Many food and ornamental plants are native to warm climates and can’t withstand freezing temperatures. Others go dormant for winter. Thus, the primary growing season for most North American gardeners is between the last frost in spring and the first killing frost
Air temperature is only one of the factors that determine whether or not plants will be damaged by a frost. Sometimes when the temperature dips a little below freezing, the air is sufficiently moist for water vapor to condense (in the form of ice crystals) on the ground and on plants. When water condenses, it gives off heat and warms the air around plants, protecting them from extensive damage. On clear, windless, star-filled nights when the forecast calls for near-or below-freezing temperatures, it’s wise to protect plants. Heat is lost rapidly under these conditions, and frost damage often occurs. When temperatures fall more than a few degrees below freezing, frost damage to growing leaves and shoots is likely no matter how humid conditions are.
Frost damages plants when the water in the plant’s cells freezes and ruptures the cell walls. Different plants and parts of plants have different freezing points. Plants that are native to Northern regions have many ways of protecting themselves from the cold. Many perennials die down each fall. The roots buried in the insulating soil remain alive to sprout again the next season. Some plants such as kale have cold-tolerant leaves that will survive unharmed under a blanket of snow, but not when exposed to drying winds. Deciduous shrubs and trees drop their leaves each fall and form leaf and flower buds that stay tightly wrapped in many layers and go dormant until spring comes again. Or, like cold-hardy evergreens, they may have a natural antifreeze in their sap that helps prevent them from cold injury.
Using a Rain Gauge
Natural rainfall is an important factor in which crops you can grow and how to take care of those you do grow. Keep track of the rainfall in your garden with a rain gauge. You can buy a gauge, or simply use an empty tin can and a ruler. An inch of rain in the can equals an inch of rain on the garden.
Frost heaving of soil
can also cause problems for gardeners. Soil moves as it freezes, thaws, and refreezes. This action can push newly planted perennials, shrubs, or other plants that don’t have established root systems out of the soil. Mulch
heavily around these plants after (not before) the soil freezes to prevent thawing during sudden warm spells in winter or early spring.