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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>Aslam Shaikh</span> Sun, 10/05/2014 - 09:18
Many thanks for your advise.Today I have officially planted the seeds in a plastic container, completely following your instructions,and have placed the container inside in a bright place after covering it with clear plastic. Now the question is how should I water it. A friend of mine told me to water it a little on every second day. Please advise before I mess it up. Thanks in advance.
<span>Bengy</span> Wed, 04/02/2014 - 13:06
I'm going to be re-planting the bed with new petunias, but wanted to check whether the dead-looking sticks (all that remains above ground from last summer), will come back to life and flower again this year... I know they are meant to be annuals so is this what they normally look like after their one season. Can I safely remove them and plant anew?
<a title="View user profile." href="/author/editors">The Editors</a> Wed, 04/02/2014 - 15:27

The petunias have died. Pull them out and prepare your beds. Amend the soil by digging in compost a 1- to 2-inch layer of compost. Plant them outdoors once the weather and soil have warmed up, about the time you plant impatiens or peppers.

 <span>Ms. Powers</span> Wed, 03/12/2014 - 16:08
I am teaching high school botany and for a class project, we are using varying environments to grow petunias to see the effect. In order to preserve the experiment, I need a controlled environment. I have everything the same, UV light, temperature, etc, but I cannot find an exact measurement for water. All the sites say to touch the soil to see if its dry. I need something a little more exact to preserve our controlled environment. Do you have a suggested amount or frequency we can use?
<span>Rajesh Khanna</span> Wed, 03/12/2014 - 22:22
one simple solution can be 1. weigh a few spoonfuls of the soil as it is, let it be w1 2. heat the soil, an oven can do the job, to lose the moisture. 3. weigh the soil again, let it be w2 difference in the two weights, w1-w2, will be the weight of water per w2 weight of soil, it is difficult to lose all the water from the soil and some may still remain attached to the soil even after lots of heating. But it is likely to be very little for most of the soils which are fit for cultivation and one can ignore that. one can go for very refined measurements also, with best regards Rajesh
<span>Helen Alen</span> Sat, 02/22/2014 - 01:53
I live in Southern Australia in a temperate climate. I planted petunia seedlings in late summer (that's mid February here). Do you think they will keep flowering into mid fall (April) when I want a nice display?
<span>Ritika</span> Wed, 02/19/2014 - 03:44
I have just bought new pink petunia with white lines on it, after few blooms the color of flowers have changed to purple and white. My purple petunia do not touch pink ones. I live in India, with max temp currently 27 C and min around 11 C
<span>Rajesh Khanna</span> Wed, 12/25/2013 - 03:24
Fresh leaves of some of my potted petunias are turning out to be yellowish and the plant does not grow after that. Even the flowers in these yellowish parts are very small and look sickly. The plant just stays the same, no growth, nothing, after this yellowness happens. The drainage is good, they get about 6-8 hours of sunlight, other nearby petunias, potted and cared for in the same way are doing well. Somebody has suggested putting some vinegar to make the soil acidic. Please help, I have noticed this problem in the last few years only in Delhi, India. Now i see the same in other people's petunias also.
<a title="View user profile." href="/author/editors">The Editors</a> Thu, 01/09/2014 - 11:58

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>Rajesh Khanna</span> Sat, 01/18/2014 - 00:04
thanks, will try rajesh