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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>John Dumancic</span> Tue, 05/17/2016 - 09:49
Yesterday, I bought a small spreading Petunia plant in a 4 inch by 4 inch pot. How should I transplant it into the ground? Also, overnight, some blossoms closed up. Should I deadhead these?
<a title="View user profile." href="/author/editors">The Editors</a> Tue, 05/17/2016 - 15:47

In general, you can plant spreading petunias about a foot or so apart, unless you are transplanting into a container, in which case you can crowd them a little more. Full sun and moist, but not waterlogged, soil is ideal. Some spreading types can cover an area 3 to 4 feet at maturity. See above article for general care. In general, deadhead any flowers that are withered and browning, to encourage blooming. Some spreading types, however, such as the Wave series, do not require deadheading for vigorous bloom.

 <span>R K Traut</span> Wed, 04/13/2016 - 17:26
Will cuttings from petunias root ?
<span>Chrissy Whalen</span> Tue, 05/31/2016 - 10:36
We bought 8 petunia plants this April and cut the larger shoots off. Planted in soil with rooting powder and kept well lit and watered. More than half took and saved us the expense of having to purchase more. Also, when planting if a stem breaks off just stick in the soil it will root.
<a title="View user profile." href="/author/editors">The Editors</a> Thu, 04/14/2016 - 14:49

We have never done it, RK, but we are told that you can root petunias in water or in soil; if using soil, rooting powder is recommended. Here's more specific information: http://4h.wsu.edu/em2778cd/pdf/pnw0151.pdf

 <span>Tanya Alexander</span> Wed, 04/06/2016 - 15:49
Hello! I have purchased 1 each of Crazytunia Kermit Purple Petunia, Cascadias Indian Summer Petunia, Cascadias Bicolor Rim Violet Petunia, and Crazytunia Star Jubilee Petunia, from GardenHarvestSupply. As they all have contrasting colours, I was hoping to plant them in flower box. Would that be advisable? I haven't received the plants yet, so I'm hoping to purchase the necessary container(s) based on your advise! The plants should be arriving in about a week, so please let me know at your earliest convenience! Thank you so much!! Here are some details: 1) Crazytunia Kermit Purple Petunia Plant Care and Growing Information Mature Height: 20-40 inches Mature Spread: 15-20 inches Exposure: Full Sun Bloom Time: Early Spring - Fall Soil Moisture: Moist Soil Type: Widely Adaptable 2) Cascadias Indian Summer Petunia Plant Care and Growing Information Mature Height: 8-20 inches Mature Spread: 36-48 inches Exposure: Full Sun - Partial Shade Bloom Time: Early Spring - Early Fall Soil Moisture: Moist Soil Type: Widely Adaptable 3)Cascadias Bicolor Rim Violet Petunia Plant Care and Growing Information Mature Height: 8 - 30 inches Mature Spread: 4 - 6 feet Exposure: Partial Shade - Full Sun Soil Moisture: Moist Soil Type: Widely Adaptable 4)Crazytunia Star Jubilee Petunia Plant Care and Growing Information Mature Height: 10-15 inches Mature Spread: 10-12 inches Exposure: Full Sun - Partial Sun Bloom Time: Late Spring - Late Fall Soil Moisture: Moist Soil Type: Widely Adaptable
<a title="View user profile." href="/author/editors">The Editors</a> Fri, 04/08/2016 - 16:36

What a nice idea to plant these beautiful petunias together in a flower box. Pay attention to height and spread for each variety. Plant the taller varieties in the back and the ones that spread or cascade on the outsides of the flower box. Good luck!

 <span>Roozbehahmadi</span> Tue, 03/22/2016 - 00:45
Hello I am from Iran. I want a collection of plants and flowers photo with environmental needs. Can you submit them to this above email. Thanks you.
<span>Jackyager</span> Fri, 03/11/2016 - 10:00
I start my petunias from seed and after they get leaves the stem seems to be off the roots ive used different kinds of starting soil but all the same what am I doing wrong.Thank You Jack Yager
<a title="View user profile." href="/author/editors">The Editors</a> Mon, 03/14/2016 - 15:03

Jack, this is called damping off, and it can be caused by several things, often poor soil/growing matter, too much moisture, too cold soil, compacted soil/medium, lack of air circ (see moisture), even diseased containers. We recommend that you start again; it's still early in season!