Bare Frost

Bare frost refers to periods of frost when the ground is frozen but there is no protective snow cover. The term "bare" points to the absence of the insulating snow that normally shields plants from extreme temperature swings.

During bare frost, the ground freezes deeply and evenly. This weather is particularly dangerous for plants with sensitive roots or above-ground parts, as they're left exposed to cold, dry air. Evergreen plants also suffer, because they lose water through their leaves but can't take any up from the frozen ground – this can lead to winter desiccation.

Plants at Risk

Bare frost is particularly harmful to:

Evergreen shrubs such as box, cherry laurel and rhododendron
Evergreen perennials and grasses
Shallow-rooted ornamentals and young plants
Vulnerable container plants without insulated pot protection

Effects and Damage

Frozen ground prevents water uptake, causing plants to dry out. Frost heave can also occur, where the cracking soil lifts roots to the surface, exposing them to freezing. Larger temperature swings can also cause splits in the bark or plant tissue.

Prevention and Protection

Good preparation helps avoid bare frost damage:

Cover the soil with mulch, leaves or brushwood to buffer temperature swings.
Position evergreen plants in sheltered spots, away from wind.
During frost-free spells in winter, water occasionally to prevent drought stress.
Insulate container plants or overwinter them somewhere frost-free.
Protect vulnerable plants from wind and cold with fleece or hessian sacking.

An unbroken layer of snow is the best natural protection against bare frost, as it acts like an insulating blanket, keeping soil and roots at an even temperature.