How Fast Do Petunias Grow?

How Fast Do Petunias Grow?If you love that gorgeous fresh color that petunias can add to any garden, you may be wondernig - just how long would it take you to achieve the same look in yours? Once you seed or plant them  - how long does it take to grow petunias and enjoy that wonderful array of colorful blooms?

Petunia seeds will germinate within one week if they are sown in ¼ deep potting soil that is both moist and fertilized. The soil temperature should be between 65 and 75 degrees Fahrenheit for optimum germination. The plants will grow fairly quickly if the proper growing conditions are met and should produce flower buds in as little as 6 to 8 weeks. Expect plants to take 10 to 12 weeks from seed sowing to flowering.

Now that you know the rate at which petunias grow, let’s take a look at this in more detail below. We will discuss how long it takes for petunias to grow from seeds as opposed to transplants. We will also explore the time it takes for the plant to bloom, what effect temperature has on their rate of growth, how long petunias last and whether or not they grow back each year.

So, if you’re ready to learn more about how long it takes to grow petunias, then let’s get started!

How Quickly Do Petunias Grow?

Petunias are a very popular flower that originated in Argentina, South America. There are many different types of petunias (over 35 known species) that come in a variety of colors, patterns, and sizes. They fill in space around plants in a garden and look beautiful against a backdrop of green foliage.

The speed at which you can get to that burst of color depends on how you grow them. Growing petunias from seed as opposed to transplants takes much longer, with more care and effort required.

Growing Petunias from Seeds

Petunia flowers young seedling sprouts from seeds

It takes approximately 7 to 10 days for petunia seeds to germinate, begin to grow and sprout. This is quite slow by growing standards. Begin indoors in late winter and sow petunia seeds in moist, fertile soil for about 10 to 12 weeks before the intended outdoor planting date in the spring.

To maintain consistent moisture levels, place a clear plastic dome,  or some plastic wrap, over the planter or pot. Do not set the pot in direct sunlight at this time. The intense heat could inhibit or even prevent germination.

As soon as germinations occur, remove the dome or plastic wrap. Place the seedlings in a sunny window or under fluorescent lighting. Make sure the fluorescent lights are at least 4 to 6 inches above the plants and left on for 12 to 16 hours daily.

Growing Petunias from Transplants

Petunia transplants are easier to grow than petunia seeds with less time and effort on your part. You do not need to start them indoors and cuttings can be planted directly into a pot, hanging basket or garden bed immediately after purchasing. This saves you approximately 10 to 12 weeks of growing time.

Do Pelleted Petunia Seeds Grow Faster?

Pelleted seeds are seeds that are coated with a material to make them larger and easier to handle. Germination time can be up to 50 percent faster with pelleted (or primed) petunia seeds. The only downside is that they do not have the same storage life as unprimed seeds.

How Long Does it Take for Petunia Seeds to Grow?

Germination takes anywhere from 5 to 15 days for petunias that start indoors at average room temperature, which is 68 to 72 degrees Fahrenheit. If you are lucky enough to have a greenhouse and can keep them in a slightly warmer temperature (75 to 85 degrees Fahrenheit), they will germinate in as little as 3 or 4 days.

How Long Before Petunias Bloom?

Petunia seeds are very small and need a lot of light to germinate. They take anywhere from 6 to 8 weeks to flower. You should start them indoors in moist, fertilized soil and then move them outside after 10 to 12 weeks. Do not place them outdoors until the plants have a least 3 leaves. It is often easier and quicker to grow them from transplants.

Does Temperature Affect the Growth Rate of Petunias?

Blooming petunia on summer

As the temperature rises, plants will grow faster. This goes for petunias as well. For the quickest flowering of petunias, they must be in areas with warm temperatures (65 to 75 degrees Fahrenheit) and long days with up to 16 hours of sunlight.

If petunias are planted in cooler temperatures (less than 65 degrees Fahrenheit), longer days will have less of an effect on their growth. They need heat to survive and to thrive. Therefore, if petunias are grown in very warm regions where the temperature reaches 75 degrees or higher consistently, they will continue to grow even in shorter days with 8 hours of sunlight or less, but not as well.

Where Do Petunias Grow the Fastest?

Petunias will grow the fastest in regions with warmer climates and hot, humid summers that are similar to Argentina, their place of origin. Long days and mild evenings (free of frost) provide the fastest growing conditions for these flowers.

How Long Do Petunias Last?

Petunias are perennials in warmer climates. They typically bloom during spring and summer, die back in autumn or winter and return again the following spring. Petunias have a natural limit to their lifespan and will eventually die back for good after 3 or 4 years. In cooler climates, they grow as annuals.

In regions where the climate is warm year-round, they often continue to bloom throughout the autumn and early winter months. It is usually recommended to keep petunias indoors during the winter if you want them to return again in the spring. Rarely will a petunia grow longer than 12 to 18 months.

Do Petunias Grow Back Every Year?

Petunias are often considered half-hardy annuals, even though they are actually perennials. They will usually survive the first frost, as long as it is light. They will not, however, survive a heavy frost and once frozen will die. Frost-injured plants can be cut back and what remains should outgrow the damage, thus allowing the plant to return again the following spring.


In summation, petunia seeds will germinate within one week, if they are sown in ¼ deep potting soil that is both moist and fertilized. The warmer the temperature, the quicker the petunias will grow. Therefore, soil temperature must be between 65 and 75 degrees Fahrenheit for optimal germination to occur.

If the proper growing conditions are met, the petunia plants should produce flower buds in as little as 6 to 8 weeks. It takes 10 to 12 weeks of indoor growing before petunias can be planted outside. Good luck and happy gardening!

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