Cranberry Fruit Image by Alexey Hulsova

If you take cranberries and stew them like apple sauce, it tastes much more like prunes than rhubarb does.

- Groucho Marx

I think in just about every article I’ve written in this series so far, the ‘site selection and planting’ section has begun something along the lines of “choose a well-drained spot in a sunny position”. This month, I’m heading in a different direction and have finally found a fruit crop those of you on boggy ground can take solace in – the true (North American) cranberry. Apart from sweetened, imported cranberry products like cranberry juice and craisins, many New Zealanders have little knowledge of fresh cranberries, and are perplexed by the lovely red, sweet-looking fruit, which they then find to be very sour and sometimes even on the bitter side - they should probably really be considered a ‘savoury’ fruit, hence their affinity with Thanksgiving turkey in the United States. 

So, unless you’re a turkey gobbler, why grow this oddball fruit? Well, with a late autumn harvest period, they fill a gap in the fruiting calendar when all the other berries are long gone. Cranberries contain good levels of vitamin C, and helpful compounds called anthocyanidin flavonoids. They also have high levels of a natural preservative, benzoic acid, and this, combined with the handy anthocyanidins, is what gives cranberries clout in assisting in the prevention and relief of urinary tract infections. If your garden is a bit soggy or if you’re in an area (or have a spot in your garden) with acidic soils, cranberries are great as a long-lived, low-maintenance, cold-hardy groundcover with lovely autumn colour. 

Cranberries: a short family history

True cranberries are not to be confused with the so-called ‘New Zealand cranberry’ or Chilean guava (Myrtus ugni) which belongs to a completely different family, has an upright growth habit and dissimilar-tasting fruit. True cranberries belong to the genus Vaccinium, as do blueberries, and the lesser known (in these parts) bilberries, lingonberries and huckleberries. The plants belonging to this genus are well-known for being dwellers of acidic, boggy locations, thriving in areas otherwise considered wastelands. The two main species cultivated worldwide are the small-fruited Vaccinium oxycoccos, native to Britain and cultivated in central and northern Europe, and the larger-fruited Vaccinium macrocarpon, cultivated throughout the northern United States, Canada and Chile. Harvested for centuries by first nation peoples in North America, English colonists were no doubt delighted to find a larger-fruited variant of their native fruit available when they arrived in Plymouth and Cape Cod. While most of us are familiar with the bush-like growth habits of blueberries, cranberries have a prostrate growth habit and are essentially slow-growing, trailing vines reaching about 20 cm in height. 

Cranberries have four air pockets inside each fruit, and a very tough skin. These unique qualities allow them to float (enabling them to float to the surface during flood harvest operations) and also to bounce (giving rise to the common name ‘bounceberry’, which is also useful in the commercial grading process. The tough skin means they store well fresh after harvest (easily holding for up to six weeks) and their high benzoic acid content acts as a natural preservative. Traditional storage methods included keeping the fresh fruit in barrels of ice-cold water all winter.

What of the name? The cranberry’s delicate pink flowers are borne on long, rigid peduncles or flower stalks, said to look like the head of a crane (the bird, not the machinery), giving rise to its original name, ‘craneberry’. As a result of mispronunciation and/or misspelling, that is now cranberry. Coincidentally, cranes (the birds) are just as at home in bogs as cranberries are.

Suitable climates and growing conditions

Cranberries are very hardy and able to withstand extreme cold, floods (they can tolerate 24 hours underwater without showing any sign of stress), and some wind. Their native geographic zones give an indication of their high winter chilling requirements for fruit set – in the region of 800-1000 hours. The plants take a while to get growing in the spring, but even the tender spring growth can tolerate temperatures well below freezing, -20 to -40°C. Conversely, they can tolerate fairly high temperatures in summer, too.

Cranberries are essentially low-growing perennial vines which produce many long, trailing stems. There will also be some upright growth, which sprout from buds on these runners in the second year of growth onwards. The leaves are small, oval-shaped and initially a dark glossy green during the growing season (spring and summer), moving through shades of crimson-red, purple and brown in autumn and winter with the changing season, then back to their greenish hue the following October. 

The life cycle of a cranberry is somewhat long and drawn out. Plant growth is steady throughout the warmer months and slows in autumn, with the plants going into a hibernation period in the winter months. In New Zealand, the plants flower from the end of November through December, and it is then a further 16 months before they bear fruit. So, flowers from the December 2024 flowering period will not produce fruit until May 2026 and when this harvest takes place, the December 2025 fruitlets will still be green and tiny. A crop for the eternally patient, it seems – but don’t be discouraged if you’re a die-hard cranberry fan! Cranberry plants are generally self-fertile, but like most crops, fruit quality and production benefits from neighbouring plants and the resultant cross-pollination. The flowers are insect-pollinated.

When planting, allow 60 cm to a metre between plants. It takes approximately five years for plants to reach their full fruiting potential in the New Zealand climate. As well as being hardy, the plants are exceptionally long lived: apparently, they can crop for well in excess of 60 years. In terms of yield, you can expect about 0.5 – 1.5 kg of fruit from a mature plant. 

In the USA, where cranberries are grown on a much larger scale than New Zealand, most fruit is harvested by flooding the cranberry bogs with water prior to harvest, beating the berries loose from the vines with water reels in an eggbeater fashion and herding the floating masses of fruit to a collection point.

Cranberries don’t naturally detach from the plants when ripe and you may find it most time-efficient to make a one-hit hand harvest in April-May. For the home producer, there are some nifty berry ‘hand combs’ available (try AliExpress) that consist of a comb-like structure with a pan/scoop attached which you can rake the fruit off the stems with for efficient hand-harvesting.

Cranberries are easy to propagate from their runners – wherever the stems hit the ground, they take root. You can give your older plants a haircut, then simply push the cut sections into pots or beds containing a propagation sand mixture.

Site selection and planting

Plant cranberries in autumn in climates with mild winters, or in spring, after the danger of frosts have passed in colder regions. Choose a spot in full sun or partial shade that is sheltered from strong winds. Cranberries are one of the few fruit crops which require, and thrive, in acidic soils – pH 4 being ideal and the range of tolerance around pH 3 – 5.5. The plants will quickly show signs of chlorosis (leaf yellowing) if the soil is too alkaline.

Where cranberries are grown commercially on the South Island’s West Coast, the local soil type is pakihi – impervious, infertile heath soils akin to swamp. The common local practice is to use a digger to ‘flip’ the soil to produce serviceable land for grazing and cropping. This involves digging down until gravel is hit, then turning the soil over, bringing the lower layer to the surface. For cranberries, a layer of river sand is spread over the top of the flipped land, mimicking methods used in the USA (and their natural growing conditions). The young cranberry plants are planted directly into this. Cranberries have a fine, fibrous shallow root system which doesn’t respond well to disturbance, so plant directly from the containers they have been propagated in into their permanent position and take care when weeding or cultivating mechanically around the plants.

Culture and care

Cranberry plants are generally slow-growing and can easily be overpowered by faster-growing weeds, so make sure to keep on top of these. For small plots, hand weeding should be all that is necessary.

In terms of fertiliser, sulphur-based fertilisers can be applied to keep the soil pH down, and a balanced general NPK blend can be applied sparingly and infrequently, as too much fertiliser applied year-round results in excessive vegetative growth and reduced fruit production.

Although tolerant of wet soils and boggy conditions, timing is everything for cranberry plants. Too much water in the active growing season (spring to autumn) can still be detrimental as this is when root growth is the most active. That’s why commercial growers will often grow in free-draining sand, irrigating when necessary. 

Pruning

Cranberries fruit on the previous year’s growth, so a light prune to remove stems that have gone straggly or become intertwined is all that’s necessary. Trimming the tips of stems back can encourage the plant to bush out and produce more fruiting laterals. 

Pests, diseases and what to do about them

Cranberries are highly tolerant of pests and diseases – hurrah.

Varieties: My top picks

Bergman – early cropper, ripe around March. Medium-sized fruit with good flavour. Lower chilling requirements than Crowley. Strong autumn colour.

Pilgrim – good cropper with large fruit, ripe mid-April, performs well under New Zealand conditions.

Stevens – ripens late April.

Crowley – Commercial US variety, particularly suited to groundcover use.

 What to do with your crop

Move over packets and jars of over sweetened commercial cranberry products – fresh cranberries aren’t that difficult to prepare. They will keep in the fridge for at least six weeks and can be frozen quite satisfactorily for a year or more. 

Culinary doyenne Jane Grigson recommends caution in their preparation – if you add sugar to cranberries at the start of cooking, the skins will toughen, so keep sweet additions for once the fruit is cooked and already tender. For simple sauces and such, she recommends no more than half the fruit’s weight in sugar, as adding an excess exacerbates bitterness.

Being a sucker for lemon (or any fruit) curd, I’ll soon be trying out my standard citrus curd recipe that you can find here and substituting the lemon juice and rind for 340 g fresh cranberries, cooked down with a little water to a smooth puree. 

Cranberries pair well with oranges and pears and their tartness can be balanced in sweet baking by creamy tart fillings, crisp meringue or spiced crumble-like toppings. If you’re a fan of the traditional English summer pudding (I am not), try a winter version using frozen raspberries and fresh cranberries. Or substitute dried, sweetened cranberries for chopped fresh cranberries in your go-to fruit loaf or cake recipe. 

Keeping with the Thanksgiving vibe, pair cranberries with squash or pumpkin in your favourite recipes for a great flavour (and colour) contrast.      

If you’re a cranberry fan but have no interest in growing them, frozen New Zealand-grown cranberries and a range of fantastic ready-made compotes and sauces are available online here.

Disclaimer: the information supplied above is of a general nature and provided as reference material only. In regards to pest and disease control, please consult your agrichemical consultant for suitable products, application rates and further region-specific information.

Anna-Marie Barnes is an active member of the New Zealand Tree Crops Association who endeavours to grow and preserve as much of her own fresh produce as possible.  When the weather’s no good for gardening, she can usually be found inside working on a batch of homemade cheese or soap.     

The New Zealand Tree Crops Association is a voluntary organisation promoting interest in useful trees, such as those producing fruit, nuts, timber, fuel, wood, stock fodder, bee forage and other productive crops.  Find out more about the NZTCA here: https://treecrops.org.nz/

Image credits

Cranberrys – Image by Inga via pixabay.com
Cranberry fruit - Image by Alexey Hulsova via pixabay.com
Cranberry bog- Image by Neeme Katt via Pixabay.com
Cranberry harvest - Image by PublicDomainImages via Pixabay.com