Oca: Growing from seed

These are the instructions that I am sending out with packets of oca (Oxalis tuberosa) seed.

These instructions reflect the techniques that have worked for me so far, but I am sure that there is room for improvement.  If you find a procedure that works better, please let me know.

Oca seed does not appear to have any significant dormancy and will germinate without any delay or stratification.

I have started oca seed as late as August and was able to get tubers from some plants the same year, but if you want to grow full size plants and maximize your odds of getting tubers, I recommend starting them a lot earlier.  I’ve found that it takes up to three months to get the majority of plants to two inches tall (after which they grow a lot faster), so in 2014, I’m starting our seeds in December and January, for planting out in late March or early April.

Germinated seed, ready to sow

1. Soak the seeds in water for 24 hours at room temperature.  Don’t skip this step; it more than doubled the germination rate in my test.

Optional :

2. Spread seeds on a wet paper towel, roll up the towel, place it in a plastic bag, and store at 70 degrees F (21 degrees C).

3. Check seeds after 48 hours for signs of sprouting.  A magnifying glass will help a lot, because oca seeds are tiny and you are looking for even tinier root tips.  Check every 24 hours until you see signs of sprouting.  You should see sprouting within a week – probably sooner.

You can skip steps three and four and direct sow instead, but I find it really helpful to know that the seeds are viable before I plant them.  Otherwise, you could be waiting a long time, wondering if anything is ever going to sprout.

4. Surface sow the seeds in containers with any quality potting soil; no amendments are necessary.  I find that up to 30 in a four inch pot works well.

Emerging oca seedling

5. Put the seeds under intense light – either direct sunlight or under grow lights.  I recommend grow lights running at least 15 hours per day for the first month; sunlight provided the same germination rate but slower growth.  Keep the temperature between 65 and 75 degrees F (18 to 24 degrees C).

6. Keep the soil damp.  Don’t let it dry out for the first few weeks.

Within 1 to 2 weeks, you should be able to see the seedlings emerging.  Once a significant number have emerged, remove any supplemental heat.  About 60 degrees F seems to be a good temperature for seedling growth.

7. Once the plants have two sets of true leaves, harden them off and grow them under sunlight in a protected area.  At this stage, plants in sunlight grow faster than those under lights, although you may have no choice but to continue indoors if you have started them early in the year.

Two sets of true leaves; time to move into sunlight

From this point, it is just the same as growing oca from tubers.  I recommend that you keep the plants protected in 1 quart/liter containers until they are about six inches tall.  At that point, the lowest branches will be just big enough to make good cuttings, so you can take a few cuttings to grow as backups while you transplant the seedling to its final position.

In two tests, I got just under 50% of the seeds to the first set of true leaves within three weeks.  Stragglers continued to sprout for quite a while.