The old rule-of-thumb states that cranberry vines need approximately an inch of water a week to grow. Growers use water to protect cranberries from frost and hot weather in summer. As a general rule, each acre of cranberries will use seven to ten feet of water to meet all production, harvesting and flooding needs. There are two main ways cranberry growers bring water onto the bogs – through sprinkler systems and through flooding.
Sprinkler irrigation supplements soil moisture, protects the buds from spring frosts and the berries from fall frosts and cools the plants during intense summer heat. There are two vital operations performed by sprinklers on cranberry bogs - Irrigation and Frost Protection.
Cranberries can require 0.20-0.25 inches of water per acre per day during the hottest, driest and windiest weather. The standard recommendation is for vines to receive an inch of water per week from either rain, capillary action from groundwater, irrigation or some combination of these. Best Management Practices recommend irrigating in the early morning, so as not to extend the time the plants are naturally wet. This practice also minimizes loss from evaporation, run-off and drift, which can amount to 30 percent of water that comes out of the nozzle.
Frost protection applies water to prevent damage to buds and berries when they are sensitive to temperatures below freezing. There are two times of the year when cranberry growers worry about frost – in the spring and in the fall. It is necessary to apply at least 0.10 inch of water per acre per hour to provide basic frost protection. This will protect the plants to about 24 degrees F under calm conditions.
The other practice when cranberry growers use water on the bog is flooding. Flooding is so important in cranberry cultivation that bogs where flooding is not possible are no longer considered profitable. Cranberry growers use flooding as a management tool to protect the plants from the cold, drying winds of winter, to harvest and remove fallen leaves and to control pests.
Cranberry vines may be injured or killed by severe winter weather. This injury, winterkill, is prevented by protecting the vines with a winter flood. The winter flood may be applied as early as December 1 and remains on the bog as long as winterkill conditions are present or forecasted. Generally, growers hold the flood no later than March 15.
Another flooding technique cranberry growers use is known as late water. Late water floods have been used since the 1940’s and have been used to protect the bog from spring frost and to provide some pest control. In modern cranberry production, holding late water refers to the practice of withdrawing the winter flood in March then re-flooding the bog in later April for one month.
The most widely-known use of flooding in cranberry cultivation is for harvest. Approximately 90 percent of the crop is harvested this way. Flood harvesting occurs after the berries are well colored and the flood waters have lost their summer heat. The bogs are flooded with up to one foot of water. In order to conserve water, harvest is managed so water is reused to harvest as many sections of bog as possible before the water is released from the system. Flood water is recycled in the cranberry bog system, passed from bog to bog through canals and flume holding ponds and reused, often shared by several growers.
For a summary of water use in cranberries, view our Water Use Fact Sheet.