I am always drawn to unusual plants, things I have not grown before and plants I have not heard of. And when it comes to vegetables or edible crops I am a sucker for novelties. When you think about it we have a fairly small range of veg available to us, even smaller when you consider that most of the Chinese cabbages, pak chois and others are basically turnips and that calabrese, broccoli, sprouts and cauliflowers are all cabbages.
So more variety is good. There are two tuberous roots currently making a few waves: yacon and oca, both Central American veg, the first a large, leafy plant with tasty tubers that are crisp and sweet and best eaten raw. Oca is a much smaller plant and easier to grow and keep from one year to the next.
I have grown oca for several years but never had a great deal of success with it and only had twenty or so tubers to bring with me to Ireland and I had never had enough to eat. Oca is a frost-tender perennial in the Oxalis family, in fact it is Oxalis tuberosa. There are not many foodstuffs in the oxalis family, although you can suck on the stems of many native oxalis for the refreshing, lemony taste (though of course they all contain oxalic acid which is not good for you in large amounts). The most obvious edible crop is star fruit, Averrhoa carambola, which looks more exciting than it tastes.
The same can be said of oca too I am afraid. but before we get to eat them we have to grow them. You need to start off with some tubers. Oca needs a long growing season but especially at the end of the season but even so I have just potted the tubers. I put one large tuber or a couple of smaller ones in a 8cm pot, covered with about 2cm of compost and will keep them in a warm, but not baking, spot to get them to sprout. They do not need much heat but they need to be free from frost. Last year I started them at the same time and they were large plants, sprawling around a bit, by the time they could be planted out in late May.
I planted these, about 45cm apart, and they grew strongly all summer in raised beds. They soon covered the ground and knitted together to suppress the weeds. I did have to water them in dry weather but then most other plants needed watering too. They produced a few of the typical, yellow, oxalis flowers in summer but not as many as I expected.
The key to getting a good crop is to keep them growing as long as possible because they do not produce tubers until October and they reputedly form them into November. For this reason this is not a good crop if you live in an area with early autumn frosts unless you grow them in a polytunnel. We had a few light frosts in early November, which didn’t damage the foliage, so I dug up the plants in the second week of November.
I suppose, guessing a bit, that the average crop on each plant was about 200g. This was better than I had ever had before but not fantastic. But I did learn a lot last year.
I found that, although the tubers were fairly easy to clean (you do not need to peel them) they have shallow indentations that are fiddly to clean and my heavy, clay soil was a pain to get out. So this year I am planting them in soil that is heavily enriched with compost. I would be tempted to grow them in pots of compost so they could be put undercover in late autumn if I wanted perfect tubers. I also think they may benefit from some earthing up through summer. Not earthing up as you would potatoes but mulching them with compost. This is because I found that the stems, where they touched the soil, and in some cases where they didn’t, were forming tubers on the stems. I think that, if they were mulched, these might have grown bigger.
The good thing about this crop is that, as far as I can tell, it is free from pests and diseases. Some of the tubers were hollowed out by slugs but that is all. The best and biggest tubers were selected for eating and the smaller ones (hundreds of them) were kept for planting this year.
So, what do they taste like? Well, you can eat them raw and they are pleasantly crunchy and have a sweetish, acidic twang but it does not mask the starchy, raw potato taste. So they are ok raw but nothing great. And I roasted and boiled them. In both cases they do not take long and they should not be overcooked – 15mins roasting is enough. They taste – just like potatoes! I am not sure what I was expecting but they are dull. I think this may work in their favour actually because you can’t really object to the taste and may help them be accepted if anyone starts growing them in commercial quantities.
This is possible and in New Zealand they are reputedly popular and called New Zealand yams. I understand that breeding work is being done to reduce their ‘short-day’ growth response so they form tubers earlier in summer.