For many herb gardeners, there is a fine line between too little or too much water.
This is true in the winter, even when your herb garden lies dormant. If you garden where winters are cold, a big threat to your plants is frost heaving.
Heaving occurs when the ground (and your herbs) go through freeze and thaw cycles.
Moisture in the ground freezes turning to ice, and the ice contracts and expands with each freeze and melt cycle.
Often this cycle will cause herbs, garden plants, and even concrete to heave up out of the ground. This heaving affects your herbs and plants by exposing roots to harsh winter winds and weather.
Without the soil’s protection these exposed roots can be injured or die off… killing the plant.
Frost heaving during the winter not a big problem for herb gardeners that have frozen temperatures and deep snow all winter, but heaving can still occur for them in the Spring when temperatures fluctuate and melting snow adds lots of extra moisture to the soil.
If frost heaving is an issue in your herb garden, you can protect or insulate your plant roots with a deep mulch, leaves or even cover individual favorites with rose cones. There is no guarantee that your plants won’t suffer damage, but mulching or covering roots may help more of your herbs to survive!
Source: Gardening101