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Petunias: How to Plant, Grow, and Care for Petunias | The Old Farmer's Almanac

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Petunias

Photo Credit
Pilat66/Getty Images
Botanical Name
Petunia spp.
Plant Type
Flower
Sun Exposure
Full Sun
Soil pH
Slightly Acidic to Neutral
Bloom Time
Spring
Summer
Fall
Flower Color
Blue
Multicolor
Orange
Pink
Purple
Red
White
Yellow
Hardiness Zone
9
10
11
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How to Plant, Grow, and Care for Petunias

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Pretty petunias are one of the most popular flowers because of their exceptional blooms and long flowering period. As with most annuals, they get leggy by midsummer, so you’ll want to prune the shoots back to about half their length. See how to plant and take care of your petunias to keep them blooming.

About Petunias

Petunias are treated as annuals in most areas, but can be grown as tender perennials in Zones 9 to 11. The flowers come in many colors and patterns, and bloom from spring until frost!

These colorful annuals can really add pop to a front lawn and are often used in borders, containers, hanging baskets or even as a seasonal groundcover. Some even have a slight fragrance. Their height can vary from 6 inches to 18 inches and they can spread along the ground anywhere from 18 inches to 4 feet.

Types of Petunias

Petunias are divided into different groups, mainly based on flower size:

  1. Multiflora petunias are the most durable and prolific. They have smaller but more abundant flowers and are ideal for summer bedding or in a mixed border (because they are more tolerant to wet weather).
  2. Grandiflora petunias have very large flowers and are best grown in containers or hanging baskets (because they are more susceptible to rain damage). These large petunias often do not fare as well in the south because they’re prone to rot during humid, hot summers. 
  3. Floribundas: Floribundas are intermediate between the grandiflora and the multiflora groups. They are free-flowering like the multiflora varieties and produce medium-sized blooms.
  4. Millifloras: Milliflora petunias are much smaller than any other petunias on the market. The flowers are only 1 to 1Âœ inches wide, but they are prolific and last all season!
  5. Spreading or Trailing Petunias: These are low-growing and can spread as much as 3 to 4 feet. They form a beautiful, colorful groundcover because the flowers form along the entire length of each stem. They can be used in window boxes or hanging baskets.

Planting

Petunias need full sun or they will become spindly. They don’t tend to flower well in shade.

The soil should drain well and not stay overly wet, especially in containers. It should also be moderately fertile to promote the best growth. Amend poor soil with finished compost prior to planting.

When to Plant Petunias

  • It’s easiest to buy young plants from a nursery that sells petunias in flats. Look for plants that are short and compact. Leggy petunias with tons of flowers already won’t settle in as fast.
  • If you want to grow petunias from seed, start the seeds indoors 8 to 10 weeks before your last spring frost date. (See your local frost dates.)
  • Plant young petunias outdoors after your last spring frost date, but keep a close eye on the weather forecast and protect young plants from late frosts. 

How to Plant Petunias

  • Petunia seeds are very small (dust-like!) and need lots of light in order to germinate.
  • When the young plants have three leaves, plant them outside.
  • Space the plants about 1 foot apart.
  • If you’re planting petunias in containers, use a container potting mix that will drain well.

Hanging basket of petunia flowers

Growing
  • Petunias are fairly heat tolerant, so you shouldn’t have to worry about watering them frequently. A thorough watering once a week should be sufficient (unless there are prolonged periods of drought in your area). Avoid watering shallowly, as this encourages shallow roots.
    • Note: The spreading types of petunias and those in containers will require more frequent watering than those planted in the ground.
  • Fertilize petunias monthly with a balanced fertilizer to support their rapid growth and heavy blooming. Double-flowered cultivars enjoy a biweekly dose of fertilizer.

What to Do With Leggy Petunias

  • By midsummer, most petunias tend to get leggy, producing blossoms at the tips of long, leafless stems. To keep petunias tidy and flowering, we prune the shoots back to about half their length. This will encourage more branching and more flowers.
  • After pruning, fertilize and water the plants well to force out new growth and flowers. The plants may look raggedy at first but they’ll rebound with more color and blooms.
    • Older garden petunia plants can be pruned prune hard (within a few inches of the base) to re-encourage vigor, especially in cooler climates, but keep the remaining leaves.
  • Remove faded, old, or dead blossoms (a practice called “deadheading”) to both improve blooms and attractiveness, especially for the larger-flowered petunias. Deadheading prevents seed pods from competing with blooms for the plant’s food supplies. Clippings can be added to a compost pile to be recycled.
Recommended Varieties

Multifloras

  • ‘Carpet Series’ is very popular. They are compact, early blooming with 1Âœ-to 2-inch blooms that come in a wide variety of colors, and are ideal for ground cover.
  • ‘Primetime’ series stay compact and uniform, covered with 2ÂŒ-inch flowers.
  • ‘Heavenly Lavender’ is an early, compact, double, deep lavender blue with 3-inch blooms on 12-to 14-inch plants

Grandifloras

  • ‘Sugar Daddy’ (Petunia Daddy Series), which sports purple flowers with dark veins.
  • ‘Rose Star’ (Petunia Ultra Series), whose flowers look striped because of its rose-pink flowers with a white center.

Floribundas

  • ‘Celebrity’ series petunias are compact and rain-tolerant. The flowers reach 2Âœ to 3 inches across.
  • ‘Madness’ series petunias have big, 3-inch flowers in many veined and solid colors. They are compact and bloom until frost. They bounce back well after rain.
  • ‘Double Madness’ petunias are compact and floriferous with big, 3-inch flowers all through the summer. Like their single counterparts, ‘Double Madness’ petunias bounce back within hours of a rainstorm.

Millifloras

  • ‘Fantasy’ forms neat, compact mounds.

Trailing Petunias

  • ‘Purple Wave’ was the first cultivar in the class of spreading petunias. It produces large blooms of deep rose-purple. It is tolerant of summer heat, drought and rain damage. ‘Purple Wave’ remains under 4 inches tall.
  • ‘Wave’ series petunias are available in a multitude of colors. Most are not quite as ground-hugging as the original. They are weather-tolerant, disease resistant and heavy-blooming.
Pests/Diseases

Petunias have few serious insect or disease pests, though aphids and slugs can be an issue. Avoid wetting the foliage and flowers when watering to help prevent disease.

Petunia Pests and Diseases
Pest/Disease Type Symptoms Control/Prevention
Aphids Insect Misshapen/yellow leaves; distorted flowers; leaf drop; sticky “honeydew” (excretion) on leaves; sooty, black mold Knock off with water spray; apply insecticidal soap; inspect new plants carefully; use slow-release fertilizers; avoid excess nitrogen; encourage aphid predators such as lacewings, lady beetles/bugs, spiders
Slugs/snails Mollusk Irregular holes in leaves/flowers; slimy secretion on plants/soil; seedlings “disappear” Handpick; avoid thick bark mulch; use copper plant collars; avoid overhead watering; lay boards on soil in evening, in morning lift and dispose of pests in hot, soapy water; drown in deep container of 1/2 inch of beer or of sugar water and yeast sunk to ground level; apply 1-inch-wide strip of diatomaceous earth around plants
Flowers
Annuals

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Comments

Lillie (not verified)

5 months 4 weeks ago

Earlier this season I found a beautiful Black Petunia and it was just gorgeous! It bloomed and did well for a few weeks and then it just drooped and seems to be dying. I would love to know if there is some way I could revive it.

Your black petunia sounds like it had a great start to the season. Drooping and/or wilting can happen for a variety of reasons, most often with either too much or too little water.

Petunias are rather drought and heat tolerant, and do best with a thorough watering once a week. The key is for good drainage because excessive water in the soil can cause the roots to be affected. They prefer slightly moist soil to dry soil, so check your soil to see where things stand before adding more moisture.

If your plant does not perk up when watered, stop watering it and allow the soil to dry thoroughly. Petunias also benefit from a dose of balanced fertilizer monthly.

Drooping can also be due to a lack of sun, as they prefer full sun, or a sign of insect or fungal issue.

Cindy (not verified)

1 year 6 months ago

I was so relieved to come across Alicia's comment regarding withering petunias. She has described exactly what has happened with my petunias this year!! Exactly!! I have not been able to determine the cause of this problem either. Could there have something in the potting soil used at the greenhouse? I would really like to know the cause so as not to duplicate the problem next year. Nearby flowers don't seem to be negatively affected.

Alicia Alicia McCord (not verified)

1 year 7 months ago

I have successfully grown petunias for many years. I put them in pots on my front steps as well as in the flower beds on either side of the steps, all in full sun. Last year however, they failed miserably. I planted around 60 plants from six-packs over a 3-4 week period. Some died within a week of planting, some after a couple weeks, some after several weeks or even two months. All went through the same stages: one day the plant would look vigorous and healthy; but the next day, the leaves would look wilty - the same look as when water is needed, but water was not needed as the ground was adequately moist; the third day the plant would be withered completely. One by one, the petunias went through these stages until I had only one that made it through most of the summer. This summer, after 4 weeks in the ground, the same thing is happening. I am losing plants daily. I can find no evidence of pests nor of gophers (though gophers would not be able to bother the potted plants). I have kept the soil moist but not wet. I thought that perhaps there was something wrong with my soil, but the petunias in pots with potting soil were/are dying just the same way as those in the soil. I'm completely baffled. As I said, I have successfully grown petunias for many years. I will appreciate any insight given. Thank you.

Rox Shinobi (not verified)

2 years 1 month ago

Hello, I had gorgeous “Galaxy Petunias” that were mainly purple in color with speckles of white. This last bloom all the flowers came out fully white with the only purple being in the bottom of the buds (closest to stem). Can anyone tell me why this happened and what I can do to get my flowers back to their prior glory? Thank you in advance.