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Unusual Vegetables. Oca.

Something new from an ancient culture.

Oca. (Oxalis tuberosa)

Tray of mature tubers at harvest.

This is a vegetable that is causing great excitement amoungst the more adventurous gardeners, and not without good reason. This plant produces tubers in a similar manner to potatoes albiet somewhat smaller. Being of a completely different family to potato it remains unaffected by blight and other associated pest and disease problems.

After this, my first attempt at growing oca in 2007, I can see this as a versatile plant that should lend itself to a number of different growing techniques to suit the grower.

Oca transplant. Mid April.

Growing method.

Seed tubers of oca are difficult to obtain and expensive so the for the first season I started them into growth individually in pots, keeping them frost-free before planting out in late April. Photo to the right shows a young plant after planting.

Plants grow tidily in a neat and upright fashion until the end of July without taking up too much space and during sunny periods will reward you with numbers of small yellow flowers.

Picture of oca bloom.

Most serious gardeners are always short of space and I will mention here that while these plants end up requiring a lot of land, their greatest needs are only towards the end of the season in late Autumn. With this in mind, two new approaches spring to mind that I intend to persue next season. The first is to grow the starters in 2ltr pots until crops such as broad beans or early potatoes are harvested before planting out as a succession crop.

July and the plants are still small.

Another approach would to interplant with upright tall-growing plants such as tomato, sweetcorn etc. or even mixing the two methods. Please bear in mind that I've not yet tested these methods.

Varieties

At the moment there are no proper named varieties although there are several distinct types, each lovingly named according to its skin colour. Tubers shown on this page are the red variety and the other one I grew this season was a pink one. Also readily available is a creamy-white tuber that I will be growing next year. A purple type is known to exist and possible several others but as yet I've not tracked down a source for them.

Oca plants growing in pots, May 08

Summer care

Oca plants after the summer collapse.

Throughout the summer months oca is a trouble-free plant requiring nothing more than an application of manure or fertiliser, watering during dry spells and removing the odd weed as you would with any other summer crop. One thing to be aware of though is that at about the end of July the sturdy upright growth suddenly collapses under its own weight. This had us all worried at first but appears to be a natural habit. The top photo shows a single row of oca in mid August. That's one row not two. The plants are centred in the gap down the middle and the stems have flopped left and right before heading upwards once more.

Mid-Oct and the plants cover the land.

From this point on, the growth is unstoppable with my plants ending up as a thick mound 1.5 mtr accross. Stems that rest on the ground will root quite happily with the foliage becoming lush.

Frost is now the danger and whereever possible, cover the plants to protect them from an early cold snap. Tubers are only just beginning to form now and require as long a growing period as possibe to ensure a decent harvest. It is vital not to get eager to dig them up and they must be left until all top growth dies back with the cold.

Harvest.

Oca root being dug up.

Harvest time is at the very end of November or early December as weather permits when the remains of the stems can be cleared away before digging the tubers. Harvesting should be done when ground conditions are favourable as although most tubers grow under the original planting position, many good tubers can be found all over the place often some distance from the crown.

Yield.

So what do we get for all this trouble?

First year results.

 RedPinkWhite
No. of plants grown.148 
Harvest wt.5kg2kg 
Avg. per plant360gm250gm 
Tubers per plant.5035 

With better weather and growing methods, I believe the average yield per plant could be brought up to somewhere in the region of 1kg per plant, possibly even more making this a useful addition to the more mundane allotment crops.

Kitchen qualities.

Harvested tray of roots.

At the end of the day it is all about taste and usefulness in the kitchen. While the tubers are much smaller than potatoes, they are much easier to prepare. Tubers do not require peeling and the smooth firm skins are easily washed clean. Tubers may be eaten raw, boiled, mashed, fried or roasted making this a versatile vegetable.

And now the question of the decade: What do they taste like? Eaten raw they have a zingy taste and would go well with a salad. I've not had much time to experiment yet but mashed they were delicious and very sweet so this vegetable may be well suited to the more irksome child object.

Once cooked, the red oca turned a creamy-white colour much the same as potato while the pink tubers turned a pale-yellow colour similar to swede. Overall texture was slightly fibrous but nothing extreme. I believe these tubers can become a sought-after delicacy if yields can be improved a little.

Sources.

Currently, the only trustworthy supplier of oca in Great Britain is Realseeds.co.uk.


Jump up to Right column.

Trials for 2008.

With more tubers to play with the focus is on finding the best methods of growing the Oca to produce the maximum yield. Most tubers were started into growth under cover in individual pots but this has proven unneccessary and all future plantings will be direct into the prepared soil.

Oca rows between onions May 08

Growing methods tried.

The majority of the crop was grown in rows spaced approx. 1 metre apart leaving space for two rows of onions in between. Other methods included growing in pots some of which remained in the polytunnel all summer, others put outside for the summer months. Of those placed outside, some were later planted into the soil in early September. Finally there were a few tubers left and a single row were planted direct into a raised hill.

Oca rows after onion harvest Sept 08
Pot culture.

Oca plants grow well in decent sized pots but the crop varied from modest to poor and is not recomended as the way to grow these plants unless garden space is extremely limited. It is fine to grow them on until space becomes available but ideally make sure they are fully planted out during August to ensure a decent harvest.

Crop of Oca from pots grown outside. Nov 08

Autumn care.

Where possible steps should be taken in September to cover the foliage of the Oca to give some protection from early frosts. Tubers do not even start to develop until mid October so require all the help they can to stay alive into November. Tuber growth is fast though once they start.

Another oca patch after alternate crops harvested. Sept 08

Once the plants get a good frosting the tops are killed off and the gardener panics. The plants though have adapted to these frosts and it should not be cause for concern.

Oca in early November after some frost. Nov 08

It is very tempting to rush out the morning after the first hard frost to dig the tubers before they are lost but this is a mistake. The tubers appear to grow rapidly for a couple of weeks after the tops have been killed, drawing down the residual juices from the damaged stems. Be patient and leave them alone. The weather will probably be terrible at this time and grubbing about in muddy soil near to freezing is not an enjoyable experience.

Oca at end of November after severe frost. Nov 08

Best results to date.

This method involved growing the plants on the top of a ridge and while this may look similar to earthed-up potatoes the tubers were simply dibbled into the top of the ridge. There are quite a few variables to eliminate next year before I decide that this is the best way of growing oca but there is one distinct advantage with ease of harvesting.

Oca late December planted on ridge. Nov 08

Anyone growing these will no doubt be aware of the punishment suffered digging the tubers out of wet mud only 1 or 2 degrees above freezing and it is so much easier to shove a fork through the base of the hill, give a quick shake then gather up the harvest.

Oca tubers being harvested from ridge. Nov 08

The ridge was 10 ft long with tubers planted at 9 inch intervals and produced a total of 5.4 kilo of washed tubers. Planting stock was actually the leftovers after the main production had been planted in small starter pots so this harvest was more or less from the rubbish. This amounts to about 2 kilo per sq. metre and if this rate were to be sustained over the whole crop it would become viable. Next year though, I will be aiming at double that return.

Harvest of Oca from the ridge. Nov 08