If hobby gardeners are surprised by the bare frost, it is important to act quickly. You can still prevent major damage to your garden plants with these measures.
In the case of evergreens such as rhododendrons, bare frost causes the leaves to gradually dry out, as frozen roots and branches can no longer transport water to them
Meteorologists speak of frost when deep sub-zero temperatures fall on a "bare" ground, so do not hit the ground covered with snow. Bare frost usually occurs in Germany whenever there is a stable continental high-pressure area over Eastern and Central Europe in winter. This weather situation is often associated with cold winds from the east, which bring very dry Siberian cold air with them.
Bare frost is critical for many garden plants, because the snow cover as a natural insulating layer is missing. The frost can therefore penetrate unhindered into the soil and let it freeze through particularly quickly and deeply. At the same time, with a high pressure influence, the sky is usually almost cloudless and the sun, which is already quite warm from mid-February, warms the above-ground parts of the plant. The leaves of evergreen woody plants, such as cherry laurel or boxwood, thaw quickly after the night frosts and are stimulated to transpiration. They lose water and dry out over time, because no water can flow from the frozen roots and thicker branches. Cold, dry easterly winds exacerbate this effect, known in gardening parlance as frost dryness.
Shading and wind protection for evergreen deciduous shrubs
But what is the most effective way to protect your plants from frost damage during a bare frost?? This depends primarily on which plants are concerned. The most effective protection for evergreen deciduous shrubs such as rhododendrons is a winter fleece, in which the entire crown is best wrapped. If the plants already have a location that is semi-shaded and protected from the wind even in winter, on the other hand, you can usually do without this measure.
Mound roses at the base – the rest will grow back
If there is a threat of bare frost, the sensitive base of roses should be protected with heaped humus soil and fir brushwood
Roses are not evergreen, but the shoots and grafting site are still often damaged by frost. Particularly treacherous are late frosts, which occur only when the shoots are already in the sap, i.e. are about to sprout new shoots. For bedding roses, it is especially important that the shoot base is well protected from damage, since the old flower shoots are cut back severely in the spring anyway. Experienced rose gardeners even claim that the rose blossoms are always particularly lush when the shoots have frozen far back in winter. You can effectively protect the sensitive base of the shrub by mounding it with humus soil or autumn leaves, which you can then stabilize with fir twigs.
Alpine rock garden plants are sensitive to frost!
Hardly any hobby gardener wastes a thought on winter protection for his rock garden – after all, most of the species that grow here come from the high mountains, where it freezes stone and bone in winter. But: Here there is usually no bare frost, because it also snows a lot in winter, and the snow acts as a natural winter protection. For this reason, you are well advised to completely cover your rock garden with a winter fleece or fir brushwood when a bare frost occurs.