow flowers, and has good weather tolerance.
When planting young petunias, pinch back the stems to encourage more branching and a fuller plant. How far back to pinch depends on the plant. If it is a short, stocky seedling, just pinch an inch or less. But if the seedling is gangly, you can pinch back the stem by half.
How to Grow Petunias From Seed
It's most common to purchase young petunia plants from a nursery. But it can be worth the challenge to grow petunias from seed, especially if you're trying for a particular variety. Start your seeds at least 10 to 12 weeks before your zone's projected last frost date. Here are the steps for planting petunias from seed:
- Spread the tiny seeds on top of a moist seed-starting mix. Gently press them down, but do not bury them as they need light to germinate.
- Then, cover the container with clear plastic, and put it in a warm spot but out of direct sunlight. You should see seedlings within seven to 10 days.
- Once they emerge, remove the plastic.
- When the seedlings have three true leaves, they can be transplanted into their own pots until they are ready to be transplanted outdoors.
Common Pests & Plant Diseases
Some pests that might bother petunia plants include aphids, flea beetles, slugs, and snails that feed on the stems and leaves. Often you can just hose pests off the plants with a strong blast of water. But if the infestation is severe and impeding flowering, you can use an insecticide.
Petunias can be susceptible to fungal diseases, such as gray mold, especially in rainy climates. Opt for a variety that has a higher tolerance for moisture if you live in wet conditions.
Common Problems With Petunias
Petunias are easy-going plants that bloom often, but they occasionally have issues you can keep under control.
Wilted Flowers or Leaves
There are a number of reasons for wilted petunia flowers or leaves, but most of the reasons come down to water: too much, or too little. Check the soil and if it's not damp, water your petunias. If moist, ease up on your watering routine.
Petunias often develop leggy stems, but it's easy enough to remedy: deadhead flowers regularly by pinching back. If this doesn't help your petunia fill out, you can prune its stems back to 2 to 3 inches long, and as it regrows it will be less leggy.
Are petunias easy to care for?
Petunias are super easy to care for! Give them plenty of sun and regular watering, and they'll reward you with abundant blooms.
Can I grow petunias indoors?
Though it's more typical to grow petunias outdoors since they need lots of sun and water, it is possible to replicate the conditions indoors for these blooms. Just put them on a very sunny sill and keep on top of watering and they may last longer than they would outdoors as annuals. Turn the plants every few days to give them even sun for the best color blooms.
How long do petunias live?
In most climates, petunias last one season as annuals. But, in certain warm climates, petunias will last several seasons.
Pentunia (Group). Missouri Botanical Garden.
Botrytis blight outbreaks expected in greenhouses due to weather. Michigan State University Extension.