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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

<a title="View user profile." href="/author/editors">The Editors</a> Mon, 06/10/2019 - 16:37

Insecticidal soap, neem oil, or horticultural oils will rid the petunias of many insect pests. You can make your own insecticidal soap or buy it at a garden center. Neem and other oils can be found at garden centers.

 <span>Edith Smith</span> Tue, 05/07/2019 - 10:00
Its a question . can I spray guard tech seven on my seeding petunias
<span>Judy Reavis</span> Sun, 06/09/2019 - 14:04
MY GERBER DAISIES HAVE HOLES IN THERE LEAVES FROM AN INSECT OF SOME KIND. I HAVE "INSPECTED" THEM AND CAN,T FIND ANY EVIDENCE OF A CRITTER. I HAVE SPRAYED SEVEN AND USED SNAIL BAIT. ANY SUGGESTIONS?
<span>Cindy Smith</span> Thu, 07/11/2019 - 08:08
I put sand around any plants affected by slugs.
<span>Cynthia Kukler Smith</span> Thu, 07/11/2019 - 08:05
I put sand on top of my soil for daisy and hosta, if its snails, you can also put a small container out close to plant and fill half full with beer ,lol it works but try sand first .
<span>Karen Irwin</span> Sun, 06/23/2019 - 10:05
Not sure what zone you are in, but in zone 4 there has been massive amounts of rain, also flooding in some areas. The water table underground has raised up and is pushing the ant population upwards to the surface. We are over run with ant hills all over the place. They eat the leaves of plants and trees leaving holes throughout the tender leaves. It is a huge problem this year. This could be your mysterious insect culprit. Check around for evidence of ants and treat accordingly. The best deterrent by far is peppermint. I use the oil drops on my window and door sills, fresh/dried leaves sprinkled around my house, plants in the garden. Good luck, happy gardening!
<span>Tatyana</span> Wed, 07/03/2019 - 12:05
Do regular fresh mint leaves work as well?
<span>Priscilla</span> Sun, 05/19/2019 - 19:18
Check our 12 uses of vinigar. Most enlightening. Animals don't like the smell. Solutions for a variety of insects even fruit flies. Try looking up the uses for Baking Soda from sprays to fertilizing plants. These are similar tol organic methods
<span>Kathy</span> Wed, 01/09/2019 - 13:21
We want to use planter boxes of petunias at my son's wedding in May. When should I start the seeds "inside" to insure we have full flowered beautiful boxes of petunias?
<a title="View user profile." href="/author/editors">The Editors</a> Fri, 01/11/2019 - 09:38

Now. And keep you fingers crossed. Petunias are extremely slow to germinate, some 5 to 15 days at normal temps in the house. To hasten things, put the sprouts under a fluorescent light for 12 hours per day to mimic spring conditions. Many sources advise starting seeds 6 to 10 weeks before the last frost and then transplanting to let them mature. But you probably want mature plants in bloom for this event, not seedlings. If we may make a suggestion: Start your seeds and see how it goes (pls let us know!) but be ready to buy plants for the windowboxes—and give the individually potted/ready-to-plant seedlings to guests as a remembrance. Best wishes!