The exotic yacón thrives in Estonia too

Harri Poom, Saare-Tõrvaaugu Gardening Farm

Vegetables have been grown for centuries and even millennia, so one would think there aren’t many surprises really left in that department. But that’s where we are wrong! A few years ago, wandering around the Internet on a winter day, a time that is somewhat slow for gardeners, I stumbled upon Smallanthus sonchifolius, or yacón, originating from South America. It is a low-calorie vegetable rich in fibres and great for use in diet food.

The roots taken from the soil, even though really juicy and crunchy, are rather bland in taste. But they turn sweet quickly – a couple of days of withering out in the light, even in direct sunlight, and the yacón roots remind us of fruits; their crunchy texture and sweet juiciness probably bring to mind the Asian pear familiar to us from shops. The roots kept over the winter are sweet already and need no withering.

How to grow yacón?

Even though yacón originates from a place much closer to the equator than we are, the growth requirements seemed to match the Estonian climate nicely: our rather cold and humid summers seemed to be a good fit for the yacón.

So I ordered my first two varieties on eBay (right now, I have 8 already) and they grew very well. The yacón is resistant to diseases and pests and needs no pest control. With its long growth time and sensitivity to night frosts, it is smart to pregrow the plants, otherwise, the yield will be poor. In their first summer, our yacón roots grew in large (a couple of hundred litres) plastic bags and this method worked out very well.

Some tricks we have tried:

• As the yacón picks up growth speed only in the second half of the summer, the plants can be pregrown for quite a while in pots sized a few litres.
• The plants can be planted in the permanent site when the pregrowing pots are too small because the size of the crop mainly forms in late summer and the autumn.
• Pregrown plants may only be planted in beds when there is no more risk of night frosts, so mostly not before the first week of June.
• Yacón can be grown in raised beds, which are good sites for the root.
• The plant takes up a lot of space in the second half of the summer and in the autumn, so the plants should be placed at least half a metre or even more apart.
• At first, there is space for other things to grow in the bed as well, provided that they have a short growing time: various lettuces, radish, dill, onion tops, etc. It is widely known that the plants are often more fruitful and healthier when growing in a mixed bed.
• The yacón root does not need fertilisation if growing in rich soils, but would welcome some compost (or any other organic fertiliser) in leaner and sandier soils.
• It is a good idea to put mulch under and around the plants – the mulch keeps the soil moist and porous, kills any weed and makes the soil more fertile by slowly decomposing. Mown lawn can be used, and even plucked weed – unless the weeding out has been done too late and the seeds are already growing.

The yacón has roots that grow deep and are at the same time very fragile, so the soil needs to be light-textured and at least 30 cm deep. So, raised beds where a suitable surface can be designed are a good choice. In heavier and more clayey soils, there is not much else to choose between than a raised bed or a capacious container (a 5–10 litre container is definitely not enough for the large roots). Thanks to the really juicy roots, the yacón is basically quite drought-resistant, in particular in the second half of the summer when the roots are powerful enough. The soil should be moderately moist throughout the growing time – in dry soil, the yield will be poorer.

Do not rush with the harvesting – the longer the growing time, the larger the yield. But if the tops have already died back, there is no reason to wait any longer. The yacón has storage roots that go deep into the soil, and a rhizome that develops just under the surface of the soil above them. The smooth storage roots are eaten as they have no buds and cannot produce new plants.

To increase the crop yield even more, the plants growing in containers could be taken into the greenhouse in the autumn, if possible, to protect them from the night frosts, and the ones growing in planting beds should be covered with a shade cloth: the tops would be destroyed even in mild cold temperatures and that would immediately stop the roots from growing. Depending on the variety, the agricultural equipment used, and the age of the plant (yes, it is a perennial, and a pot plant can be kept over the winter when there are plus degrees outside), one plant can produce a good few kilos of roots. 3–5 kilos is standard, but it can be even more.

The yacón root is excellent diet food

The yacón root is mainly eaten raw right after peeling. It is a great addition to fresh salads. Its juice tends to turn dark rather quickly, but that does not affect the taste. The roots can also be stewed or boiled – chicken stew with yacón, carrots and onions was a real treat. Yacón is probably not that good in smoothies – or, perhaps only in vegetable and berry mix smoothies that have sour berries or lemon in them.

Regardless of the sweet taste, yacón is excellent diet food and good for both diabetics and weight-watchers. As the sugars in the root appear in the form of fructooligosaccharides (FOS), which are not really absorbed by the body, the yacón is low in calories (15–20 kcal / 100 g) and the glycaemic index is practically zero. Fructooligosaccharides are considered probiotics and have a good effect on the microflora of the digestive system. The yacón root contains 0.3–0.4% of fibre. Furthermore, the roots contain quite a lot of potassium and antioxidants – even as much as ten times more of the latter than a potato does! Supposedly, yacón lowers cholesterol levels and promotes the functioning of the kidneys – but these statements can easily be exaggerations. Even though healthy and tasty, the yacón is no miracle potion. 

How is yacón propagated?

The lumpy rhizome near the soil surface is probably edible as well, but is used for propagating the plant. A plant resprouting from one rhizome bud in the spring will grow a rather large (1–2 kilos is no wonder) rhizome by the autumn, which may have dozens of buds. If there is not much to propagate from, a plant sprouted out of a rhizome piece of about a few dozen grams and having buds will yield a totally okay crop, too. In that case, the pregrowing time is longer, of course, because at the beginning, the transplant will develop slower. If possible, a 2–4 bud rhizome piece of 200–300 grams in weight should be preferred as it will give a good growth spurt to the transplant from the very beginning.

The softwood cuttings made from the early buds growing in the leaf axils also become rooted well enough. Of course, these cannot be harvested in the same year yet, but when kept over the winter in a pot, they will grow faster and will yield more crop than the plants grown from small one-bud rhizome cuttings.

The yacón root blooms late and does not really form a viable seed – most of the seeds are thin. The germinative power of nuttier seeds is also low – 10% is a very good result and usually, it is even lower. So, only plant breeders grow the yacón root from seeds and it is just not worth the trouble for a regular gardener.