Whether they’re charming, compact millifloras in pastel shades, spreading varieties that cascade over a hill, or grandifloras with three-inch blooms in bold purple, all Petunia species belong to the nightshade family and are native to South America, in regions with hot and humid weather.
While you’ll find more selections of the modern hybrid varieties than ever before, all petunias still share this “warm weather preferred” trait.
They will not tolerate frost – at least not more than a touch of it. And they’re not cold hardy.
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These tender perennials are able to survive outdoors in winter only in warm-weather USDA Hardiness Zones 9 to 11, coming back year after year with proper care.
Gardeners in other areas must satisfy themselves with growing petunias outdoors as annuals.
There’s more to it than that, though.
Even if your flowers can’t endure once freezing weather sets in, you can prepare them to bloom well after chilly temps first arrive, and make preparations all summer to make sure they’ll stay alive as long as possible.
Here, I’ll give a few pointers for those growing perennial petunias in more temperate zones.
I’ll also share my tips for those in cooler areas who want to encourage petunias grown as annuals to flower for as long as possible into the fall.
Here’s what I’ll cover:
Petunia Cold ToleranceHere’s the big picture on this flower’s cold hardiness:
Petunias thrive when nighttime temperatures are in the 55 to 65°F range, and daytime temps are between 61 and 80°F.
They will succumb to sub-freezing temperatures in a hurry, and anything below 40°F may kill
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