Cranberries (Vaccinium macrocarpon) are a native plant that has had a big increase in consumption in the last 20 years, taking them from a Thanksgiving treat to a year round health food. There are European varieties of cranberries but they have a different taste and somewhat different nutritional profile and are called ligonberries.
Cranberries have compounds in them that inhibit bacterial activity and have long been used to fight urinary tract infections. These same compounds also inhibit the bacteria that cause ulcers and gum disease. Cranberries also have antioxidants which reduce the formation of LDL or “bad” cholesterol and this is thought to have a beneficial effect on the cardio-vascular system. They are also tasty and provide many vitamins, including vitamin C. Raw cranberries have no fat and only 47 calories per cup.
Cranberries are grown commercially in New Jersey, Massachusetts, Oregon, Washington, Wisconsin, Delaware, Maine, Michigan, New York, Rhode Island and many areas of Canada. They are also being grown commercially in Chile. While they are not as easy to grow as other small fruits gardeners in the above states can also grow cranberries if they take some care to provide proper conditions.
Cranberries don’t need to be in water
Cranberries are low trailing vines that produce daughter plants much like strawberries. The plants are evergreen and perennial. Cranberries need moist, peaty, acidic soil, a good winter chill but a fairly long frost free growing period to thrive. They grow well in zones 2-5 and possibly zone 6. Contrary to what most ads and other illustrations suggest cranberries do not need to be submerged in water to grow. In fact the plants will die if submerged for very long. They prefer layers of peat soil and sand that hold some moisture but are not waterlogged.
The reason the cranberries grow in water idea is common is because in some commercial cranberry farms the fields are flooded to harvest the berries. Cranberries have pockets of air in them and they float. Fields are submerged, the vines raked and shook and the berries float on the surface. “Booms” swirl the berries into chutes that drain off the water, leaving the berries behind. About 90% of the commercial cranberry harvest is done this way and the cranberries are used for juice and canning, or making that Thanksgiving treat, cranberry jelly.
The other 10% of the commercial cranberry harvest is picked dry. Workers use hand rakes and small “combing” machines to gather the berries. These berries are used for fresh berries you pick up in the produce department or at farm markets.
Making a cranberry bed
If you want to try and grow cranberries you will probably have to grow them in beds modified from your existing soil. Most people do not have the acidic peat soil needed for good cranberry growth. You will need a sunny area with an abundant supply of water nearby. You can make raised beds or even better, sunken beds. Here’s the general idea.
Dig out existing topsoil from your intended bed down to about 8-12 inches. The deeper range is for heavy clay soils. (Or make raised beds about 12 inches deep.) Beds should be at least 4 feet wide by 8 feet long for a modest harvest. You can move the topsoil somewhere else or mound it along the sides of the excavated area (or around your raised bed frame). This makes a nice sunken area to hold water when you irrigate.
Add 2 inches of coarse sand to the bottom of your bed. Then fill the bed with 6 inches or so of sphagnum peat, (not “Michigan” peat). You can also use a mixture of sphagnum peat and shredded bark. Mix in some slow release acidic fertilizer such as that sold for azaleas or blueberries. About a ½ pound per 4x8 foot bed will work. Add about an inch of coarse sand to the top of the bed.
General care of cranberries
Cranberries can be grown from seed but germination is slow and difficult. It is better to start with plants. Cranberries begin fruiting at 3 years of age so the older the plants the better. Spring planting is best but they can also be fall planted. Space the plants about 18” apart for less than 3 year old plants, 3 feet apart for mature 3 year old plants. The plants will send out runners to fill in the bed. Three year old plants will also start some upright growth and it’s on the upright growth that berries will form.
Keep the bed well watered from planting to harvest. The soil should feel moist at all times but not have water pooled on top. Peat holds a lot of water so don’t add water until you feel the planting medium. It should feel moist down to at least 6 inches. Keep your cranberry bed well weeded as they do not tolerate weed competition well.
After the ground freezes in the fall cranberry plants need heavy mulching. While they are evergreen they tend to dry out and have a lot of winterkill unless covered by deep snow or mulch. Use straw, shredded leaves, shredded bark, or pine needles and bury the plants. Remove the mulch in early spring, usually about the time daffodils are blooming. The plants will be putting out new growth and this is cold sensitive for several weeks. Keep the mulch nearby to reapply or buy some floating row cover,( a spun fabric sold in garden stores). If temperatures are predicted to go to freezing or below cover the plants.
After the first year reduce the fertilizer, adding only a small amount, ¼ pound or a cup or so, to a 4 x 8 bed in the early spring. Add a little fresh sand to the top of the bed each spring also. If beds get too crowded with plants some of them can be removed to form other beds or to give to friends.
Cranberries are not self-fertile and they need insects to pollinate them. Bumblebees are the best pollinator. The flowers appear in early spring and can be damaged by frost. Keep some row cover material or old sheets around to cover the bed should frost threaten.
Home gardeners will pick cranberries by hand in the fall. The berries are ripe when they are deep red and the seeds inside are dark brown. A hard frost will ruin the berries so pick them before it happens. The berries will store in the refrigerator in a sealed container for about 2 months. You can also can them, turn them into jellies and sauces or freeze them.
If you like fresh cranberries and want to have control over how your food is grown try growing some cranberries in the garden. The plants will produce for many, many years so the initial expense and work involved in the beginning will be worth it.
Here are some additional articles you may want to read.
Edible landscaping that also provides fall color
How to grow elderberries
The fascinating history of poinsettias
You can contact the author or sign up for her weekly garden email newsletter by writing her at firstname.lastname@example.org