Are Petunias Considered Annual, Biennial, or Perennial Flowers?
Thinking of planting some petunias this season but aren't sure if they'll come back each season, or you'll need to replant them year after year? Petunias are a garden favorite, and their low-maintenance blooms are always a welcome addition to any flower garden. In this article, we define the petunia based on your growing location, and if they are considered annual, biennial, or perennial plants!
It’s easy to fall in love with petunias. These pretty add color to borders and garden beds. They are also easy to grow as long as they have plenty of sunshine and enough water. But, are petunias annuals or perennials?
Petunias can come back each year in some climates, but in other regions, gardeners need to sow seeds in the early spring. The plants are temperature-sensitive, forcing most growers to treat petunias as annual plants.
Whether you plant petunias as annuals or perennials, we’ll cover everything you need to know about growing these popular garden plants. Let’s dig into the details about these popular flowers and their life cycle!
The Short Answer
Petunias are grown as both annuals and perennials, depending on the hardiness zone they are grown in. They are technically classified as tender perennials but grow as annuals in colder climates as they cannot tolerate frost. US hardiness zones 9-11 are best for growing petunias as perennial flowers. These zones do not get cold enough to frost over.
The Long Answer
Even though the bushy plants are often grown as flowering annuals, petunias can be tender perennials that grow from new plants and cuttings. This is the most common way to grow them.
In warmer climates, petunias are year-round plants that add garden color from spring through winter. But even in warmer climates, they are treated as annuals despite their tolerance for drought. Most varieties can handle temperatures down to 40°F without too much damage, but some species are harder. For example, Wave petunias can withstand temperatures dropping down to around 35°F.
Petunias are a garden favorite and are considered annuals in many hardiness zones. Most varieties cannot survive temperatures below sub-freezing, around 40°F.
These plants are tropical natives and do not have a dormancy stage. In ideal locations, petunias will bloom continuously for up to 12 to 18 months. Once all of the blooms are spent, the plant dies and does not return.
Petunias in tropical regions can be treated as short-lived perennials, and it’s the reason most gardeners treat them as annuals, who expect to replace the plants every spring. Petunias can also self-seed in the ground, but the returning plants are often scarce.
Petunias are tropical plants and tender perennials in hardiness zones ten, eleven, and above. These warmer climates are found in the deep south and along the southern United States coast. Everywhere else, petunias are annuals.
In zones ten and eleven, growers can often enjoy a year of blooms or longer. Petunia seeds need a steady temperature of 70°F to 80°F for successful germination. It’s one of the reasons why warmer climate gardens see up to 18 months of petunia flowers.
Petunias also grow in cooler climates, but only as annuals. Nighttime temperatures cannot fall below 55°F. Daytime temperatures also have to remain at or above 65°F for petunias to thrive in the garden.
The flowering plant’s life cycle is influenced by sunlight and temperature. Warmer temperatures help extend the flowering cycle and the life of the plant. It’s reverse in cooler regions, where petunias only live for one season.
Dormancy and Overwintering
Petunias do not enter a true dormancy period – their life cycles are too short as annuals. It also applies when you are trying to grow petunias as perennials.
A plant’s dormancy period typically occurs in the winter. The plant goes to sleep for a few months. Your plant uses the time to build up the nutrients necessary for regrowth.
A sign of dormancy includes the plant’s foliage dropping off. Some plants also die back to the ground, leaving only the roots intact in the soil.
Since petunias are inexpensive garden plants, and widely available, most growers treat them as annuals. They expect to replace their petunias every spring, but some cultivars are slightly pricey for a small garden plant.
Growers with one of the more expensive petunia varieties may want to overwinter the plant. Its tropical nature and relatively shallow root system mean you can’t use protective measures in the garden. Even a thick layer of mulch doesn’t provide enough insulation against freezing temperatures. The roots grow too close to the soil surface.
Growers that want to keep their petunias alive through the winter can bring them indoors. There are a few downsides to overwintering petunias, such as not being able to overwinter petunias planted on the ground. The shock the plant gets when it’s removed from the soil, and placed in an indoor pot, is usually too much for petunias.
Some growers plant petunias that they want to overwinter in pots. This way, when cooler temperatures hit, they can easily move the potted plant inside where they can survive.
It is best to cut the petunia back before bringing it indoors. Trimming it back to around two inches above the soil helps ensure healthy growth in the spring.
Water the pot before placing it in a cool and dark location. Wherever you overwinter your petunia, make sure the temperature stays above sub-freezing.
It’s also a good idea to moisten the first layer of soil every three or four weeks. You only want to give the plant enough water to keep it alive but prevent it from starting to grow. In a way, you are forcing the petunia into an unnatural dormancy period.
Depending on your available storage space, it might be easier to overwinter petunias as cuttings. Petunia cuttings root easily, but you want to get them before the first light freeze. Even a dusting of frost can kill tender petunias. Here’s a quick overview on how to take petunia cuttings:
Steps For Taking Cuttings
- Look for stems around three inches and make a clean cut.
- You can root the stems in water or soil.
- It’s a little easier in soil, but you can see the roots developing in water.
- If you are using water, only place one stem per glass.
- The roots can grow together, and they are hard to untangle.
- Remove the bottom leaves before placing the stems in the soil.
- It typically takes around three weeks for roots to develop.
- Once the stems are developing roots, move seedlings to a sunny window.
As soon as all danger of frost has passed, you will want to follow a process called “hardening off.” This gives your petunias some outdoor exposure prior to planting them directly in your garden beds.
Growing as Perennials
Perennial gardens have certain advantages that include the same plants growing back each year. You know what to expect, and perennial plants are often easier on your wallet – you aren’t buying new plants each spring. Petunias can grow as perennials in certain climates.
Petunias are picky about the temperature. They thrive in regions with warm winters and summers that stay below 90°F. High heat will burn the plant, causing it to wilt. The foliage often turns brown before falling off.
The best time to plant perennial petunias is in the fall. The bushy plants will continue producing flowers until summer temperatures get too high. If your summers are relatively cool, petunias will keep blooming.
The plants thrive in full sun. Petunias have a habit of becoming leggy when sunlight is missing. A lack of adequate sunlight can also inhibit blooming. Flowers are often smaller and not as profuse. The blooming period is often shorter for these petunias.
Some growers start their petunias from seed, and it’s not easy. The minuscule seeds are easy to lose. The seeds also need specific temperatures for germination, and Mother Nature doesn’t always cooperate.
It’s easier to start the seeds indoors, about two months before the last frost. Give the soil an additional two weeks to warm up before planting the seedlings in the ground.
Growing as Annuals
There’s a single reason why petunias are commonly grown as annuals – their temperature sensitivity. As tropical plants, petunias do not like cold or hot weather, which limits where they can grow as perennials. It’s also a bit of a pain to overwinter the inexpensive garden plants.
How to grow petunias as annuals depends on your climate. In cooler zones, it’s best to plant petunias in the spring. Make sure you wait until all danger of frost has passed. The annuals will typically bloom from late spring into the fall, as long as summer temperatures stay below 90°F.
In warmer climates, petunia growers usually put the plants on the ground in the fall. Instead of waiting for frost danger to pass, these growers are looking for signs of falling temperatures. The plants will bloom in warmer climates through the fall, winter, and spring and dies out when high summer heat returns.
The growing conditions are the same for annual petunias as perennials. The plants need at least six hours of full sun for optimal growth. Sunlight is also a requirement for plants to bloom. When annual petunias are planted in the shade, you may not see any blooms.
Pinching dead flowers from the plants can extend the blooming period. It also helps the plants keep their attractive, bushy shape.
Petunias are popular garden plants commonly grown as annuals due to their sensitive nature. They do not like hot or cold temperatures, which is why the tender perennial is treated as an annual.
Gardeners in hardiness zones outside ten or eleven may want to look at the cultivars. Many hybrids are specifically bred to withstand some extreme temperatures. It’s also where you find the double-bloom petunias and other specialty varieties.