It may seem counter-intuitive, but one strategy that commercial growers use to protect plants from cold temperatures is to water the soil prior to a frost. Water is an excellent insulator. Plant cells that are plump with water are more resistant to frost damage. Moist soil retains heat better than dry soil and conducts more warmth to the surface, warming the air above moist soil by as much as 5 degrees F higher than the air above dry soil. Regular watering during periods of dry, cold weather can help protect plants from freezing temperatures. If your area experiences rainy winters and plants are at risk of over-watering, water thoroughly early in the day before a hard frost is predicted. It is not recommended to water if snow or ice is on the ground. So, if your soil remains frozen all winter long, water everything well during the fall while temperatures remain above 40 degrees F.
Understanding Frost by Cornell Cooperative Extension, Chemung County
When to Water Plants Before a Freeze by Julie Day, Today’s Homeowner with Danny Lipford