Winter:•For most plants, winter is a time of waiting.–When temperatures are below freezing, water is solid and cannot travel readily throughout the roots and stems.The lowest temperature that a plant can withstand is called its cold hardiness or cold tolerance.Plants that are able to survive temperatures lower than freezing are called frost-hardy.
–They vary widely in tolerance to subfreezing temperatures.Radiation frost - occurs when the air is cool and calm and skies are clear.When plants are covered by a barrier blocking flow of heat to the sky, frost can often be prevented is called Frost.Frost often leaves ice crystals on plants and the ground in the early morning, are called hoar frosts.–Called black frosts, because the first sign of their occurrence is the blackening of injured plants.Dew is most likely to occur when the air is warm and humid.–After sunset, air temperature drops, and the atmosphere is unable to contain the water it held during the daytime.•Water precipitates out, in the small droplets called dew.Humidity may determine how well a plant will grow.–Defined as the amount of water the air contains relativeto the amount it is capable of holding at that specific temperatureChanges in elevation can give areas only small distance apart completely different climates for plant growth.–The higher the elevation of an area, the colder the average year-round temperature•Every rise of 300 feet (91. 4 meters) causes an average temperature decrease of 1 deg. F.Changes in terrain alter climate, particularly rainfall.–Most rainstorms move from west to east in North America.–In a narrow range of hills, west-facing slopes often receive much more rainfall than east-facing slopes.•Heaviness of the water in rain clouds prevents them from passing over mountains until most of the precipitation hasbeen released.–The drier region on the eastern slopes often is referredto as a rain shadow.Microclimates are small areas with slightly different climate characteristics than the surrounding land.–May be less windy, shadier, moister, warmer, or in any other way different from the typical climate.•These differences affect plants, sometimes helping and sometimes hindering growth.A natural microclimate example is a frost pocket.–Colder, possibly moister due to water runoff.Desert plants (xerophytes) can protect themselves from excessive sun.
Heat tolerance rating of a plant in will soon be listed next to its USDA cold-hardiness number on care tags, in gardening references and in catalogs.•A plant will have two ranges.–For example: Lily 3–8, 8–1.•The first range (3–8) will designate the USDAlow-temperature hardiness by zone.–According to the lowest average temperature in winter.•The second (8–1) will designate heat tolerance.