Protecting Plants from Cold

The last frost in the spring and the first frost in the fall are likely to be radiation frosts. Radiation frosts occur on clear, still nights as the heat of the soil is radiated to the dark sky. Either wind or a cloud layer will usually prevent a radiation frost. A clearing night following a day of rain is especially likely to engender the first frost of the fall.

If you can protect tender plants against this first frost, you may get another week or two of growth from them. The easiest protection against a radiation frost is a covering. An old sheet or a piece of cardboard is often all that is needed. Plants in containers can be moved under the eaves, which will offer them enough protection.

Another technique for preventing frost damage is to employ heat sources. Many small heat sources are more effective than a single large one. Use charcoal, jellied alcohol, heater cables, or electric lights. For home gardeners, a simple and practical solution involves using heater cables or a single incandescent electric bulb at the base of favorite plants, with the plant covered by plastic.

Watering adequately helps protect a plant during frost and cold. If a plant has adequate soil moisture to replace moisture transpired through its leaves, the plant will be less likely to suffer damage. In hard-freeze regions, water the garden until the ground freezes. After the ground freezes, mulch plants so that frost will not penetrate deeply into the ground. Use mulches of chopped leaves, wood chips, straw, evergreen boughs, and pine needles. Watering and mulching can reduce the desiccating damage caused by winter winds drawing water from leaves, warm sun stimulating leaves to transpire, and frozen soil withholding its water (as ice) from the roots.

Periodic thawing and freezing of the soil can heave small plants out of the ground. Once frozen, it’s better if a plant stays frozen until spring. Alternate freezing and thawing of water-filled cells causes cells to burst.

Tree bark sometimes suffers injury, splitting vertically, when sun warms the tree cells on the outside. The warm cells then refreeze quickly, causing tension between the outer and inner bark that splits the tree.