Tuesday, 8 June 2010

Oca / Sweetcorn Bicrop

Various sources state that this is a traditional Andean cultural method, but I cannot find any description of the specific planting patterns used.  They may well have used alternate widely-spaced rows of earthed-up Oca with later-planted corn. But I think corn pollination might suffer from the wide spacing, and the unnecessary soil disturbance and labour does not appeal to me.
I want a method that will suit my no-dig 4ft wide beds, and I think block-planted corn with oca near the centre-line of the bed is going to be the most practical approach for me.

Back on the 25th April the preceding crop of grazing rye was hoed off and removed (for strawing strawberries). Small pot-grown Oca were planted out on the same day.

By the 17th May (below) the Oca are established, but looking very lonely. I never like to see bare soil at the best of times, but continuing cool weather has meant the delayed planting of corn, and the Oca have been on their own for longer than expected. I should have left some of the grazing rye crop-debris on the surface to shade my precious humus and reduce surface evaporation.

Spacing for the corn is the tricky bit. I have a theory that if I can get the corn to support the Oca in an upright position, reducing stem contact with the ground, and thus reducing stem tuber formation, the plants will  be forced to concentrate all of their energy into bigger tubers around the roots (see Tubers- big and few, or small and many), and Oca - Be Erect not Supine!). The corn will have to be reasonably close-planted to do this, but must be far enough apart to admit light to the Oca - a fine balance.

6th of June, the sweetcorn are ready to go...
...and are spaced on a grid of about 1ft across the bed and slightly more along the bed. The Oca sit on the same grid so that each is surrounded by four corn. Just visible are beetroot plugs added along the edges of the bed to complete a three-way polyculture, and utilise the extra light available at the sides.

Plants watered in, paths mulched, there should be no more work until harvest.

Just one week later (13th June), all three crops are putting on amazingly fast growth. Notice the unusually early Oca flower
By the 20th of June, just 14 days after planting the corn, the canopy is about to close. So far, the spacing seems to be working just right, and the weeds won't get a look in.
4th July (4 weeks after planting corn) Stand well back everyone!
Keeping a log with photos and dates really highlights how quickly crops grow in midsummer. The Cylindra beetroot are already of a useable size, the corn is waist high, and the Oca foliage is relentlessly advancing towards the edges of the bed.
We've had consistently hot sunny conditions for the last few weeks, and I think the Oca is probably benefiting from the partial shading of the corn.

23rd July. The corn is above head height and showing signs of flowering. Some beetroot have already been harvested, and the Oca is giving full ground cover to the bed.
Weed suppression is absolute.
With the continuing drought, I've been forced to water a few times, and strong winds flattened some of the corn, so they have been staked, but otherwise the bed has looked after itself just fine.

20th August. The corn is cropping. It's averaging two good-sized cobs per plant, so six per linear foot of bed. The beetroot have all been eaten.

14th September. The corn has all been harvested, and the plants cut back to admit more light to the Oca during the shortening days.

Update, 2010 Oca harvest here.


  1. Where did you get that seed tray? I want a few.

  2. Hi Faith.
    Those are the functionally fabulous, but stupidly expensive Root Trainers, and they are widely used here in the UK for any seedlings that need a deep root run. Peas, beans, sweetcorn and brassicas all do well in them. I would have though that someone would be importing them in to the USA.

  3. That looks like a really good method. Be interesting to see how it develops.

    Rootrainers are fabulous things - as you say, ludicrously priced but there's no doubt that I grow better plants in them than in any other kind of tray.

  4. I've seen Oca in the Organic Gardening catalogue but never tried them, I will have to give them a go, certainly looks like a good pairing with the sweet corn,which I always have to mulch with grass mowings to keep the weeds down. I did try the Three Sisters thing with squash and beans one year but it was a disaster in my garden, this looks much better.

  5. CGF, The success of the Three Sisters thing is down to timing - squash gets too big and kills corn - corn gets too big and kills beans - squash gets too big and kills beans - there are lots of ways to get it wrong.
    But then this method could also have gone wrong. I think I've been lucky - if the corn was planted earlier it could have slowed the development of the Oca by cutting out the light.
    Are you sure Organic Gardening Catalogue sell Oca? (not to be confused with Okra, which they do sell).
    Remind me around January, I'm sure I'll have a few tubers for you to try.

  6. Great site, growing needs more (publicly available) analytical study.

    How good was cross pollination and kernel formation on the corn? were there missing kernels?

    What was the spacing? about 10 inches per plant?


    1. Thanks Paul. I'd say 10 inches would be a bit close, shading out the oca bicrop. It looks more like 12 to 14 inches to me (that's a 4ft wide bed). Pollination was complete as far as I remember. Certainly I would expect no problems at that spacing.

    2. Thanks for the reply. I'm planning emulating this pattern this year and may add additional support with short canes around the oca.

      After searching on your blog it appears oca doesn't like nitrogen feeds later in development...I'm assuming this is to stop more top growth and focus on the tubers. Am I right in assuming that a nitrogen supply to the corn in the oca's earlier development wont have an impact on the tuber yields later on? Could it possibly benefit yields?

      I feel that it may be good for tuber development when providing an early supply of nitrogen long before the first frost, I feel like aiding larger top growth early on would be beneficial later when the energy is driven down from the foliage to the tubers themselves.

    3. Paul, I'd say you are accurate with those assumptions. Corn, of course is a hungry feeder benefiting from plenty of nitrogen, however surplus nitrogen late in the season may adversely affect oca's frost tolerance.