Petunia Cold Tolerance
Petunias prefer nighttime temperatures between 57 and 65 degrees F. (14-16 C.) and daytime temps between 61 and 75 degrees F. (16-18 C.). However, petunias usually tolerate temperatures as low as 39 degrees F. (4 C.) with no problem, but they are definitely not plants that will survive the winter in most climates. Petunias are damaged extensively at 32 degrees F. (0 C.), and killed very quickly by a hard freeze.
Extending Petunia Cold Hardiness
You may be able to extend the life of petunias for a short time when temperatures begin to drop in autumn by protecting the plants. For example, cover petunias loosely with an old sheet in the evening, then remove the sheet as soon as the temperature moderates in the morning. If it’s windy, be sure to anchor the sheet with rocks or bricks. Don’t use plastic, which offers very little protection and can damage the plant when moisture collects inside the plastic. If your petunias are in pots, move them to a sheltered location when cold weather is predicted.
New Frost Tolerant Petunias
Petunia ‘Below Zero’ is a frost-hardy petunia that has been in development for several years. The grower claims that the petunia can tolerate temperatures down to 14 degrees F. (-10 C.). Reportedly, this bushy petunia will survive through winter frost and snow to bloom with pansies and primroses in early spring. However, this petunia may not yet be available at your local garden center. To err on the side of safety, it’s probably better to grow these flowers as annuals each year or you can try overwintering the plant indoors – even taking cuttings from plants to make new ones for next season.
