How to Care for Petunias

Raising beautiful petunia flowers is not difficult. Use our practical tips on the Green Pinky to help you develop beautiful blooms.

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

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

Choosing A Variety

When growing petunias, some varieties are better in pots and containers, while others are better for flower beds. 

Consider the following varieties:

  • Multiflora varieties 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.
  • 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.

And then there are some closely related flowers:

  • Calibrachoas are closely related, but they are not little petunias.  Often sold as Million Bells, calibrachoas have different moisture and fertilizer requirements, requiring more frequent waterings and a light application of fertilizer each time. They are also more tolerant of frost. 
  • 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 them.  They produce flowers all summer long and need very little pruning or grooming. Their water requirements are very similar.
  • 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.

Growing 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 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 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.  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 your seedlings 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 your flowers will take a very long time to grow. Several weeks of summer could pass before you start to see blooms on your plants!

Buying Petunia Plants

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

At the garden center, look for 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 plant is when you bring it home, the better it will take off. 

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

Planting Petunias

Planting 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 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 plants will produce a beautifully abundant display. Make sure to use a high-quality potting soil in your containers and baskets.

Ongoing Care

While it’s easy to grow petunias, they do have some requirements.  Luckily, meeting these requirements is not hard. Give them 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! They do not like “wet feet.” 

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

Plant in Full Sun

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

Dry Between Waterings

Your watering habits are the most critical element to your success.  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 your plants 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 foliage or the flowers.

Fertilization

They 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 plants two to three weeks to get settled in your garden before you start a liquid fertilizer regimen.

Pruning

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

As the summer progresses, petunias can get tired and leggy. They bloom best when they receive 10-12 hours of daylight.  As the summer light starts to grow shorter, this sends a signal to stop blooming and set seed.  You can “trick” them 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.

FAQ

How do you take care of potted petunias?

Growing 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 you need to deadhead them?  

Yes! Deadheading 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.

How do you keep them blooming?

Deadheading and cutting away unproductive stems will encourage them 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 them?

Yes, it’s very easy to overwater. 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 they bloom? 

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

How long do they live?

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

How do I protect them from frost? 

Some 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. 

How do I propagate them? 

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

Do they 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.

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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.

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