Or more importantly, what are sword beans and aerial potatoes?

For aerial potato, think of an alternative to potato. For sword bean, think haricot bean alternative. Both are vines for warm climate food gardens. Fancy something different for dinner?

Aerial potato is a species of yam (Dioscorea bulbifera). It’s a tropical perennial that’s easily grown in a frost-free climate, producing edible tubers along its stems during late summer to winter. Just like passionfruit, Aerial potato can become weedy in tropical and subtropical gardens, so it’s important that if you decide to grow it you prevent it from growing over your fence or up trees adjoining neighbouring properties. Unharvested, aerial potato stems die during winter, dropping their tubers which then sprout the following spring. Vines can reach 5-10m each season, depending upon care.

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I grow mine in a sunny spot in compost rich, freely draining soil. I train it on discarded fishing net attached to a sturdy bamboo wigwam. Originally I grew them over a bamboo archway. The key things are: 1 to provide a sturdy support, 2 to harvest what you grow and – most importantly – 3 site your plant well within your property boundary.

Aerial potato is sometimes available from community gardens and offered at city farms, like Northey Street City Farm in Brisbane. Use aerial potato like ordinary potato. Enjoy the sweet fragrance of their summer flowers and their lush growth. Feed them with compost and poultry manure from summer to autumn so you get a good yield. Store their tubers somewhere dry and well ventilated. If you find mealybug on the tubers during storage, dab these pests with methylated spirits. But above all, keep these vines tamed, trained and harvested, OK?

Sword bean (Canavalia gladiata) is another short-lived tropical perennial vine. It’s sometimes described as being an under-exploited food crop. Provide similar conditions, care and support as for aerial potato. Sword beans can grow 4-7m high in one season, but they are not invasive. They can be cut back hard in autumn, but plants often die in winter. The truth is they’re not reliably perennial, even in the frost free subtropics, and since they crop best in their first year I recommend growing them as an annual, sowing them in mid-spring.

In my garden sword bean flowers are pollinated by blue-banded bees. Large pods, 30-45cm long, are produced towards the end of summer and the seed gradually swell for several weeks (they fatten much more slowly than peas). It requires practice to identify when they’re fully matured, otherwise you don’t get much food out of a pod.

Fresh sword beans can be cooked and eaten. Seed must be peeled and then boiled, so adding them to stews is a good option. Peeling removes their outer skin which contains toxins. These toxins aren’t potent, but can cause nausea if you over indulge yourself. Dried seed cannot be peeled and so cannot be detoxified. Save them for sowing next year.

Neither crops (currently) have any serious pest or disease problems in Australia, but grasshoppers tend to nibble their leaves and leaf-cutter bees (which may also pollinate sword bean flowers) sometimes use pieces of sword bean leaves for making egg laying tubes.

Jerry Coleby-Williams

10th August 2012