Frost Management

Cranberries, like many other temperate crops, are sensitive to below-freezing temperatures during the active growing season. This sensitivity is an important factor in cranberry management. Cranberry bogs have traditionally been placed in lowland areas such as swamps and marshes, compounding frost concerns since the temperatures on cranberry bogs tend to be lower than those in surrounding lands. In recent years bogs have also been constructed in upland areas on mineral soils. However, all bogs are constructed with the planted area at a lower level than its adjacent surroundings. This arrangement contributes to the development of ‘frost pockets’ on the bogs. The cold air drains from the adjacent high ground into the low areas on clear, calm nights. In addition, the enormous amount of vegetation present on a cranberry bog is extremely efficient at radiating heat under clear, calm skies, a process known as radiational cooling. Due to these factors, it is not unusual for bog temperatures to be 10 degrees colder than those of nearby non-bog areas. There may be as much as a 20 degree difference in some locations. Sprinkler irrigation systems (and flooding on rare occasions) are used to protect the cranberry plants and fruit from freezing temperatures. Sprinklers are the most common method of cranberry frost protection. As the water applied to the plant cools, heat is released preventing the plant from freezing. If a film of water is maintained by continuous application of water, the temperature of the plant tissue will remain above freezing, even if a layer of ice forms. The critical temperature or frost tolerance varies with plant development and color of the fruit. Protection is required to keep the plants above the critical temperature and avoid injury. Preventing frost injury to the flower buds in the spring and to the fruit in the fall is arguably the single most important cultural practice in cranberry production. Frost injury is the only hazard in cranberry production where major crop loss can occur in as little as one hour and total crop loss in one night