How Fast Do Petunias Grow? (Getting to Know About Petunias)

Petunias are one of the most planted flowers thanks to their beauty. You could hold a contest asking people to choose a flower, and petunias would come out tops. It’s bright, lively, and provides a lovely fragrance and a magnificent bloom.

Although initially of South American origin, no one would blame you for using it. Today, petunias are the most favored flower in North America. 

So, in case you’re looking towards planting petunias. And you’re wondering how fast they grow, or how long it will take. Don’t worry. We got you covered. 

In this post, we’ll tell you all there’s to know about how fast petunias grow. Let’s go!

Getting to Know About Petunias

It’s only fair that you know more about what you’re trying to plant. So, what are petunias?

Like you know, they are flowers, beautiful flowers. There are also a variety of petunias, over a hundred. And this means that you can enjoy various options when thinking about beautifying your garden. 

However, this flower that’s a member of the family – Solanaceae – comes in four categories. They are

  • Grandiflora 
  • Multiflora
  • Miliflora
  • Spreading or groundcover 

How Quickly Do Petunias Grow?

If you’re looking to understand the rate at which petunias grow, you’ll need to assess how you grow them. This is because the growth speed depends on how you grow petunias.

Generally, there are two ways to grow petunias. And this can either through transplants or from seeds directly. You should know that seeds take more time compared to transplants.

Growing from Seeds

If you pick this method, you can expect your seeds to take between 7 and 10 days to germinate and sprout. Also, it takes between 10 and 12 weeks from when you plant the seeds to when flowers begin to grow.

You’ll generally need to account for as much as 12 weeks before your actual outdoor planting. 

Growing from Transplants

If you pick this method, you’re reducing the effort and time you need. In such cases, you don’t need to start the whole germination process. All you need to do is purchase an already germinated petunia. And then you can easily just transplant it to your garden bed, pot, or hanging basket.

This method allows you to save as much as 12 weeks in growing time.

How Long Do Petunias Take to Grow?

Generally, the germination of petunias takes between 5 and 15 days. And this is where the room temperature is average. That is, between 68 and 72 Fahrenheit. 

In cases where the temperature is warmer, and between 75 and 85 Fahrenheit you can achieve germination in four days. 

How Big Do Petunias Grow?

Like we stated earlier, petunias come in four categories. And these categories are what determine how big petunias grow. So, if you’re looking for a particular size, you’ll need to ensure you pick the right type.

So, you know what you’re doing, here are the four categories and how big they grow. 


This category turns out as the biggest. Usually, they are between 3 and 5 inches in width. They are then generally between 10 and 12 inches tall, sometimes 15 inches. So, if you’re looking for a tall and big petunias, this might be the best bet.


This category isn’t as broad as the Grandiflora category. However, they are usually abundant. They can generally grow between 1 and 2 inches width-wise and as much as 8 inches in height.


This category also produces small flowers like the multiflora category, although smaller. Regardless, it compensates for this with its generous quantity. It’s usually about 1.5 inches in diameter.

They are usually best utilized as edging flowers or plants. You can also mix them with other flowers – annuals – in a container.

Spreading Petunias 

In case others refer to this category as groundcover petunias, they are also right. This category is usually around six inches in height. And it naturally spread, covering a large area within a growing season.

In most cases, it spreads so widely that you might be unable to identify the foliage. 

How Long Before Petunias Bloom?

Usually, petunia seeds need quite an amount of light before it can germinate. So, if you’re looking for bloom, you’ll need to give them light.

After this, it will take between 6 and 8 weeks for your plant to bloom. So, start the planting process indoors. And ensure it’s in a fertilized and moist soil.

You can transfer the plant outside after between 10 and 12 weeks have elapsed. It would be best if you wait to have at least three leaves on the plants before transplanting them. 

Does Temperature Affect the Growth Rate of Petunias?

Yes, the temperature of the area affects the growth rate of petunias. Usually, when temperature increases, petunias grow faster. Precisely, petunias need heat for optimal growth.

In case you’re looking to get the best result, use warm areas. That is, between 65- and 75-degrees Fahrenheit. It would be best to expose your plant to sunlight for as much as 16 hours.

Also, in cases where there’s a cool temperature, below 65 degrees Fahrenheit, as long as the day is long, it would still grow fine.

Also, where the day is short, as long as the temperature reaches 75 degrees Fahrenheit, and there’s 8 hours sunlight, it’s all good. 

How Long Do Petunias Last?

As an answer to your question, petunias can last between 2 and 3 years in warmer climates. However, the fact is that in the real sense, petunias are annuals in cold climates. As such, they might be unable to survive the cold temperature that comes with winter. 

So, if you intend to give your petunias a two to three-year lifespan, you’ll need to ensure they are away from the cold. The best way to get this done is to keep them indoors.

To do this, all you need to do is a plan. This will require you to plant the petunias in a small container. 

In case you already have them on the ground, you need to transfer them to a container. So, dig your petunias up, carefully, then repot your petunias. 

Also, ensure you do this before winter arrives. So, it would be best to do this during Fall. This way, your flower is all agile and in the best position to get transferred. 

After this, you can cater to the needs of your petunias from indoors. And as a house plant. Do this until spring, and you would have extended their lifespan.

Don’t forget that the maximum lifespan is around three years. So, no matter what you do, they’ll die naturally when this time elapses. 

Where Do Petunias Grow the Fastest?

Petunias grow fastest when the climate is warm, hot, and during summer. Petunias are from Argentina, and they grow best in conditions that are similar to that of Argentina. They grow fastest where the days are long and the evenings don’t experience frost.

Also, it’s best to grow in an area that allows the flower to access sunlight–a minimum of six hours. So, if you’re looking to grow your petunias fast, here’s the trick. Place them in an area that allows them to receive a substantial daily dose of sunshine.

Also, to get the best result, you’ll need a properly drained soil. So, if your area is made of clay, you’ll need to make some amendments. To do this, add various organic materials such as peat moss or compost. 

In Conclusion

Generally, petunia seeds germinate within a week, and they complete indoor growing between 10 and 12 weeks. Also, it might take as much as eight weeks for them to bloom.

However, you can easily speed up this process by getting a petunia for transplant. This way, you can save yourself 12 weeks of stress.

You might still want to grow petunias yourself and in record time. Then, you can go for pelleted seeds that are coated with materials. This way, you can increase germination speed by as much as 50%.

So, start planting and good luck!

Share on:

About Arindom Ghosh

A professional writer, editor, blogger, copywriter, and a member of the International Association of Professional Writers and Editors, New York. He has been part of many reputed domestic and global online magazines and publications. An avid reader and a nature lover by heart, when he is not working, he is probably exploring the secrets of life.