Yams are warm climate, winter herbaceous, perennial vines. The swollen, starch-rich tuber is their food store, and this is what most people grow them for – they use them as a potato alternative, baked, boiled, mashed or as chips.
Yams need a frost-free, coastal climate and succeed best where there is summer rain and winter drought. They grow well from Sydney north to FN Queensland and around the Top End and south to Perth. While they’ll grow well in coastal WA, they will need plenty of water.
I grow yams because potato is an unreliable crop in Brisbane. I grow two kinds: winged yam, Dioscorea alata, and aerial potato, D. bulbifera. They belong in the Dioscoreaceae family. Yams are highly productive, trouble-free, water efficient and space saving compared to potato (Solanaceae).
In my garden, Winged yam (pictured) can produce a tuber weighing between 15 – 30kg in one growing season. Aerial potato produces tubers in leaf axils on the vine and these are large enough to harvest as well as the tuber in the ground, but they are less productive than winged yam.
Cultivation: To grow them you’ll need compost rich, freely draining soil. I grow my best by planting them in a hole dug two spades deep backfilled with home-made compost. For best returns, water them deeply once a week in dry weather. Give each plant one handful of poultry manure every six weeks during the growing season. I foliar feed mine every fortnight using seaweed.
Winged yam is a vigorous vine, growing to about the spread of a mature passionfruit in one year. In Pacific countries they’re usually planted around the drip line of large trees. Their stems are trained up bamboo canes so they can grow through the canopy unrestricted. Their twining stems readily grow against a fence fitted with wire mesh.
If space is limited, one winged yam can be grown in a space 60cm x 60cm and trained up a sturdy wigwam 3m high. When plants reach the top the cascading growth can be tied in as it descends. They look very attractive trained this way. Just make sure the support is sturdy, as these vines become heavy in summer storms. We filmed harvesting a winged yam grown this way for Gardening Australia.
Aerial potato (Dioscorea bulbifera) reliably produces 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 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.
I enjoy the sweet fragrance of the summer flowers and their lush growth of aerial potato, but I’ve never seen winged yam bloom. But above all, keep aerial potato vines tamed, trained and harvested, OK? Aerial potato is sometimes available from community gardens and offered at city farms, like Northey Street City Farm in Brisbane. I share my surplus during my Open Days.
The key things are:
1. provide a sturdy support
2. harvest what you grow, and
3. site plants well within your property boundary so none escape
Pests: Yams currently do not have any serious pest or disease problems in Australia. Grasshoppers eat their leaves and leaf-cutter bees (which are beneficial pollinators of legumes) sometimes use leaves for making their egg laying tubes. You may find mealybug on stored tubers. Simply dab these sap sucking pests with methylated spirits.
Harvesting: Yams are winter deciduous, an adaptation to coping with the winter dry season. In autumn their leaves fall, and during winter their stems gradually break up into pieces. Our cue to harvest yams is when their leaves start dropping.
Aerial potato tubers are easily picked off. Save the best for eating and use the smallest for planting.
Winged yam tubers must be dug out carefully because they are fragile. They can grow 50cm or so deep and digging may split them into pieces. After gently cleaning the soil off them, you’ll notice the crown will contain one or more tuberlings (see images).
Winged yams that are starved of water tend also to produce axillary tuberlings. Unlike aerial potatoes, which have smooth skins, the tuberlings of winged yam are covered with grooves. Tuberlings are a survival mechanism, and well watered winged yams don’t produce many: five plants here covered a 30 m long fence and only produced four axillary tuberlings. These are worth gathering for distribution because there are few sources of winged yam.
Harvest time can also be planting time. Yams planted in the cool season won’t need any water until they begin sprouting. In my Brisbane garden this is around October.
Storage: I carefully clean tubers of soil and store them under the house. I have never had to protect them from damage by rats. When I want to cook some winged yam, I just slice off what I need. The cut end will dry, seal and heal without going mouldy – as long as they are stored in a cool, dark, dry, well ventilated space.
Tubers stay fresh until growth resumes in spring. When growth resumes, tubers rapidly become spongy and unpalatable because growth removes moisture and nourishment.
Hunting for planting material: There are hundreds of yam cultivars around the tropical and subtropical regions of the world. The Seed Saver’s Foundation actively encourages local communities to continue growing them. A yam celebration – a community show and tell – which founders Jude & Michel Fanton encouraged in the Solomon Islands resulted in over one hundred yam cultivars being brought together for the first time. The community was surprised at the diversity, and decided to maintain a community conservation collection.
Very few cultivars are grown in Australia. I now have a second winged yam cultivar with purple flesh which I’m eager to trial this year. It was given to me by a keen Brisbane gardener and he reckons it’s as good as the best potato.
You might be lucky enough to find a neighbour, a community garden or a city farm that grows them, but other than that you’ll rarely see them offered. Happy hunting.