With their vibrant blossoms and gorgeous look, petunias can add an out-of-world beauty touch to your garden.
But this is only possible if you provide it with the proper lighting. This is what I’ll guide you through here.
In this post, I’ll provide you with all you need to know about the lighting needs of petunias from seed to full-grown.
What Are the Lighting Needs of Petunias?
Here’s the thing: all petunia species require plenty of sunlight exposure every day. You need to provide them with a minimum of six hours of daily sunlight.
Still, to enjoy their best look and the maximum number of flowers, ensure they receive eight hours or more of sunlight per day.
In case petunias don’t receive enough sunlight, they’ll produce considerably fewer blossoms and will likely grow shorter.
Even worse, if they receive five hours or less sunlight daily, these plants won’t produce any flowers at all.
How Does Climate Impact the Lighting Needs of Petunias?
Generally, you can plant petunias in hardiness zones 2 to 11. The climate in your area impacts how much sunlight your petunias need.
In warm climates such as Florida, petunias can thrive with relatively less sunlight exposure than in a cold climate area like Minnesota. This is due to the high intensity of sunlight in warm areas.
The climate also affects the blooming time of the plant. Petunias are perennials in warmer areas like zones 10 and 11, So they can bloom all year round.
Conversely, in other zones, the plant is annual and blooms only from the planting time to the first frost in fall.
Do Petunias Need Full Sun?
Ideally, you should grow your petunia plants where they receive full sunlight. This is especially helpful in cold climates.
The more sunlight petunias receive, the more flowers they will produce.
Sunlight also significantly impacts the size of the plant itself. For example, cascading varieties will reach an incredible size when planted in full sun.
Some might even grow to cover up to 10 square feet when they receive the perfect sun exposure and care.
Can Petunias Get Too Much Sunlight?
The petunia plant is one of the most sunlight-tolerant out there. It won’t have any problems staying all day under direct sunlight if the temperature is below 90 °F.
In fact, the more they get exposed to sunlight, the healthier and more beautiful they become.
Nonetheless, if the sun’s heat temperature is above 90 °F, this can harm your petunias if they are exposed to it for several hours. Extreme heat can lead petunias to dry out and turn their leaves brown.
So, if you’re living in a hot climate, I recommend growing your plant in a place where it receives only the morning sunlight.
In the afternoon, you’ll need to create a partial shade around the plant to limit the heat it receives. You can use umbrellas or shade cloths to create this portal shade.
Can Petunias Grow in the Shade?
Whether your petunias can grow in the shade depends on whether it’s partial or full. It’s highly probable for petunias to survive in partial shade; however, the same isn’t true for full shade.
Let’s see the impact of partial shade vs. full shade on the growth of your petunias:
Partial Shade
Petunias can survive when planted in an area with partial shade, yet this isn’t their ideal condition.
In partial shade, the plant produces fewer blossoms compared to when it receives full sun.
This can also cause plants to become spindly. In this case, you may need to prune the spindly or weak stems and leaves. Pruning can stimulate new health growth and help produce more flowers.
Overall, unless you live in an area with a sweltering climate, I highly recommend you provide your petunias with full sun.
Full Shade
Planting petunias in full shade will severely impact their growth and cause them to become weak and thin.
Over time, they won’t likely survive even if you provide them with the ideal watering and nutrient requirements.
Can Petunias Grow in Indirect Sunlight?
Petunias can survive in indirect sunlight, but it’s not optimal for them. When receiving only indirect sunlight, petunias produce fewer flowers compared to direct sunlight.
So, I don’t recommend growing them in a location with indirect sunlight unless you have to do so.
In this case, try to increase the plant’s exposure to the sun to 8 or 10 hours. You can use growers’ light to complement the indirect sunlight as well.
Can You Grow Petunias Indoors?
Yes, you can. A sun-loving plant like petunia will be in its best condition when it grows outdoors. However, you can grow it indoors if you provide it with the right conditions.
Here’s how: place your petunias in a well-lit and well-vented space. Keep them as close as possible to a south-facing window to give them six hours of daily sunlight.
You’ll also need to turn the plant every couple of days to ensure that every part of it receives sufficient sunlight.
Because your indoor petunias will likely receive only partial sunlight, you should provide them with grower’s lights. This is to increase the overall amount of light they get daily.
Can Petunias Grow in Artificial Light?
Yes, you can grow your indoor petunia plants in an artificial light if the natural sunlight is insufficient. Many people have succeeded in doing so.
A 2016 study examined the effectiveness of various light sources on petunia growth.
They tested LED lights and how they impact the flowering of petunias and found that they can be a decent alternative to natural light.
However, the study reported that different types of artificial lighting triggered different responses from the plant.
For example, red and blue LED light cause petunias to assimilate higher amounts of CO2 compared to plants that grow in white LED light.
Do Petunia Seeds Need Light?
Yes, petunia seeds require light to germinate as they’re photosensitive. For this reason, you should surface-sown them instead of covering them with soil.
The best way to do it is to just press the seeds lightly into the ground medium. Then, place them in a location with proper light and warmth.
These seeds take from 5 to 15 days to germinate. You should ensure they receive 12-16 hours of light a day throughout this period. Place them in indirect sunlight as direct rays might harm them.
Of course, you can supplement the natural light with artificial lighting if you’re in a place with relatively short daytime.
When the seeds germinate, you need to place seedlings in a spot with fluorescent light for 12 hours a day to maintain their healthy growth.
Final Thoughts
Petunias require ample sunlight exposure to thrive. They will grow healthy with six hours of daily sunlight or more.
However, to reach their most vibrant flowers and beautiful look, you should provide them with over eight hours of sunlight daily.
That’s why I recommend providing your petunias with full sun as long as the temperature is 90 °F or below.
If the temperature exceeds this degree, I recommend avoiding the afternoon sweltering sun by creating a shade on the plant at that time. In this case, only rely on the morning sun as the direct light source of the plant.
With the proper lighting and care, you’ll enjoy the gorgeous flowers of petunias. Happy gardening!
Growing up with a mom who filled her home (inside and out) with all sorts of plants, Lisa got her start in gardening at a young age. Living now on her own with a home and yard full of plants (including an indoor greenhouse), she shares all the gardening tips she’s gained over the years.