How to grow mashua

You can boil, mash, roast or fry this Andean tuber. Even the leaves taste good

In this damp, cool weather, most of the garden is tumbling into decline, yet one plant flourishes. Mashua has spent the autumn sending out tendrils, racing upwards and triumphantly flowering where it finds the most sun; below ground, its tubers are fattening up.

Mashua, Tropaeolum tuberosum, is a perennial cousin of the nasturtium. It comes from the cool, tropical highlands of the Andes, where it is grown as a food crop. It’s a tough cookie: in the right conditions its vines can grow three metres high or more, it thrives on neglect, is unbothered by pests and can happily produce up to eight kilos of tubers per plant a season. What’s not to like?

Well, there’s a hitch or two. First, as with many plants from the high Andes, it likes long days and short nights. Tubers start to form only after 12 or more hours of sunlight a day and take time to mature. This means that if we have a hard frost in the next few weeks, it will put an end to the delightful foliage and the tubers will stop fattening.

On top of that you have to actually like the tubers. They resemble Jabba the Hutt, a sort of voluptuous slug shape in a variety of yellow, white or white flecked with red. Their taste divides the world – either you think they are rank, or you think they are pleasingly sweet with notes of aniseed and pepper. If you freeze them after cooking and then reheat them, you can increase the sugars so they taste more like sweet potatoes.

If the tubers split opinions, I can’t imagine that many won’t like the attractive deep blue-green leaves with a scalloped edge. They taste deeply green – grassy, sweet and with a gentle hit of pepper. They work incredibly well in sandwiches, elevating a roast chicken or cheese sarnie with their frilly edges poking out like a petticoat.

As nothing seems to eat them in great numbers, you can pick the leaves from late spring to the first hard frost with little tending on your part. In fact, the whole plant is packed with insecticidal and bactericidal compounds, which is why it is traditionally interplanted between other Andean crops, such as potatoes and ocas, to ward off insects.

There is one cultivated form to seek out: Ken Aslet, bred to be day-length neutral and thus flower earlier, usually in August. You can grow mashua in any manner of spots: poor soils; pH anywhere from 5.3-7.5; in sun or part shade.

It makes an excellent container plant: I grow mine in a 50-litre pot along my north-west facing fence, which gets a good blast of sun late in the day. And I still get enough tubers to mash, fry (by far the best cooking method), grate, boil and roast.

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