Even potatoes get the blues

Our blue potatoes always surprise visitors to the Secret Garden Club. Historically potatoes have been cultivated in all shapes, sizes, and colours, and even today in the potato's original home in the Peruvian Andes you'll find many varieties available that would be completely unrecognisable to us. Potatoes in red, white and blue, very small, very large, irregular in shape, or long and thin. A far cry from the choice of big bakers vs small new potatoes that we tend to get in supermarkets here.

Salad blue potatoes: the pigment is an anthocyanin, an antioxidant also found in blueberries, blackberries, blackcurrants, cherries, grapes and red cabbage.

But blue potatoes, with skins of deep purplish-blue and purple flesh which cooks to a deep indigo, even Wedgwood blue, are still treated as a novelty in the UK, despite the fact that they have a long history in South America. We're often asked if the colour has been injected into the tuber - the answer is, of course, no. The blue pigment is caused by the presence of an anthocyanin, which is an antioxidant, leading nutritionists and others to attribute greater health benefits to blue potatoes. 

The specific variety we grow at the Secret Garden Club is Salad Blue, which is something of a misnomer as it's not actually a great for using in potato salad. It doesn't hold its shape too well when boiled, and does much better when steamed, chipped, roasted, sauteed or baked. It also makes spectacular blue mash (cook by steaming or baking before mashing).

Salad Blue potatoes as a distinct variety were first cultivated in Scotland in the 1900s, so they are well adapted to our climate. They are no more difficult to grow than any other potato, liking a slightly acid soil, and disliking frost.

We planted tubers in the open ground in late April, a bit later than usual as spring was so cold this year, and covered them with good compost. As the plants grew, we earthed up the stems (or 'haulms') drawing up soil around the plant, This ensures that all light is excluded from the growing tubers underneath - potatoes exposed to the light will turn green and poisonous. We also save grass cuttings from mowing the lawn and heap them over our potato plants: it's a little more unsightly than neatly earthed-up rows but it does the job.

We dug the potatoes up at the Secret Garden Club's Food From The Americas afternoon at the beginning of September, again, slightly later than usual thanks to the late growing season. These can be stored in a dark, cool place, in a paper bag or sack - don't keep them in plastic or they'll go soggy and don't keep them in the fridge, around 14-16 degrees is best. In practice, though, they are more often eaten up quickly.

While the blue varieties are just as versatile in the kitchen as 'ordinary' potatoes, it makes sense to cook them to show off the unusual colouring. Last year, for the Jubilee, the Secret Garden Club's Kerstin Rodgers created whole dressed salmon with Union Jack mash from red, white and Salad Blue potatoes for a feature in The Independent. We've served red, white and blue chips at the Secret Garden (always particularly popular with children) and earlier this year at our Heritage Potato afternoon, we served baked blue potatoes with creme fraiche and caviar.

For our American food afternoon, one of the dishes served was squash, blue potatoes and aubergines in a savoury chocolate sauce, or mole, (see photo, top). The aubergine is a bit of an interloper here. While the other ingredients are all American in origin, aubergines, despite being related to potatoes and tomatoes as members of the Solanum family, are actually native to Asia. We also used an Italian squash cultivar, Berrettina Piacentina, which has rich, dense and relatively non-fibrous flesh, so holds together well in a casserole or stir-fry.

You can find blue potatoes occasionally from farmers' markets and on mail order from Carroll's Heritage Potatoes. Seed potatoes for planting also available from Carroll's in early spring.