Monday, 21 September 2015

Mashua (Tropaeolum tuberosum)

Mashua (Tropaeolum tuberosum) is an herbaceous perennial climber from the Tropaeolaceae family. There are many common names for this plant including maswa, anu, isanu, ysano, cubio, puel or perennial nasturtium. Mashua is very similar in appearance to the nasturtium (T. majus). It is a pre-Incan crop from the cool temperate Andes, the long mountain range to the west of South America, and was thought to be domesticated around 5500 BC.

Mashau (T. tuberosum) grown in a polytunnel in Scotland

Growing mashua

Mashua is easy to grow and can flourish in poor soils without pesticides and fertilizers. It is usually grown from tubers which can be planted out in early spring 80-100cm apart. Tubers vary in colour including white, yellow, purple or red and can be mottled or striped.

If growing from seed sow in the spring under cover. Pot on seedlings and keep protected during the first winter until the plants become established. Plant out during the following summer.

Mashua will grow in full sun or partial shade in moist well drained neutral or acid soil (5.3-7.5 pH). Plants will reach up to 4 metres in height and around 1 metre wide. Earthing up or hilling plants just after the foliage emerges and then again when the plant flowers is thought to increase the yield. Weeding is only required in the early stages of growth. Later a dense canopy of leaves is produced which tends to suppress any weeds. Any dead foliage can be cut back during early spring.

Mashua is frost resistant but may require some protection during the winter months or the further north it is grown. The top growth may suffer in severe weather although well mulched roots will probably survive any extremes of temperature or frost. Mashua can tolerate temperatures down to -10°C. While normally grown at a high altitude, cool conditions rather than a high altitude seem to be what the plant requires. Mashua is able to produce tubers outdoors at sea level at 46°S in Christchurch, New Zealand (Martin et al.1996) and at 49°N in Vancouver, Canada (Johns & Towers 1981).

Most require a short day length (11-13.5 hours/day) to form tubers although low temperatures may be more important for tuber formation than the day length. Research in Finland shows that mashua is unable to produce tubers during a 14–20 hour day length (Kalliola et al. 1990). A popular named variety sold in the UK is T. tuberosum 'Ken Aslet' which produces larger tubers and is not sensitive to day length.

Mashua can be grown as a companion to potatoes, beans, grain, maize, oca and ulluco. Plants have a high resistance to bacterial, fungal, nematode and insect pests possibly because of the high levels of isothiocyanates and other volatile compounds. While a wide number of viruses affect the garden nasturtium, viruses have not been found to affect mashua cultivation significantly (G. Alfredo et al, 2003). Viruses will increase if the plant is grown in the same place year after year.

Propagate by dividing the tubers and replanting in early spring. Alternatively cuttings of basal stems may be taken during the spring.

Other uses

Mashua can be used as an ornamental in a similar fashion to garden nasturtiums. It has several medicinal uses including to reduce sexual appetite and to treat kidney complaints.

Raw edible parts

The leaves, flowers and tubers are all edible raw. Mashua has a pungent hot peppery flavour very similar to nasturtiums or radish. Some plants have a stronger flavour than others. The tubers are probably too pungent and strong to use raw in any great quantity and many consider them an acquired taste. It is common to expose tubers to direct sunlight for a few days to improve sweetness and flavour. Use the leaves, flowers and thinly sliced tubers in salads. The seeds can be used as a cumin substitute. The young seeds and flowers can be pickled and used like capers.

Traditionally the tuber wasn't eaten raw and was cooked before eating in a similar way to any other root vegetable. Cooking removes the pungent peppery flavour.