How to Care for Petunias

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It isn’t surprising that petunias have been a garden favorite for generations. Their wide range of colors, their willingness to bloom all summer with non-stop flowers, and their simple needs make these annuals a popular choice for seasoned and novice gardeners alike.

Planting petunias is easy, and if you make sure to give them the proper care, you will find that anyone can grow petunias! No green thumb required.

Petunias can be planted in beds and borders, containers, and hanging baskets.  Let’s look at some of the different petunia varieties to see how they can best perform in your garden.

Choosing A Petunia Variety

A petunia is not just a petunia.  When growing petunias, some varieties are better in pots and containers, while others are better for flower beds. 

Consider the following varieties:

  • Multiflora petunias are big bloomers with 2-inch flowers.  They are compact and need minimal pinching.
  • Grandifloras have very showy 5-inch blooms, but they have fewer flowers than Multifloras. Most are 12-15 inches tall and some have a trailing habit, like cascading petunias.
  • Floribundas are a cross between Multiflora and Grandiflora with big flowers and the ease of care like Multifloras.
  • Millifloras have small 1-inch flowers and are suitable for containers as they only get 8 inches tall.
  • Waves are spreading petunias that make a beautiful annual ground cover that needs very little care. They grow only 6 inches tall, but can spread to 4 feet!  Purple Wave was the first of this variety, but now there are many flower colors to choose from today.
10 pinkish-purple petunias are in bloom

And then there are petunia’s cousins:

  • Calibrachoas are closely related to petunias, but they are not little petunias.  Often sold as Million Bells, calibrachoas have different moisture and fertilizer requirements than petunias, requiring more frequent waterings and a light application of fertilizer each time. They are also more tolerant of frost than petunias. 
  • Patchoas are a cross between calibrachoas and petunias. They have a semi-trailing habit and are good for hanging baskets and containers. A patchoa also has better heat tolerance than a petunia or calibrachoa.  They produce flowers all summer long and need very little pruning or grooming. Their water requirements are the same as petunias.
  • Ruellia humilis is a wild petunia that is perennial and hardy in zones 4 to 8. While not as showy as hybrid petunias, this plant can be a fun addition to your garden. It has purple flowers and grows between 1 and 2 feet high and wide.
The picture is full of dark purple petunias in a garden

Growing Petunias from Seed

You can grow petunias from seed, but it’s not an easy project. The seeds are tiny and difficult to handle. They take a while to germinate and are picky about light, temperature, and water requirements. The growing trays, starter soil mix, and grow lights cost much more than a cell pack of pretty plants ready to get growing in your garden right away.

But, if you want to try anyways…

  1. Start petunia seeds indoors 6 to 10 weeks before the last frost date for your area.
  2. Fill your planting tray with seed starting mix or a light, soilless mix.  Moisten the soil.
  3. Because petunia seeds are so small, mixing them with a little sand will make it easier to work with them.
  4. Spread the seeds out on top of the soil and use a spray bottle to mist the seeds lightly.  Petunia seeds need light to germinate, so don’t bury them in the soil.
  5. Cover the seed tray with a clear plastic dome or a piece of plastic wrap.  You want to keep the seed bed constantly moist until the seedlings emerge, so keeping misting them with your spray bottle if they start to dry.
  6. Place the seedling tray in a warm, bright area.  If you are using grow lights, they should be kept 4 inches above the petunias as they mature.
  7. In 7 to 10 days, your baby plants should sprout. Remove the cover but continue to keep them moist.
  8. When the seedlings have three true leaves, you can step them up into little pots.
  9. Let them grow on until you are ready to plant outdoors when frost is no longer predicted.

Planting the seeds directly in your garden is not recommended.  If you try this, your petunias will take a very long time to grow. Several weeks of summer could pass before you start to see blooms on your plants!

Three petunias seedlings are in plastic containers ready to be planted

Buying Petunia Plants

Most of the time, it’s easier to just buy petunias plants to plant into your garden

At the garden center, look for petunia plants with only a few, if any, open flowers, and only a few buds.  Buy these plants when they are still green. The smaller the petunia plant is when you bring it home, the better it will take off. 

Don’t buy a petunia that has stringy foliage going over the edges of the pot, and avoid a plant with a floppy “neck.”  Look for a petunia plant that is strong and sturdy, tight, and compact.

Store-bought dark pink petunias each that is very healthy-looking and young.

Planting Petunias

Planting Petunias in the Ground

Plant in full sun after the danger of frost has passed.  They will be happier in warmer, drier soil, so wait to plant if the weather has been wet and chilly.  Most varieties should be planted about 10 inches apart in a garden bed for a beautiful lush display. Spreading petunias (like wave petunias) can be planted further apart – 1-½ or 2 feet – depending on how quickly you want them to fill in.

Planting Petunias In Containers And Hanging Baskets

Plants can be spaced closer together to give an instant show.  In a 12-inch hanging basket, 3 to 5 petunia plants will produce a beautifully abundant display. Make sure to use a high-quality potting soil in your containers and baskets.

Pink and purple petunias that are in a small container

Growing Petunias

While it’s easy to grow petunias, they do have some requirements.  Luckily, meeting these requirements is not hard. Give your petunias all that they need, and they will keep the flowers coming.

Plant in Well-Drained Soil

Petunias like well-drained soil.  Sandy or clay, acidic or alkaline doesn’t matter much to them, but well-drained soil is a must! Petunias do not like “wet feet.” 

In a flower bed or border, petunias will do just fine in average garden soil.  In containers and hanging baskets, they are happy in a soilless mix.

Petunias Should Be Planted in Full Sun

Petunias love full sun.  That’s at least six hours of sunlight a day.  In very hot climates, petunias may need a little shade in the late afternoon to keep producing flowers.

Let Your Petunia Dry Between Waterings

A bunch of pink-purple petunia flowers fill the image

Your watering habits are the most critical element to the success of your petunias.  The best way to water petunias is to water them deeply and then leave them alone until the top inch of soil is dry.  They like it dry and should be ignored until that top inch is dry.

Check your plants daily if they are in containers or twice a week if they are in a garden bed by simply sticking your finger in the soil. 

If you underestimate and the petunias wilt, don’t worry – give them a drink and they’ll bounce back quickly. When you water, try to water just the soil, not the petunia foliage or the petunia flowers.

Frequent Fertilization

Petunias are heavy feeders and need regular applications of a balanced liquid fertilizer (for example 10-10-10). You can check out our top recommendations for petunia fertilizers.

Petunias in containers and hanging baskets need feeding weekly; in garden beds, feed every other week.  Give your petunias two to three weeks to get settled in your garden before you start a liquid fertilizer regimen.

Prune Your Petunias

To keep your petunias looking good, take some time to groom them. 

As the summer progresses, petunias can get tired and leggy. Petunias bloom their best when they receive 10-12 hours of daylight.  As the summer light starts to grow shorter, this sends a signal to petunias to stop blooming and set seed.  We can “trick” petunias into a new flush of growth (and more flowers!) by shearing them back. Cut off all the stringy, trailing stems that have only a flower or two. 

So, don’t be afraid to give them a good haircut in mid-August.  With an application of liquid fertilizer and a thorough watering, they’ll be flushing out like it’s springtime again to give a repeat performance in a week or two.

White petunias planted in a white glass pot

Petunia FAQ

How do you take care of potted petunias?

Growing petunias in pots require a slightly different approach than growing these plants in the ground.  First, use good potting soil. Your plants will need more frequent waterings and fertilizer applications.

Do petunias need deadheading?  

Yes! Deadheading petunias keeps them tidy and encourages them to keep blooming. The job of any plant is to reproduce – to set seed to make next year’s plants and petunias are no exception.  Removing dead flowers from the plant keeps it from setting seed.

Red and pink petunias in a brown container

How do you keep petunias blooming?

Deadheading and cutting away unproductive stems will encourage petunias to keep producing flowers.  Regular fertilizer applications help, too. When your plants start to look stringy and leggy and have very few flowers, trim them back.

Can you overwater petunias?

Yes, it’s very easy to overwater petunias. There are so many annuals in our summer garden that need an abundance of water that sometimes we think petunias need a lot of water, too. But they like to dry out between waterings.

How long do petunias bloom? 

Petunias can bloom from the last frost in spring to the first frost in autumn with the proper care.

How long do petunias live?

Petunias are perennial in USDA zones 10 and 11.  For the rest of the U.S., petunias are an annual and will live from the last frost to the first frost, or perhaps a little longer.  Once petunias are hit with frost, they won’t make any more flowers.

How do I protect petunias from frost? 

Some petunia varieties can handle a light frost or two without any protection. If frost is predicted in your area, you can cover your plants with an old bed sheet or something similar the evening before.  Once the sun is up and the frost lifts, you can remove the covering. 

Dark purple and white petunias in a hanging pot.

How do I propagate petunias? 

Petunias can be propagated from vegetative cuttings and from seed.  Some varieties are trademarked and propagation is prohibited.

Do Petunia have insect or disease problems?

Petunias are sometimes troubled by insects, mainly budworms, aphids, and slugs. Diseases are mostly cultural problems – mildews and rots – that can be managed with proper cultural practices.

Happy Planting!

About the author: Carley Miller is a horticultural expert at TheGreenPinky. She previously owned a landscaping business for 25 years and worked at a local garden center for 10 years. Read More

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