Placea 2-inch layer of mulch around vulnerable plants (blooming plants, plants with new growth, less hardy plants) to hold heat in the soil and help protect the roots.
Water the soil heavily (to a depth of about 6-7 inches) during daytime hours. Counterintuitively wet soil holds more heat than dry soil to help protect plants, but avoid getting water on the plants.
Cover plants with bedsheets overnight. Place upright sticks or stacks around the plants to prop up the sheets to avoid crushing the plants. Remove the sheets the next morning after the sun is up and the temperature is above 40 degrees.
Prune frost-damaged plants once there is no longer a risk of frost since new growth is especially susceptible to frost.