Now that I am reliably getting oca (Oxalis tuberosa) seed, I’m thinking more about how to improve yields. I lose the majority of the flowers that I pollinate. It is hard to tell at this point, but it looks like I may get mature pods from five to ten percent of the flowers that I pollinate. If I didn’t have more than 300 plants to work with, I might not have collected any seed.
I think that the problem is mostly physical. Oca flowers are small and relatively fragile. We get pretty strong daytime winds this time of year and the stronger the wind blows, the more pods drop. This problem will only get worse as summer continues and daytime temperatures increase inland. The good news is that, if it is a physical problem, rather than a biochemical one, it should be a lot easier to solve. So, I’m going to attempt three mitigation tactics:
|Tags, bags, flowers, and pods all blow away when sustained winds
exceed 12MPH and severe pod loss occurs when gusts exceed 20MPH.
1. Protect plants from the wind.
Where plants are still small enough, I am going to surround them with a 5 gallon bucket with the bottom removed. This should help to block the wind, although the bucket may not be tall enough to stop turbulence. It may also block enough sunlight that the plant responds negatively (by ceasing to flower, for example).
Update: This appears to work pretty well, but armoring hundreds of plants in buckets is not a particularly practical solution. It is an option for protecting the plants with the heaviest pod set in an emergency.
2. Pedicel reinforcement.
I am going to try squirting a blob of expanding polyurethane foam onto the pedicel. It will expand and hold the parts together like glue, reducing the odds that they will separate in the wind. Unfortunately, I suspect that the curing process is likely to damage the stalk. If it doesn’t, it ought to prevent pod drop, although it may simply transfer stress to another point on the plant.
Update: This works very well, but is extremely fussy to deal with. Once the foam sets, no amount of wind dislodges the pods, but dispensing a blob of the right size, keeping it on the pedicel until it dries, and not gluing stems and leaves together in the process is difficult. I wouldn’t want to do it for hundreds or thousands of pods.
3. Move indoors.
I know that other growers have had some success removing the whole inflorescence to mature indoors a week or two after pollination. I don’t think it would have enough energy to mature from an earlier stage. However, it may be possible to cut the entire stem to which the inflorescence is attached and keep it alive in water or sodden soil long enough for the pod to develop. I suspect that when stressed in this way, the stem will drop all the pods, but it is worth a shot.
Update: So far, so good. I took 6-8 inch cuttings and they have held up nicely. They are continuing to flower, which I take as a good sign. Pod drop is reduced to a very low rate indoors. This is probably the most practical and scalable solution of the three – assuming that the pods actually mature.
Oca seeds and tubers are sometimes available in our seed shop.