The risk of frost

The riskt of frost creates many problems for us up here in the north, How frost affects nature creates many problems for us up here in the north, but if you are observant and a little prepared, milder frost can be managed reasonably well. First and foremost, you need to get to know the plants, the climate, and the microclimates so that you know where the risk of frost is most significant. Then several other factors make it easier to avoid frost.

Keeping track of the temperature

Checking the forecast for the night temperature is both simple and effective. If the prognosis says 3–4 degrees, there may be a local frost risk depending on how all the other factors affect you. The most significant risk of frost is at dawn.

Raised beds reduce the risk of frost precisely because they are raised. Stone and water absorb heat during the day, which is emitted during the night. Stone slabs or bricks around various perennial plants can help protect against frost, to name one example. Another easy and removable trick is to add water-filled milk cartons (those with screw caps) around sensitive plants. Heat is then built up during the day and delivered at night. If you want to put some extra work into this, you can paint the cartons a dark colour. It increases heat absorption, and the cartons become more beautiful. How long the heat lasts depends on how hot the day has been, how large the amount of stone/water is, how late at night the frost comes, and how long it lasts.

The heat loss at night is proportional to the sky’s surface to which an object is exposed. In order to understand this more easily, you can compare it to a mouse sitting in a cardboard tube on the ground, looking out into the night. The mouse sees only a small, small part of the sky, which means that it is not exposed to large amounts of cold air. On the other hand, if the mouse climbs out into the open, the exposure surface is the entire sky, which means that the mouse must handle a much higher degree of chilly weather. This difference is why you should crawl under a large tree – preferably spruce – if you have gotten lost and need to stay the night in the forest.

Clouds provide a lower risk of frost

A starry night sky quickly releases the heat of the day, while clouds effectively stop the earth’s heat radiation. Therefore, the risk of night frost is much smaller on a cloudy night.

The wind can both increase and decrease the risk of frost

How frost affects nature is depending on the strength of the wind. Most people know that the risk of frost increases if there is no wind, but just because there is wind does not automatically mean that the danger has passed. In order for the wind to protect against frost, there must exist mild winds that cause different air temperatures to mix with each other. If you have too much wind, the frost’s risk increases as the warm air blows away, leaving room for the denser cold air to drop to the ground.

Cold air travels down

If your crops and gardens are on hilly terrain, it is crucial to remember that cold air drops and warm air rises. When the temperature falls at night, the cold air slides down the slope and lays as a lid over the lowest area. At the same time, the warm air rises along the slope. This effect applies both on large and small scales. As stated before, even the tiniest little dip can suffer frost due to this.

The length of the night determines the risk of frost

The longer the night lasts, the longer the heat has to flow out into space, and with that increasing the risk of frost. This is part of the explanation why there are frosty nights in the early summer and early fall, but not in the middle of summer.

Irrigation against frost

The so-called dew point is the temperature at which the air can no longer retain the air’s moisture. This phenomenon can be used as frost protection due to when moisture condenses; it creates heat, which helps keep the frost away.

Therefore, a light watering one or two days before there is a risk of frost can help to keep the frost at bay. Only a light watering, mind – as a more substantial amount of water in the soil can instead increase the risk.

In larger ventures, it is common to use irrigation to prevent crops from freezing. By placing a thermometer about one meter above the plants and hooking up a simple alarm that is connected to the thermometer, one can quickly know when it is time to go out and turn on the water.

Trees protect against frost

The heat that the trees store during the day protects the immediate surroundings from frost. Also, the trees’ perspiration protects due to the air’s moisture content increasing, thus increasing the heat. One way to take advantage of this is to grow around and in the vicinity of, for example, fruit trees.