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How Big Do Petunias Grow? (Plus Tips to Make Them Bigger)

How Big Do Petunias Grow? (Plus Tips to Make Them Bigger)

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One of the most prolific bloomers and most popular flowering plants, petunias represent a popular choice for outdoor landscapes and indoor gardens.

Petunias are found in every color except true blue, so you can find the perfect variety to fit your design and personal taste. They’re also easy to care for, so they suit novice gardeners.

But how big do petunias grow? And how tall do they get?

Can you encourage your plans to grow bigger or more flowers?

As someone who is fond of growing different petunia varieties, I’ll answer all your questions. So, let’s dive in.

How Big Do Petunias Grow?

Petunias can grow as annuals and perennials, depending on the climate. Most of the varieties you can find on the market are hybrids that come in various vibrant colors.

In optimal conditions, petunias can grow to be 24 inches tall and 36 inches wide, although some spread more than 48 inches wide. Yet, how big petunias will be depends on their type.


Grandiflora Petunias

Thanks to their big, not-to-be-missed blooms, these are the most popular petunia varieties.

The flowers have ruffled edges and can be four or even more inches across, and these varieties are available in single or double blooms. In some cases, the blooms can be more than five inches across.

These plants can be between 10 and 12 inches tall and sometimes reach a height of 15 inches. They’re popular as edging plants and can be used as a backdrop behind shorter plants.


Multiflora Petunias

Some popular varieties grow flowers as big as two inches across.

The Madness and Double Madness hybrids can have flowers that can be about three inches wide. These are popular hybrids of grandiflora and multiflora varieties.

Other varieties grow smaller blooms, but many flowers will be growing on the same plant.

Despite having smaller blooms, these plants are more tolerant of rain than grandiflora varieties. They can be grown as spreading plants or in containers, where they usually remain short.

Milliflora blooms are even smaller.


Spreading Petunias

Spreading petunias are commonly grown as a ground cover, where they spread to cover large areas in your lawn or backyard.

These varieties remain short, usually under the height of six inches and spreading for several feet.

How Tall Do Petunias Grow?

Petunias can grow in flower beds, baskets, and as cascading plants. The height of the plant depends on the growing conditions and the variety.

Some spreading petunias can be grown as a ground cover. They have a trailing habit, so they can grow from hanging baskets.

These varieties can grow to reach a maximum height of six inches. The Purple Wave variety grows large purple flowers, but it’s a spreading variety that can be under four inches tall.

Other varieties can grow as edging plants, which can be as tall as 15 inches. Most types reach a height of 18 inches in your garden, but some can reach a height of 24 inches with optimum care.

How Fast Do Petunias Grow?

You can plant petunias in the late winter for cool-season color or in the early spring for warm-season color, depending on their type.

Petunias are native to South America, so they achieve their best growth rate when the growing conditions in your garden or home mimic the conditions in their natural habitat.

Providing the plants with access to at least six hours of sunlight and protecting them from cold temperatures will encourage faster growth.

These beautiful plants are fast growers, typically reaching their full size in 10 to 12 weeks. So, if you plant them in winter, you can expect to see some beautiful colors in springtime.

However, the growth rate of your petunias depends on the method you choose to grow them.

Most homeowners grow petunias from young plants or transplants that they buy from nurseries. These plants will quickly grow and germinate when planted in a hanging basket or flower bed.

Within 12 weeks, you can expect to see the blooming flowers growing on your plant.

Growing petunias from seeds is more challenging and takes more time and effort. The seeds take about ten days to sprout, and the plants will grow within 12 weeks after being transplanted into the soil.

They should be transplanted to a pot or an outdoor garden flower bed when they have at least three true leaves. Otherwise, they won’t be able to survive.

Germination is also affected by the temperature.

When the temperature is between 75 and 85 degrees Fahrenheit, seeds can germinate within four days. In lower temperatures, germination can take up to 15 days.

How Long Does a Petunia Flower Last?

Petunias’ blooms appear in the spring after the last frost. They stay in bloom all summer and until the first frost in the fall, filling your garden with vibrant colors.

Maintaining warm temperatures keeps these flowers in bloom, and deadheading flowers will encourage more blooming.

Cutting off the spent flowers redirects the plant’s energy towards blooming instead of growing more foliage. However, some newer hybrids can continue blooming without deadheading.

These flowering plants can live in your garden or pots for up to three years with optimal care.

Why Are My Petunias Growing So Tall?

Tall plants or leggy petunias usually result from poor care and maintenance.

Lack of maintenance and pruning will direct the plant’s energy to grow taller stems, with only a few blooms appearing at their ends.

The sparse look means that you’ve neglected the plant for too long. Removing the spent flowers might save your petunia plant and encourage it to devote its energy to blooming.

Yet, in some cases, you’ll have to cut back the plant to half its current size. Although this procedure sounds drastic, it usually encourages your petunia plant to grow compactly.

Large petunia varieties are generally more prone to being leggy than the compact and smaller types. So, if you don’t want to prune your plant that often, you might have to choose a variety that grows smaller flowers.

How Can You Make Petunias Grow Bigger?

Pinching off a petunia plant will encourage it to grow bigger and fuller.

If you’re growing petunia from transplant, you should cut the top inch of the stems to encourage bigger growth. However, if you’re growing these plants from seeds, you should cut the top five to six inches of each stem.

Pruning and deadheading are also essential to encourage bigger flowers. You should get rid of all the dead blooms and wilting leaves to redirect the plant’s energy.

Finally, you can encourage bigger, healthier blooms by providing the plant with optimal care. This involves choosing fertile, well-draining soil, providing the plant with enough light, and watering it regularly.

Final Thoughts

Petunias are famous for their brightly colored flowers that can get as big as five inches across. However, some varieties grow smaller flowers.

The width and height of the plant depend on its variety, as spreading types can be too short. Yet, if you want to grow a bigger variety with larger blooms, you should pick a grandiflora petunia.

Petunias are fast growers, and you can expect to see their blooms 12 weeks after they’re transplanted. Luckily, these blooms can last all spring, summer, and even fall until the temperatures drop.

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