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Planting and Growing Petunias

Image Credit:
Pilat66/Getty Images
Botanical Name
Petunia spp.
Life Cycle
Tender Perennial
USDA Zones
9a
9b
10a
10b
11a
11b
Toxicity
Non-toxic
Sun Exposure
Full Sun
Water Needs
Moderate
Height
Under 1 foot
Spread
1–3 feet
Soil pH
Acidic
Bloom Time
Spring
Summer
Fall
Flower Color
Blue
Multicolor
Orange
Pink
Purple
Red
White
Yellow
Special Features
Container-Friendly
Attracts Butterflies
Attracts Hummingbirds
Attracts Pollinators
Resilience
Heat-Tolerant
Plant Type
Flowers
Written By: Catherine Boeckmann Executive Digital Editor and Master Gardener
Almanac Guide to Herbs

Pretty petunias are popular because of their exceptionally long flowering period. As with most annuals, they get leggy by midsummer, so you’ll want to prune the shoots back by half. See more tips on planting and caring for petunias to keep them blooming.

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 seasonal ground covers. 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.

pink and white petunias

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. 

Where to Plant Petunias

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.

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

Watering

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.

Fertilizing

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 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.

Pests and Problems

Petunia Problems

Petunias are generally easy to grow and have few serious problems, but poor growing conditions can affect their health and flowering.

If petunias become leggy or produce fewer blooms, they may not be getting enough sunlight. Petunias grow best in full sun and need regular deadheading to encourage continuous flowering.

Overwatering or poor drainage can also cause root problems and weak growth. Petunias prefer consistently moist soil, but they should not sit in soggy conditions.

Petunia Pests

Petunias have few serious insect pests, but aphids and slugs can sometimes cause damage.

Aphids are small insects that gather on stems and buds, sucking plant juices and weakening growth.

Slugs may chew holes in leaves and flowers, especially during damp weather.

To prevent pest problems:

  • Check plants regularly for insects
  • Spray aphids off with water if needed
  • Handpick slugs or use barriers around plants

Petunia Diseases

Disease problems are usually caused by excess moisture and poor airflow.

Fungal diseases can develop if foliage and flowers stay wet for too long, especially in humid weather.

Petunia Pests and Diseases
Pest/DiseaseTypeSymptomsControl/Prevention
AphidsInsectMisshapen/yellow leaves; distorted flowers; leaf drop; sticky “honeydew” (excretion) on leaves; sooty, black moldKnock 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/snailsMolluskIrregular 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

Types

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 multiflora groups. Like the multiflora varieties, they are free-flowering 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 1½ 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. Because the flowers form along the entire length of each stem, they form a beautiful, colorful ground cover. They can be used in window boxes or hanging baskets.

Flowers
About The Author
Catherine Boeckmann

Catherine Boeckmann

Executive Digital Editor and Master Gardener

Catherine Boeckmann is the Executive Digital Editor of Almanac.com, the website companion of The Old Farmer's Almanac. She covers gardening, plants, pest control, soil composition, seasonal and moon c...
Read More from Catherine Boeckmann

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Comments

<span>Lillie</span> Fri, 07/08/2022 - 01:35
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.
<a title="View user profile." href="/author/editors">The Editors</a> Fri, 07/15/2022 - 15:15

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.

 <span>Cindy</span> Mon, 06/28/2021 - 15:37
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.
<span>Alicia Alicia Mccord</span> Mon, 05/31/2021 - 18:00
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.
<span>Heather Pens</span> Mon, 05/06/2024 - 17:44
My guess would be a fungus in the soil. I would guess the only thing to do would be to replace the soil and clean your tools. Ask someone that seems knowlegeable at a nursery about treating for fungus.
<span>Rox Shinobi</span> Tue, 12/01/2020 - 02:11
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.
<a title="View user profile." href="/author/editors">The Editors</a> Tue, 12/01/2020 - 15:10

Color changes in flowering plants is something of a mystery. It could be from limited chlorophyll or another component of photosynthesis. Some sources also suggest that temperature plays a role. 

If anyone has other explanations we'd love to hear them!

 <span>Terri</span> Fri, 11/20/2020 - 12:43
I've just moved from 6b planting zone to 9a. I've had 6 large planter pots across my back deck in full sun with petunias at both of my homes. In the 6b zone I would plant them from 4-6 inch pots or flats on June 15th (never before) after, hopefully, the last snow. They would bloom beautifully all summer long with minimal care needed; a little dead-heading, a couple miracle-grow shots. The pots would fill abundantly with lovely multi-colored flowers hanging all the way to the ground by mid July. Stunning! Bloom would usually be done by mid to end of September with the first cold bite. My new home this year in 9a. It's been a continual fight of aphids all summer long every 2-3 weeks with soapy water, store-bought remedies...I've tried everything. After each treatment, the plants lost their blooms and would look bare for a week or two, then abundant blooms would appear again (with aphids). It was cyclical. It's Nov 20th in 9a zone. We've had several frosts and the flowers and leaves still look good. I've read petunias may be perennial in this zone. We'll see. If they do, I may keep them, otherwise, any ideas on another full sun flower that doesn't have the pest problem?
<span>Shirley</span> Thu, 05/19/2022 - 16:26
I found Dr. Doom took care of the aphids. Works great on the ant problem as well. Hope this helps.
<a title="View user profile." href="/author/editors">The Editors</a> Tue, 11/24/2020 - 13:41

You should skip around this web site, Terri. Too many ideas to mention; here are a few:

•  https://www.almanac.com/best-flowers-window-boxes (it's containers by another name)

• https://www.almanac.com/content/container-gardening-flowers

• dated but timeless: https://www.almanac.com/march-jam-packed-new-plants-and-ideas

• https://www.almanac.com/seven-savvy-ways-get-most-out-container-gardens

• https://www.almanac.com/not-your-grandmas-coleus

We hope this helps!