Freezing is destructive to crops. One reason it is dangerous to crops is because water expands as it freezes. The freezing then unthawing of a crop can damage its structure and cause it to die. To avoid these risks, crops are planted and harvested at times of the year when freezes generally do not occur. However, freezes that are unusually late, early or a freeze at a location that does not typically experience freezes can cause serious damage to crops. This writing goes over techniques that are used to reduce the threats from freezes. Covering of plants: Covering plants helps hold some of the daytime heat between the soil and the air around the plants. This can be effective in small gardens. It is not practical for crops that cover a large area. This works well for greenhouses since temperatures in the greenhouse will be warmer since it acts like a large cover. Spraying with water: Spraying with water can help keep the temperature just above freezing since the warmth of the water adds heat energy and when the water tries to freeze it releases latent heat energy that keeps the temperature from dropping below freezing within a crop. The water surrounding the crop will freeze first and this can save freezing damage from occurring within a fruit or vegetation. This method is effective if the wind is light and the temperature is near freezing. If the air temperature is expected to drop well below freezing then this method will not work. Fans: Fans are particularly effective in situations in which the overnight cooling results from radiational cooling. In these cases the coldest air will be very shallow at the surface. The fans will help mix warmer air higher up with the coldest air at the ground surface. Fans work best for situations in which the temperature is expected to be near freezing. They are not as practical when the temperature drops well below freezing. Heaters: This can be a set up a several small heaters that are evenly spaced out within the crops. This can add just enough heat to prevent the temperature from causing freeze damage to the crops. It can be expensive though due to the energy that is needed. |