• Frost is water vapor, or water in gas form, that becomes solid. Frost usually forms on objects like cars, windows, and plants that are outside in air that is saturated, or filled, with moisture. Areas that have a lot of fog often have heavy frosts.

    Frost forms when an outside surface cools past the dew point. The dew point is the point where the air gets so cold, the water vapor in the atmosphere turns into liquid. This liquid freezes. If it gets cold enough, little bits of ice, or frost, form. The ice is arranged in the form of ice crystals.

    Frost is most common in low-lying areas. Warm air rises, and cool air sinks—cool air is denser than warm air. That means there are usually more water molecules in cool air than in warm air. As cool air collects in valleys, frost forms.

    Frost usually forms at night, when the air temperature is cooler. Once the sun rises and warms the air around the frosted object, frost melts quickly.

    Types of Frost

    There are different types of frost. The most common are radiation frost (also called hoarfrost), advection frost, window frost, and rime.

    Radiation frost is frost in the form of tiny ice crystals that usually shows up on the ground or exposed objects outside. Hoarfrost also forms in refrigerators and freezers.

    Advection frost is a collection of small ice spikes. Advection frost forms when a cold wind blows over the branches of trees, poles, and other surfaces.

    Window frost forms when a glass window is exposed to cold air outside and moist air inside. Window frost is familiar to winter residents of cold climates. Indoor heat and cold outdoor temperatures form this type of frost. Window frost was much more common before people began using double-paned windows.

    Rime is frost that forms quickly, usually in very cold, wet climates. Rime also forms in windy weather. Rime sometimes looks like solid ice. Ships traveling through cold places like the Arctic Ocean often end up with rime covering at least part of the exposed part of the ship.

    Frost and People

    Frost can severely damage crops. It can destroy plants or fruits. Plants with thin skins, such as tomatoes, soy, or zucchini, can be ruined. If frost is bad enough, potatoes will freeze in the ground. Farmers have had entire fields destroyed in just a few frosty nights.

    Farmers typically consult almanacs and maps to predict frost. Maps and information from almanacs (such as previous days of frost) tell farmers what areas usually receive frost, how often it occurs, and how long it lasts. These tools are reliable but are not always accurate.

    Although farmers still rely on the weather, many spray their crops to reduce frost damage. This spray usually contains a genetically modified organism (GMO), an organism whose genes have been altered by people. The GMO that reduces frost damage to crops is called ice-minus bacteria. Ice-minus bacteria make it difficult for ice crystals to form. Ice-minus bacteria do no damage to the plant.

    Many farmers also protect their crops by using the selective inverted sink (SIS) method. The selective inverted sink is a large fan that draws cold, moist air up into a chimney. The chimney expels the cold air far above the crops. This protects crops from frost without spraying them.

    Sturdier plants are not destroyed by frost, but frost will stop them from growing. Evergreen trees, such as pine and spruce, will stop growing during a frost, but they won't die.

    Roads can also be damaged by frost. Frosty roads are slippery and, exposed to the heat from cars, quickly become wet. Many drivers have trouble navigating frosty or wet roads.

    Hardy plants can withstand frost.

    Don't Give These to Your Girlfriend
    Frost flowers are formed when water in plant stems or trees oozes and freezes, sometimes in the shape of a flower. These types of "flowers" are rare, and when they do form, they're destroyed easily because they're so delicate.

    Rime of the Ancient Mariner
    The English poet Samuel Taylor Coleridge wrote a famous poem called The Rime of the Ancient Mariner, published in 1798. In the poem, an old sailor tells the story of how his ship lost its way in a storm, eventually ending up in the Antarctic. Coleridges title is a play on words. Much of the story takes place in the Antarctic, on a ship that is covered with rime. The mariners long, white beard is compared to hoarfrost. Finally, The Rime of the Ancient Mariner is written in rhyme.

    Father Frost
    The Russian Santa Claus is named Ded Moroz, or Father Frost.

  • Term Part of Speech Definition Encyclopedic Entry
    accurate Adjective


    advection frost Noun

    ice crystals shaped like spikes that form from a cold wind.

    air Noun

    layer of gases surrounding Earth.

    Encyclopedic Entry: air
    almanac Noun

    annual publication containing a calendar, astronomical information, and weather forecasts.

    Antarctic Noun

    region at Earth's extreme south, encompassed by the Antarctic Circle.

    Arctic Ocean Noun

    one of Earth's four oceans, bordered by Asia, Europe, and North America.

    climate Noun

    all weather conditions for a given location over a period of time.

    Encyclopedic Entry: climate
    crop Noun

    agricultural produce.

    Encyclopedic Entry: crop
    delicate Adjective

    fragile or easily damaged.

    dense Adjective

    having parts or molecules that are packed closely together.

    dew point Noun

    temperature at which water in the air condenses to form water droplets on objects near the ground.

    evergreen Noun

    tree that does not lose its leaves.

    expel Verb

    to eject or force out.

    farmer Noun

    person who cultivates land and raises crops.

    fog Noun

    clouds at ground level.

    Encyclopedic Entry: fog
    freeze Noun

    weather pattern of temperatures below 0 degrees Celsius (32 degrees Fahrenheit).

    frost Noun

    thin coat of ice covering objects when the dew point is below freezing.

    Encyclopedic Entry: frost
    frost flower Noun

    ice crystals that form from moisture released by a plant stem or tree.

    fruit Noun

    edible part of a plant that grows from a flower.

    gas Noun

    state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

    gene Noun

    part of DNA that is the basic unit of heredity.

    genetically modified organism (GMO) Noun

    living thing whose genes (DNA) have been altered for a specific purpose.

    glass Noun

    brittle, transparent substance made from melted and fused minerals such as silica.

    hoarfrost Noun

    ice crystals that form as water vapor near objects becomes solid. Also called radiation frost.

    ice Noun

    water in its solid form.

    Encyclopedic Entry: ice
    ice crystal Noun

    solid ice arranged in precise molecular form.

    ice-minus bacteria Noun

    organism that makes it difficult for frost to form.

    map Noun

    symbolic representation of selected characteristics of a place, usually drawn on a flat surface.

    Encyclopedic Entry: map
    moisture Noun


    molecule Noun

    smallest physical unit of a substance, consisting of two or more atoms linked together.

    mountain Noun

    landmass that forms as tectonic plates interact with each other.

    pane Noun

    sheet of glass or other material placed in a frame for a window.

    pine Noun

    type of evergreen tree with needle-shaped leaves.

    potato Noun

    plant native to the Americas.

    predict Verb

    to know the outcome of a situation in advance.

    radiation frost Noun

    ice crystals that form as water vapor near objects becomes solid. Also called hoarfrost.

    refrigerator Noun

    space with artificially lowered temperature.

    reliable Adjective

    dependable or consistent.

    rhyme Noun

    word that has the same ending sound as another word.

    rime Noun

    ice crystals that form in wet, windy conditions.

    sailor Noun

    person who works aboard a ship.

    Samuel Taylor Coleridge Noun

    (1772-1834) English poet.

    saturate Verb

    to fill one substance with as much of another substance as it can take.

    selective inverted sink (SIS) Noun

    method of preventing or reducing frost damage to crops by fanning cold, moist air up a chimney.

    soy Noun

    beans, or fruit, of the soybean plant, native to Asia.

    spruce Noun

    coniferous, or cone-bearing, tree.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    tomato Noun

    plant and fruit native to the Americas. Also considered a vegetable.

    vapor Noun

    visible liquid suspended in the air, such as fog.

    weather Noun

    state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

    Encyclopedic Entry: weather
    wind Noun

    movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.

    window frost Noun

    ice crystals that form when a window is exposed to freezing temperatures on one side and moist air on the other.

    zucchini Noun

    type of vegetable (squash). Also called a courgette.