Return of the lost crops of the Incas

In the same way that I have a soft spot for eccentrics and oddballs of the human kind, so I've always been intrigued by the horticulturally strange and the botanically forgotten. Take, for example, the lost crops of the Incas, the South American people whose civilisation was famed for its sophisticated agriculture and the diversity of food crops that it cultivated, including many different grains, tubers, legumes, nuts, fruit and vegetables. At its peak, this vast, climatically diverse empire measured more than 4,000km, stretching from southern Colombia to central Chile before it finally fell to the Spanish conquistadors in the mid-16th century. Yet, despite its size, it was also highly organised and capable of producing food for more than 15 million people.

I say “lost crops”, but not any more. Many of these plants – including mashua, oca, maca, yacon, Inca berry, pepino, quinoa, achocha, amaranth and kaniwa (Chenopodium) – are being cultivated both outdoors and under cover by a new generation of Irish gardeners who prize them for being nutritious, tasty and versatile, as well as productive and easy to grow. In doing so, they’re continuing a tradition of growing Inca food crops that began with the introduction of now commonplace kitchen garden plants such as potatoes, tomatoes and peppers.

Take achocha, an easy-to-grow member of the cucumber family with fleshy, edible, decorative fruits that can be eaten raw or cooked. Consumption of its tender fruits is also believed to help reduce cholesterol. A tender annual easily raised from seed sown in April-May, this fast-growing plant will romp through a polytunnel and so is best planted outdoors in June in a sunny protected spot in the garden/allotment, where its winding stems require some form of support. Many varieties are available, including the high-yielding Giant Bolivian (realseeds.co.uk), whose especially large fruits are ideally suited for stuffing and roasting,

Another Inca crop gaining popularity with gardeners is quinoa, a high-protein seed crop that Madeline McKeever of Cork-based Brown Envelope Seeds says “is happy even in the most miserable Irish summer”.

She advises direct-sowing it in April-May for harvesting in September. Brown Envelope Seeds (brownenvelopeseeds.com) also supplies the seed of many other traditional Inca food crops: these include colourful, decorative varieties of amaranth (used for its grain), maca (a root vegetable famed for its hormone-regulating properties) and different squashes, as well as Chenopodium, whose succulent leaves can be used in salads, and its edible flowers dipped in batter and fried.

Two other Inca crops also worth experimenting with are the pepino (Solanum muricatum), whose sweet, juicy fruits are prized for their tastiness (available as seed from Thompson &Morgan) and the golden Inca berry or Physalis peruviana (seed available from Westport-based Seedaholic. com). Sow now, under cover, to grow in a polytunnel/glasshouse/sunny conservatory.

Potatoes aside, the Incas grew many other tasty, productive, nutritious tuberous crops that are suitable for cultivation under cover in Ireland. Among them is yacon, "the underground pear of Peru", whose sweet, juicy tubers boost the digestive system. Closely related to the dahlia, yacon can be planted as rhizomes into pots at this time of the year, then grown with heat and under cover, for transplanting into the polytunnel/greenhouse in mid-late May.

Be warned that along with requiring a fertile, free draining soil enriched with manure, the plant quickly reaches giant proportions, with an average height and spread of 2m x 1m. Its tasty tubers should be harvested after the first frost and can be eaten raw, in a fruit or savoury salad, or lightly steamed or roasted. They also store well.

So does oca, a favourite food crop of the Incas and still wildly cultivated in the Andes. Its colourful tubers can be planted into the polytunnel/glasshouse in April/May, or as young plants from late May. Much lower growing than yacon, this hugely productive plant likes a fertile, neutral to slightly acid soil, full sun/light shade and plenty of water. Harvest the tubers in late autumn/ early winter, leaving them to dry out for a few weeks to reduce acidity, before eating raw or boiled/roasted as an addition to stews and soups.

Finally, don’t forget the sweet potato, yet another highly nutritious and versatile tuberous Inca crop that enjoys fertile soil, lots of moisture and warm temperatures and grows well in an Irish polytunnel. Plant it under cover as rooted cuttings/young plants in late May/early June.

As to the once thorny question of where Irish gardeners can source propagating stock of these tuberous vegetables, there’s some great news.

Excited by their potential as food crops, some years ago Pat Fitzgerald of Fitzgerald Nurseries in Kilkenny began a selection programme to single out the tastiest and most productive varieties – the first programme of its kind in Europe. His nursery now produces an award-winning range of young oca, yacon and sweet potato plants (mashua and ulluco plants will follow next year). These will be available in Johnstown Garden Centre (johnstowngardencentre.ie) and Lidl stores for a limited time next month (from May 28th), allowing Irish gardeners to discover a little of the lost treasure of the Andes.

This week in the garden . . .

Seed of early peas (suitable varieties include "Hurst Green Shaft", "Kelvedon Wonder", "Feltham First" and "Avola", or "Half Pint"/"Tom Thumb" if growing in containers) can be sown direct into the ground this month. Sow generously into well-prepared soil either as single or double rows. After sowing, cover the ground with netting/ chicken wire to prevent rodents and birds from stealing the seed and erect some form of sturdy support that will take the weight of the plants when laden down with pods.

If you didn't remember to cut back lavender bushes late last summer, then you can lightly cut them back now – just make sure not to cut back into the old wood. Do the same for the silver-leaved shrubs Santolina (cotton lavender) and Helichrysum (curry plant).

As light levels intensify and daytime temperatures continue to rise, it's important to keep glasshouses/ polytunnels well-ventilated to prevent damage to seedlings and young plants. But as temperatures can fall again swiftly with nightfall, make sure to close doors and ventilation panels again in the evening. When night-time frosts threaten, protect young plants with layers of horticultural fleece.