In North America, the cranberry or American cranberry (Vaccinium macrocarpon, formerly Oxycoccus macrocarpus) is traditionally served with turkey at Thanksgiving, Christmas and New Year’s Day meals, either as a jelly or a sauce. Its juice is also popular all year long. In fact, cranberry juice has been rapidly gaining in popularity in Europe and Australia as well, where it is seen as a health food, given that the cranberry is known to be particularly rich in antioxidants.
There are now cranberry farms throughout North America and Northern Europe and even a few in Chile, yet very few gardeners think to try and grow it this plant in their home gardens, largely because of the misconception that the plant is aquatic, not something you could grow in the average vegetable bed. This comes for the fact we regularly see television images of cranberry harvesting where massive quantities of berries can be seen floating in water.
In fact, however, the cranberry is a terrestrial plant. It normally grows in peat bogs, rooted in sphagnum moss, but also in poor, acid, well-drained soils. True enough, it doesn’t like to dry out entirely, but to conclude it actually grows under water is quite a different story.
The misconception that the cranberry is aquatic comes from an interesting fact: when mature, the berries float! And cranberry growers have learned how to take advantage of this detail by carrying out what is called “wet-picking”.
Rather than sending in teams of workers to harvest the very low-growing berries on their knees, growers flood the beds. This is easily to accomplish, as commercial cranberry farms build vast beds surrounded by dikes. When the fruit ripens in the fall, all they have to do is to flood the beds, then run a mechanical harvester over the plants to knock the berries loose. They then float to the surface where they can be pumped into a truck, strained, then sent off to a factory for processing.
In the Home Garden
You won’t have to flood your vegetable bed or run a harvester over it to raise cranberries in a home garden. In fact, they’re not at all difficult to cultivate… in cold climates, at least.
Cranberries are native to the boreal forest (taiga), found growing wild throughout much of eastern Canada as well as in the colder regions of the northeastern United States. They’re very cold hardy (to zone 2) and in fact they won’t bloom without a long, cold winter. That’s why they’re rarely grown in zones 7 and above.
The American cranberry is a creeping plant with small, oval, dark green leaves. They’re evergreen, but do turn reddish in late fall. It produces two sorts of stem: long creeping stems that root where they touch the ground, forming an ever-widening carpet, and upright stems (never more than 1 foot /30 cm high) that produce the majority of flowers and fruits. The cranberry actually makes an excellent ornamental evergreen groundcover!
The pink flowers are small, with backward-curved petals and a long extended style and stamens pointing downward. In fact, its the beaklike style and stamens that gave the plant its name. European settlers thought the flowers looked like tiny cranes (storklike birds) and called the plants crane berries, a name that eventually became cranberries. This type of flower is quite unusual for a plant in the Ericaceae (heather and rhododendron family): most of the others have bell-shaped flowers.
The berries, green at first, redden as nights get colder in the fall, eventually turning a dark purplish red. They often remain on the plant through the winter if they aren’t harvested. They are large compared to the size of the plant and this explains their Latin epithet: macrocarpon means big fruit!
The berries are rarely eaten fresh because of their astringent taste, but cooked with sugar, they are delicious!
How to Grow Cranberries
Plant cranberries a sunny spot. Partial shade is also acceptable, but results in fewer fruits.
The only real challenge growing them is to provide acid soil (a pH of 4 to 5). Typically this means digging a trench about 1 foot/30 cm deep and replacing the soil removed with a 50/50 mixture of peat moss and sand. If the surrounding soil is heavy clay, that could however lead to poor drainage, so it may be better under such conditions to build up a 6-inch (15-cm) mound of sand and peat moss over the existing soil rather than digging a trench.
I repeat, popular belief aside, cranberries are not adapted to soggy soil: normal soil moisture – that is, evenly moist soil – is quite adequate. Reserve your watering for cases of serious drought: cranberries will not tolerate drying out completely. But beware of overwatering under other conditions.
Little fertilizer is required. Too much fertilizer, especially one rich in nitrogen, the first number, tends to stimulate stem growth at the expense of fruit production.
Curiously, the colder the climate, the less this plant needs attention. In zones 2 to 5, just plant it, water it a bit the first year, then let it grow. No special care is needed other than to prune back any stems that wander too far.
In regions with mild winters, though, there is a risk the plants will awaken too early in the spring, then get killed back by a late frost… and that will eliminate the harvest for that year. Growers in mild climates often cover the soil with straw mulch or plasticized agrotextile once it is frozen in order to keep the soil from thawing out too early. Or they may even flood the bed a second time in late fall, as water is slower to warm up than soil. The idea is to keep the ground cold as long as possible, hopefully until all risk of frost has passed.
As for harvesting, wet-picking won’t be necessary when you grow cranberries on a small scale: just harvest them by hand when the berries are fully ripe, usually in October.
When it comes to propagation, the plant pretty much takes care of that on its own, spreading readily though wandering stems that root to form new plants where they touch they ground. To start a new planting elsewhere, therefore, simply dig up sections that are already-rooted and move them. You can also start new plants from stem cuttings. Growing cranberries from seed, however, is slow and complicated, best left to specialists.
There are 3 other species of cranberry, of which only the lingonberry (Vaccinium vitis-idaea), also called cowberry or patridgeberry, with small red berries, is cultivated to any extent. As a circumboreal species, it grows in the boreal and even arctic and alpine regions of Eurasia and North America. It requires much the same growing conditions as its bigger-berried cousin.
Why not try giving growing cranberries a try? It will certainly make you stand out from the average-gardener crowd!