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Planting and Growing Petunias

Image Credit:
Pilat66/Getty Images
Botanical Name
Petunia spp.
Grown as
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

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 loves nature, stargazing, and gardening, so it’s not surprising that she and The Old Farmer’s Almanac found each other. She leads digital content for the Almanac website and is also a certified master gardener in the state of Indiana.

Read more from Catherine Boeckmann

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Comments

<span>Sheri H</span> Fri, 07/10/2015 - 14:19
My petunia flowers are getting smaller and the flower itself is curling backwards. How can I stop this?
<a title="View user profile." href="/author/editors">The Editors</a> Tue, 07/14/2015 - 08:57

If your petunia flowers are curling, it probably means a fungus is getting started. Water less, avoid overhead watering and water only at the soil level, increase air circulation, and spray with an all-purpose fungicide.

 <span>Helena Sawatzky</span> Wed, 06/17/2015 - 17:45
My petunias stay small and they look horrible they have good soil and I fertilize them and Water them and they just don't grow but they want to bloom and I do cut the stems off
<a title="View user profile." href="/author/editors">The Editors</a> Tue, 06/23/2015 - 10:22

It sounds like you are on top of the watering situation. Hopefully, they are getting enough sun. Try cutting them back, which will encourage bushier growth. Petunias are heavy feeders and grow best with a soil pH between 5.5 and 5.8. With a higher soil pH, petunias begin to suffer from iron deficiency. Try fertilizing with a fertilizer rich in iron.

 <span>Beginner</span> Mon, 06/15/2015 - 22:03
Hi all petunia lovers, I planed my wave petunia (which said it can spead out 3-4 feet) for 2 months and can't wait to see it spill down from my deck but it has not. When I first grow i headdead them and they bloom like crazy but they don't spill down. My husband said since I headdead them the plants focus on producing more flower and won't grow long, is it true? Thanks!
<span>Karen Holroyd</span> Sun, 06/14/2015 - 10:49
My petunias are in a hanging basket and are in full bloom. The flowers are fine but I've noticed lately the leaves are turning yellow, especially at the base of the container. They weren't doing this for the first month or so, but it seems to be getting worse now that the weather is warmer. Any suggestions? Thanks.
<a title="View user profile." href="/author/editors">The Editors</a> Tue, 06/23/2015 - 10:24

Have you given your plants any fertilizer? Petunias are heavy feeders and grow best with a soil pH between 5.5 and 5.8. With a higher soil pH, petunias begin to suffer from iron deficiency. Try fertilizing with a fertilizer rich in iron.

 <span>Debbie Mcgee</span> Thu, 06/11/2015 - 13:09
I have multiple colors and types of petunias in about 15 pots/window boxes that I purchased from a hardware store. Once I got them home, I quickly saw that the flowers were being eaten by something. I do not find any evidence of bugs or caterpillars, but have been spraying the plants daily with Safer caterpillar killer. I also deadhead the flowers that are affected, but I am not seeing an improvement. What is going on with my plants and how can I treat it?
<a title="View user profile." href="/author/editors">The Editors</a> Fri, 06/12/2015 - 14:18
Hi Debbie, You probably have some night visitors. Go out after dark and check for earwigs or slugs. They usually hide during the daytime and come out when it's dark.
<span>Sara Carnes</span> Sun, 05/31/2015 - 20:15
Some of the branches in my Purple Wave petunia are sprouting blooms that are a mottled green and purple, almost tie-dyed looking. Is that normal, or a sign of a mutation? Or maybe even a deficiency?