What species?

I have salvia microphylla, greggii, maraschino, and Black & Blue.

I've left these outside with temps as low as 25 degrees during predawn hours without harm. Please note that temps continue to drop until the sun comes over the horizon, including the tops of trees and other local high objects. It takes direct sunlight to reverse the drop in temperature.

They should all be ok with a light freeze, but if they are in pots, do make sure that they will not get waterlogged.

The only one of those I've had in a pot was the "Black and Blue" (since planted in the ground). It made it through our very cold January last year - at least a week of low 20s, dying back to the surface and returning in late winter/spring, as per usual.

Brenda

My greggi and microphylla suffer flower damage at temperatures around freezing and slightly below, but they quickly recover if the weather moderates. Eventually, once the weather settles to below freezing every night their foliage dies back and they go dormant. In the worst winters, well most winters, they die to near the ground and don't begin to come alive until late April. Maraschino seems exceptionally hardy, reliably keeping green wood 3 and sometime 4 feet up the stem even in the worst of winters. Temperatures here can go to nearly zero around here. I used to hope the plants wouldn't die back to near the ground every winter, but I've changed my tune. The plants that sprout from near the ground have much better structure, and retain their shape longer. Maraschino in particular wants to become a big flopping monster and needs a strong hand.

The only thing I might add is to pull the pots as close to the house as you can, the radiant heat form the walls' heat-mass will keep the temps a bit higher.

Thanks for all your comments. The weather reports are forecasting mid 30's beginning tomorrow night. I will move the pots close to the house and cover them with plastic if possible.

I would not expect any damage if the temperature of the plants drops only to the mid thirties (a few degrees above freezing, for you metric system readers). However, it is possible to have frost at plant level even when air temps are above freezing. A light frost would likely burn a few flowers, perhaps slightly burn the leaves of some of your salvias - black and blue is probably the most frost tender of the group you listed. However, damage should be minor, and any overhanging roof or leafy trees should be enough to prevent frost formation unless the air temp gets down to freezing.