Tuesday, 3 August 2010

The All-Tuber Polyculture Mound

In a quiet corner of 'my other plot' I'm trying another cultural method - a four foot wide mound with three different tuber crops grown closely together. I'm aiming for a low-maintenance easily-harvested dense ruck of tuberous productivity.

Unlike standard polycultures, a clear requirement for an all-tuber polyculture is that the crops involved should mature, and be harvested all at the same time, otherwise lifting one will disturb the roots of those remaining.
Oca, Yacon, and Chinese Artichokes together satisfy this criterion quite well, all normally being harvested after their top growth has been killed by frost.
I started in Spring by clearing the area of the previous Jerusalem artichoke crop (yeah, right!), and digging in a barrow-load of rough compost. This was more to improve water retention and aid soil friability (and hence make harvesting easier) than it was to boost fertility. On top of the mound goes one of my prized new variety purple Yacon, purportedly quick-maturing, but so far untried by me. It is certainly much more vigorous than my other 'standard' Yacon variety. Around this goes Oca, then on the outside edge are the Chinese Artichokes.

This little experiment could easily be scaled up to an informal linear raised bed (or 'lazy bed') if one wanted. It could even work on a commercial scale if suitable harvesting machinery was available.

With all the incorporated compost, thorough deep cultivation, and dense weed-suppressing foliage, this is also ideal as a once-and-for-all soil improvement method before turning ground over to no-dig culture.

Drought is the problem this season. All three crops are showing stress, but it will still be interesting to see what quantity of tubers can be got from this single square metre of ground.

Update 31/8/10
The drought has given way to a couple of weeks of pleasant showery weather. The soil moisture, no doubt helped by all that compost in the mound, has caused the Yacon to double in size. It is now seven foot wide and tall, topped with a lanky bouquet of flowers.
It is even suppressing a couple of late-breaking jerusalem artichoke volunteers, and I now fear for the productivity of the Oca and Chinese artichokes.
I either need a smaller Yacon, or a larger mound!

Update 1/11/10
The first air frost on 21/10 burned back the yacon foliage, but has not completely killed it. Under its protective canopy, the Oca plants have escaped damage, unlike those planted on open beds nearby.
A few days before the frost, I noted the yacon had grown to have a spread of nine feet!

Update 12/12/10
There has been freezing weather for a couple of weeks, and the plants are showing no sign of life. It's a dry day, so a good opportunity to exhume the contents of the mound.

First up is the Yacon. It's a big one! The Health & Safety Executive would have me use a hoist for this job, but after a bit of grunting I manage to get the crown in to a wheelbarrow solely by manual handling methods.
After washing, the useable tubers weigh in at 18 lb (8.2 kg), with another pound or two of small or damaged ones.

Delving around nearer the edges of the mound reveals the 'also rans' – a moderate scattering of mostly undersized Oca and Chinese artichoke tubers.
About 1.5 kg in total – which is as much as I can expect given that the plants have been camped under dense Yacon foliage for most of the growing  season.

This growing method was successful in terms of yield and low-labour, despite an unusually early frost. Next year it will be even easier; it will only be necessary to plant the Yacon, as there should be ample volunteer Oca and Chinese artichokes.

The imbalance in yield between the three crop species was caused by misjudging the vigour and final size of the particular variety of Yacon chosen. I mistakenly assumed it would be similar to the 'standard' Yacon that I have grown previously, and as a result the Oca and particularly the Chinese artichokes suffered from lack of light. However, a variety being too successful is a good fault, as they say.

It is an interesting and potentialy useful observation that the Oca were protected from the first frost by the Yacon foliage. Yacon, not being reliant on day length, can tuberise early, before sacrificially protecting undergrowing tender crops which have yet to fully tuberise. The partial defoliation lets through more light to ground level, and as long as there is not a second frost, the lower crops benefit.


  1. I had a similar idea, and I have oca and yacon together in a bed. Unfortunately there are also some volunteer potatoes, but I could wait to dig those up. I hadn't thought of adding in Chinese artichokes, but they're on my list for next year, so thanks for this post :)

  2. Ian, I'm fascinated by your trials, are these things delicious to eat, or is it simply horticultural research for you?

  3. Hi Emma. 'A volunteer is worth ten pressed plants' but only if they are in the right place :)

    Hi CGF. Delicious enough (but there's only one way to find out for sure!). Everything I grow has to pull its weight in the kitchen, and Oca scores a few extra point by being available fresh from the ground in December/January when there is little else available.

  4. Sounds like an interesting arrangement. My guess is that the Chinese artichokes will suffer the most, being quite demanding of moisture. Is the yacon the one I know as "morado"? Purplish tinge to the young leaves?

  5. The Chi-chokes are lowest down on the mound, and benefit most from my watering method - a few wheelbarrow loads of water dumped into the keyhole paths either side of the mound.
    All I know about the Yacon is that it's from the Czech Republic, and it is supposed to mature in 120 days. Yes, there is a slight red tinge on new leaves (photo on 'Yacon doubletake' post shows this quite well. The general leaf colour is much darker than standard yacon.
    It is already flowering!

  6. Hi Rhizowen. Actually, the yacon variety is 'Fiorella'. Soon to be commercially distributed in the UK.

  7. hi, just wondering do you know of any suppliers of chinese artichokes in the uk? i've been on the look out for over a year and still cant find one :/

  8. Hi David. Hmm yes, some companies that I thought supplied them seem, now, not to. However, Marshalls still do them.

  9. Just read about Chinese Artichoke in Gaia's Garden - like your thought on growing several tubers in a polyculture!
    I'm trying to find source of the tubers in US - found one that sells individual plants (know sources for Yacon & Oca) I kept finding UK sources for tubers!

  10. Fascinating,
    thanks for all your research and work, i'll try to replicate some of your stuff !