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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>By Anonymous</span> Mon, 05/27/2013 - 11:40
When the flower has bloomed, do you pull the flower off or do you cut the flower and stem off at the base of the main stem?
<a title="View user profile." href="/author/editors">The Editors</a> Fri, 05/31/2013 - 16:53
Prune petunias back severely—so, yes, at the stem—for new shoots and flowers to develop. However, do not prune trailing petunias (the type that drape).
<span>Vincent Athens</span> Thu, 05/23/2013 - 12:45
As being a Dutch guy (you love flowers because you were born in the worlds flower capital) living now in Athens Greece I have to say I love Petunias. I use to buy them already full grown with flowers but I noticed that about 1/3 of them died. OK you have to understand that I live on the top floor where they have the whole day sun light plus a lot of wind (300 meters away from the sea) and temperatures from end April around 30c with max temperatures till 45c in July and August. This spring I seeded for the first time my own Petunias and I was concerned about the microscopic little seeds. I believe we must had added at least 20 seeds together in a seeding tray. When they grew up I took some out, put them in water to loosen up there roots and separated them. I tell you only one survived this way while the others (with app. 20 seeds)are doing very well and have lots of flowers. So my advice use lots of seeds together and you will get a very nice mix of colors. I have them growing in pots and they are connected to an automatic watering system. Now in May with temperatures between 27c and 32c they get water every 12 hours (they receive at least 10 hours of direct sun light per day) for 3 min. From end June they will be watered every 6 hours for 3 min (believe me they need that with this kind of heath that we have in Athens). Also I have a special device to add liquid fertilizer into the automatic watering system (about every 10 days) which works very well. For my balcony Petunias are super plants but at the same time I would love to have some advice on other flowers/plants that would do fine in the above described climate conditions. One more important advice: check each day for (almost) dead flowers and pull them gently out. Don't use force, if you can't get them out in an easy way then you will leave them and pull them out 1 or 2 days later.
<span>Anonymous</span> Fri, 05/17/2013 - 19:19
How can I save seed from my petunias? I have never seen any but can purchase seed every spring. I save my seed from all my plants wherever possible
<a title="View user profile." href="/author/editors">The Editors</a> Tue, 05/21/2013 - 17:13
You can save petunia seeds, however, over 99% of these flowers are hybrids so do not expect to get the same plant type or color combination. It will be an experiment! It's easy to save the seeds. After the plant dries up, snap off the dried flowers and the seeds will pour out. Petunias often reseed themselves, too.
<span>Anonymous</span> Thu, 05/09/2013 - 18:06
Do lady bugs kill the flowers??
<span>Anonymous</span> Tue, 05/14/2013 - 11:24
No! Lady bugs are actually GOOD for flowers. Some green houses even sell lady bugs for flower beds!
<span>Anonymous</span> Fri, 03/15/2013 - 07:55
These flowers grow beautifully and very easily in Pakistan. The weather is just perfect. The only thing is that you will need to water them 2-3 times a week.Pakistan is one of the very few countries that grows mangrove trees abunduntly and easily so the soil is perfect.