Because cranberries are a perennial crop, they must survive Wisconsin's harsh winters. Even though the vines go dormant, they must be protected against widely fluctuating temperatures and drying winds. As the fruit begins to color in late August, the plant has already begun its preparation for winter dormancy. By December, the dormant vines are flooded with water that quickly freezes into a solid covering of ice. The ice protects the cranberries from extreme cold and fluctuating temperatures as well as preventing the winter winds from drying out the vines.
Cranberry vines grow longer each year.
Placing a thin layer of sand over the vines every few years helps rejuvenate the planting by keeping the fruiting buds closer to the root area of the plant and helps control weed, insect and disease pests. It is easy to sand in the winter when the vines are covered with ice. Dump trucks are driven onto the ice over the beds and about one-half to one inch layer of sand is spread uniformly on the ice with a sander. As the ice melts in the spring, the sand settles onto the surface of the beds. New plantings may be sanded each year for two or three years to stimulate rooting and aid runner and upright development.