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Published: Tuesday, 10 December 2024 at 09:53 AM

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Along with mince pies and crackers containing terrible jokes, cranberry sauce is – in my opinion – one of the great joys of Christmas. And yet for most of us, I suspect cranberries themselves are a bit of a mystery. What are cranberries, and where do they come from?

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UK native cranberries

Our native cranberry (Vaccinium oxycoccos) is a slender, trailing dwarf shrub found in upland bogs, usually creeping about amongst Sphagnum moss. It’s common in north Wales, the Lake District and Scotland, but is very easily overlooked unless you’re actively looking for it. Cranberry flowers are rather lovely, with swept-back petals a bit like a miniature cyclamen, although you do need to lie down in the bog to get a close look at them. For such a small plant, cranberry fruit are surprisingly large, and certainly edible, but are never very abundant, so you would have to work hard to pick enough to eat. For dedicated foragers only I think, and I suspect cranberry sauce would never have been invented if we’d had to rely on our native cranberry.

American cranberries

The cranberries that turn up in your local supermarket, fresh, dried or frozen, and the much larger quantities that are turned into juice or sauce, are American. American cranberries (V. macrocarpon) aren’t all that different from British ones, but both the plants and the berries are bigger. They also grow in exactly the same places: wet, acid, peaty bogs. Originally they would have been harvested from natural bogs, and a few still are, but the overwhelming majority now come from man-made bogs, created by flooding layers of gravel, peat and sand.

Not only are edible bog plants few and far between, cranberry harvesting is unique too. Some cranberries are ‘dry harvested’, using a machine that looks a bit like a lawnmower, but is actually a kind of motorised rake. But most cranberries are ‘wet harvested’, which involves first flooding the whole bog under several feet of water. A machine like an aquatic combine harvester then knocks the cranberries off the vines, which float to the top of the water. The farmers then corral them together with an assortment of brushes and booms, before they’re sucked up into trucks.

Confusing cranberries

Some cranberries are grown in New Jersey, Washington and Oregon, but over three-quarters come from Wisconsin and Massachusetts. The rest of America, having neither the soil nor the climate for growing cranberries, has looked around for alternatives, and the plant they’ve come up with is Viburnum opulus var. americanum. So, despite not being even distantly related to cranberries, this shrub has come to be called highbush cranberry or American cranberrybush. Which, as you can imagine, causes much confusion; indeed if you Google ‘American cranberry’, the first page of hits are almost all about highbush cranberry rather than true cranberry.

Highbush cranberries were eaten by Native Americans, and are still widely used for the same purposes as true cranberries, although as far as I know, only on a domestic scale; there is no commercial industry based on them.

You will by now have noticed that highbush cranberry is clearly a minor variant of our very own V. opulus, or guelder rose, which is therefore a very confusing plant indeed. We call it a rose while the Americans call it a cranberry, but it is unrelated to either. And just to add to the confusion, Americans call our plant ‘European cranberry bush’.

Eating guelder rose?

Bearing in mind that guelder rose is widely grown in British gardens, you might reasonably ask if we could copy the Americans and make our own ‘cranberry sauce’ from its berries. Sadly, I don’t think so. Not only are the two plants not quite the same, but cultivars of highbush cranberry have been bred with superior fruit, something that no-one ever seems to have thought worth doing with guelder rose. As the Missouri Botanical Garden puts it, guelder rose fruits are ‘technically edible, but are very bitter’, and definitely not worth eating.

Of course, if you really want to make your own fake cranberry sauce, you could always grow the American variety; the RHS lists a few suppliers. On the other hand, maybe not – the RHS says ‘Fruit are ornamental – not to be eaten. Wear gloves and other protective equipment when handling.’ They go on to refer you to the Horticultural Trades Association guide to potentially harmful plants, which does indeed contain that warning for the entire Viburnum genus. But the HTA guide also says the same about apple, pear, quince, strawberry and, indeed, cranberry itself, so I’m not sure what to make of that.

For the last word on the subject, I consulted my old copy of Poisonous Plants in Britain, published by the MAFF in the days when there was such a thing. With impeccable common sense, it says that Viburnum berries are ‘popularly considered to be poisonous’, but that they ‘must be considered harmless or of very low toxicity as no definite reports of their causing poisoning have been found’.

So whether you eat Viburnum berries is up to you, but it’s good to know they haven’t killed anyone yet.

Here’s more on poisonous plants

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