Crop breeding

Fun facts about cranberries for Thanksgiving!

Cranberries are an essential part of many a Thanksgiving meal in the U.S. and Canada. The annual family debate is about the best way to eat the beautiful, red fruit. Whether you prefer whole-berry sauce, jellied sauce, or relish, these fun facts may raise your Thanksgiving cranberry conversation to the next level!

red berries of cranberries on green bushes

Wild cranberries growing on the coast of eastern United States. Credit: Lela Nargi

Cranberries are a native North American fruit. Wild populations of cranberries can still be found in acidic sphagnum bog habitats throughout the U.S. and Canada. Native Americans living in these areas used fresh and dried cranberries extensively. They were a source for food and medicine. They even made pemmican – a blend of dried meat, fat, and dried berries that served as a great travel food. The unique biology of cranberries affects how we grow and manage the crop, as well as how it is harvested.

Growing Conditions

In the wild, cranberries grow best in the open areas of sphagnum mats that form around the edges of acidic bogs. Cranberries are a wetland plant, not an aquatic plant, and require both abundant water and excellent drainage of the root zone. They are essentially growing in the top layers of a floating sponge, but not in the flooded portions of the mat.

In commercial production, cranberry beds all have a sprinkler irrigation system to supply abundant water during the growing season. The beds are surrounded by a ditch to keep the root zone well drained, and a dike to allow flooding at harvest and over the winter. Cranberries require acidic soil; soil pH between 4.0 and 5.2 is ideal. Without lots of water, good drainage, and low soil pH, cranberries will not grow well.

Can you grow your own cranberries? Most likely! If you want to grow your own cranberries, a raised bed or pot filled with soil heavily amended with peat moss would be a good start; you should also plan for regular watering. If you live in an area with a limestone aquifer and higher-pH water, you may need to apply sulfur amendments to keep soil pH in the correct range.

Crop Management

cranberry bog with red leaves in November.

Wild cranberries (low-growing red plants) growing on a floating sphagnum mat in November, central Wisconsin. Cranberry leaves change color from green to red as they become dormant in the fall. Credit: K Kosola

When considering management of the crop, it helps to picture cranberries as tiny versions of fruit trees. Like many other fruit crops, cranberries are woody perennial plants. Flowers are produced on fruiting uprights that put on around new growth every year; the flower buds are thickest on the newest wood.  The fruiting uprights grow at intervals along a ground-hugging vine. If you apply too much nitrogen, flowering is suppressed, and the plant produces abundant vines. In extreme cases, the plant will stop flowering entirely; it is possible to lose the entire crop from over-fertilization. For home gardens, application of a fertilizer labeled for rhododendrons and azaleas could be used, but with a light touch. In a home garden bed heavily supplemented with peat, you may not need any fertilizer.

A hard frost at any time during flowering and fruit growth and development has the potential to wipe out a crop. As with other fruit crops, cranberry growers use sprinklers to protect the developing crop. The heat of enthalpy released during freezing keeps temperatures above the temperature where damage occurs. You can pick out a cranberry grower’s truck by the spotlight on the driver’s side. Cranberry growers patrol their cranberry beds on frost watch nights to make sure all the sprinklers are working. Growers can’t count on a full night’s sleep during the growing season, because frost forecasts could happen at almost any time. As a gardener, you could use a spun-bond polypropylene row cover to protect the plants rather than staying up all night with a flashlight and a sprinkler!

Establishing a commercial cranberry bed is a substantial economic commitment but when done well, they can be productive for many decades. Cranberry growers have a very long-term perspective when managing their farms. When I was at the University of Wisconsin, I did field research in some cranberry beds that were 80 years old, and still producing fruit. Just like larger fruit trees, it can take up to four years to get substantial fruit production after the initial planting of vine cuttings into a new bed.

Cranberries do best with some renewal pruning once they are fully established, since new woody uprights produce more fruit. The most common pruning practice is sand application. Every few years, growers drive dump trucks onto the ice in the winter to spread the sand over the cranberry beds. When the ice melts, the sand layer buries the lowest layer of existing vines, and promotes growth of roots and new uprights. A soil core taken in an old cranberry bed has a striped pattern of alternating sand and leaf litter plus vines that reflects years of regular sanding.

Fruit Harvest

cranberry bog in spring with water in ditches

Cranberry bed in Warrens, Wisconsin after a heavy spring rain. The bed is graded to ensure water does not pool, and drains to the ditches on the edge. Leaves are starting to green up as the plants come out of dormancy. Credit: K Kosola

Cranberry fruit floats amazingly well – the hollow spaces in the fruit make it highly buoyant, which is a real advantage for a plant that grows at the edges of a floating sphagnum mat. The small, red fruit is highly attractive to birds and mammals (like us!), which eat the fruit and spread the seeds widely. In the most common harvest practice, growers will apply a shallow flood to the bed, and then use self-propelled beaters to knock the fruit loose. The floating fruit is corralled with booms, and then lifted into trucks with a suction system, before being trucked to a processing plant.  Fresh fruit is sometimes cleaned and packaged right on the farm.

Cranberry breeding

Traditional varieties were selections from wild populations of cranberries. Cranberries are an example of a plant that is in the process of domestication. The USDA started a breeding program with a round of hybridizations in 1929. In 1950, they released first-generation hybrid varieties that are in common use now.

Teams at Rutgers and UW-Madison have active cranberry breeding programs. Most cranberry products have some sweetener added, as the fruit is acidic and astringent. One team is working on a sweeter cranberry variety as a potential fresh-fruit treat! Breeders are also working on traditional breeding traits, such as:

  1. increased yield,
  2. improved berry quality,
  3. improved berry nutrition, and
  4. disease and pest resistance.

Cranberry operations are often family farms, with multiple generations involved in running the business.   Because of the requirements for specialized growing conditions and dedicated facilities to manage post-harvest fruit processing, cranberry production is concentrated in a few areas. The top growing states in the U.S. are currently Wisconsin, Massachusetts, and New Jersey.

Uses of cranberries extend beyond Thanksgiving. They are now used as sweetened dried cranberries as a snack or in salads. You might enjoy a fresh drink of cranberry juice or Cosmopolitans. No matter how you enjoy cranberries, think about where this fruit originated, its place in Native American culture, and the farmers that grew the fruit you are eating.  It is a fascinating example of a crop grown on a relatively small number of acres that has broad impact as part of a diverse diet.

Answered by Kevin Kosola, Monsanto

To read another blog about cranberries, visit this blog.

About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.

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