In 2008 The Master Gardeners of San Mateo/San Francisco Counties conducted a trial of Andean root crops at their Demonstration Garden at the Elkus Youth Ranch south of Half Moon Bay. One of the crops chosen was Oxalis tuberosa, commonly called Oca.

This member of the oxalis family produces underground rhizomes just as our common oxalis species do, but in the case of tuberosa, the rhizomes are large and edible. Though not well- known in North America, Oca has been grown and eaten for centuries as a staple in the Andean regions of Peru and Bolivia.  It is potato-like in flavor.  The Master Gardeners wanted to see if we could grow Oca in our area, and so we began our trial in the spring of 2008.

After a lot of searching, we obtained Oca seed-tubers from Nichols Nursery in Oregon.  It was the only source we were able to find for the tubers.

On April 22nd we planted 13 of them about 3 inches deep in a well-composted bed at the Elkus Demo Garden.  The beds had drip irrigation and we kept the soil moist. The seed tubers took a very long time to produce shoots above ground.  By June 10th (7 weeks later) only 3 plants out of the 13 had broken the surface of the soil, and when we dug down, we couldn’t find any of the others we had planted. We never knew if the tubers had rotted or had been eaten by something, but we ordered more seed tubers. On June 14 we planted them in potting soil in small pots to sprout, rather that directly in the ground.  We kept them moist and in a sunny spot.  These also took a long time to sprout, but were more successful.

On July 28th (8 weeks after planting the second batch in pots,) we had 7 small starts which we transplanted into a bed in the garden. The plants had the expected clover-like leaves on a rather thick pinkish stem.

The Oca continued to grow throughout the summer.  We experienced no plant diseases or  insect problems.  We did have a terrible time with both deer and bunnies continuing to thwart our efforts to keep them out of the bed.  They seemed to love the taste of our Oca plants.

You can see in this photo that we had a lot of nibbling damage.  And although the bed was lined with chicken wire under the soil, one of the plants was eaten by a gopher. We protected the remaining Oca plants with chicken wire and bird netting to keep the bunnies and deer out. 

By Dec 5th, only 5 of our Oca plants had survived the onslaught of the nibblers.  Those that did survive had grown rather wide with lots of green foliage.  They produced tiny daisy-like yellow blossoms on their tips.  None of the plants showed any sign of disease or insect damage.

We waited until Dec 5th to harvest the Oca because we had read that they should be harvested after the foliage had died back.  However, our plants never really died back, perhaps because of the unusually warm weather we experienced throughout the autumn this year. 

Here is Master Gardener, Laura, getting ready to pull up a large Oca plant on December 5th.

Here is what the Oca looked like as we dug the tubers out of the ground.

The Oca tubers were fat, oblong and shiny, almost waxy. They were mottled red and white in color.  They were wrinkled and slightly bumpy.  They ranged in size from as small as a marble to as long as 5 inches.  From the 5 surviving plants we harvested 4 lbs of Oca tubers.  We left them in a sunny window for 3 or 4 days before cooking them.  This is a practice called “hardening” which allows the tubers to sweeten a bit and to lose some of the oxalic acid which makes them tangy. The Oca can then be stored like a potato in a cool place for consumption later in the winter.

We, however, ate all of our Oca right away.  We scrubbed the tubers under water to remove all of the soil, which came off quite easily.  Peeling was not necessary.  We tossed them in olive oil and salt and pepper and roasted them in the oven like potatoes.  They were absolutely delicious.  The cooked texture was softer than a potato, more like a cooked winter squash.  The flavor was very much like a potato with sour cream already on it....a residual tang from the oxalic acid content.

We kept the very small tubers from our harvest to replant in the spring.  We are keeping them in slightly-moist sand in a cool spot over the winter.  We plan to plant them in early spring and conduct another trial, this time with better deer and bunny protection, so we can maximize our harvest.

The San Mateo/San Francisco Master Gardeners’ Oca trial was a great learning experience, and we are glad to be able to share what we learned with the home gardeners in our community.  The plants are so easy to grow, and most home gardeners will not have deer and bunny issues to deal with.  The tubers are so delicious that we would like to encourage home gardeners to try this unusual crop. It has been a favorite and a staple for so long in South America, and more recently in New Zealand, where Oca has become quite popular and commonplace. The greatest difficulty we encountered was finding where to buy the seed-tubers for planting.  We can direct you to www.nicholsgardennursery.com as a possible source.