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Have garden will travel -- growing sweet spuds at home

Maori Sweet Potato Mounds

Now that I have a 'garden' -- in that my underneath is no longer sand and now passes muster as loam -- I get to ponder my horticultural efforts with more focus.

I have ambitions.  I resolve to grow a list of target vegetables  and fruits.

Top of my list: sweet potatoes.

I've grown them for years but not with much success.I've let them ramble and make what they could  of my sandy soil. I've used them to fill spaces and cover ground.

But now I'm serious about my harvest potential so I've been doing my homework.

My initial frustration was harvesting the things. Since I let them travel all over the place hunting tubers was very touchy feely business of inserting my mit in the dirt, fossicking. The truth is that I had too large a 'patch' and needed to focus my growing efforts along demarcation lines.

Most of the literature I've read on sweet spuds isn't very helpful given my conditions. Sweet Potatoes may do best in light sandy soils but that not a sure in from my experience as they also appreciate water and 'light sandy soils' aint water friendly.

But there's a solution in the mix: mounds.  The lit will tell you to raise up your sweet potato plants in order to facilitate drainage. But that's only part of the story.

The traditional method for growing sweet spuds is to cultivate them in mounds.Throughout Polynesia and Melanesia mounds are the means although ridges are sometimes deployed.

 Sweet Potato mounds:Wabag, Papua New Guinea,  1974

A mound is a set space that is easy to tend and harvest from. It can also be deployed to concentrate nutrients.  Research is very clear on the logic. In their study,  Sweet potato cultivation on composted mounds in the highlands of P... Issac T. Taraken and Rainer Ratsch write:

This paper explains the concept of composted mounding, which is used to cultivate sweetpotato/kaukau (Ipomoea batatas) in many locations in Enga province and parts of Southern Highlands and Western Highlands provinces of Papua New Guinea (PNG). It draws both from published literature and recent findings on sweetpotato cultivation in the PNG highlands. The practice of composted mounding allows permanent land use and intercropping, and facilitates successive multiple harvests of sweetpotato tubers and other vegetables. It counteracts the risks of frosts and soil-borne pests and diseases, and reduces soil erosion. It offsets the inherent soil-fertility problems associated with the dominant volcanic ash soils in the mounding zone of the PNG highlands. The method utilises locally available organic materials such as garden debris, weeds, grasses and farmyard manure as compost. 

They further argue:

Potential benefits of composted mounding

There are a number of possible benefits that composted mounds confer. They:

• improve soil texture and structure, thus increasing aeration and rainwater infiltration and drainage

• increase topsoil depth and improve water-holding capacity in shallow and sandy soils, and maintain soil moisture

• provide food and appropriate conditions for soil organisms, and improve soil fertility and crop yield through organic matter decomposition 

• improve soil structure and reduce soil cracking, and the resultant crumb structures probably prevent the entry of pests like sweetpotato weevil (Cylas formicarius)

• maintain soil bulk density in ranges favourable to root penetration regardless of permanent sweet potato cultivation on the same piece of land (Sillitoe 1996) 

• release heat through the decomposition process, which speeds up tuberisation 

• reduce the effects of frosts on crops

• reduce soil-borne pests and diseases, e.g. tuber rot in wet soils or caused by the fungus Ceratocystis fimbriata (Preston 1990; Sillitoe 1996)

• raise crops above water tables in swamps and flooded plains

• reduce soil erosion by run-off both on slopes and flat lands by channelling water between the mounds

• ease population pressure on land use by allowing shorter and even zero fallow periods, and hence permanent systems of land cultivation

• reduce the risk of spreading pests and diseases through the burial of affected crop residues within the mounds

• allow subsequent multiple harvests and the maintenance of planting materials

• enable farmers to use locally available organic residues for sustainable sweetpotato production rather than expensive inorganic fertilisers 

• enable more efficient land use as different crops can be intercropped with sweet potato for subsequent multiple harvests.

A farmer planting sweet potato vines 
on a mound in Tambul, Western Highlands. 

While most commercial sweet potato production uses ridges -- this mound method for growing the spuds impressed me because it more or less utilised a moveable garden -- have garden will travel.

Indeed the protocol meshes with my own attempts to make the best of constructing soil on beach sand. It also deals with the challenge of  allowing for several seasons of fallow in the growing of sweet potatoes especially if your space is limited.

While I've relied on sheet mulching to build my garden I've tended to mulch to uniform thickness -- like a carpet. But mulch mounding is likely to suit some vegetables with potatoes being the best candidate. 

And the great thing is that after harvest you simply move your 'mound' contents elsewhere and grow the next crop in the same place with fresh material inputs collected from wherever.

In effect you get to tame this rambler, facilitating care and harvest. The mounds aren't ant hills -- akin to those you'd associate with normal gardening. These are serious structures. They are in effect garden beds that are not shaped as to our norm. 

How about that for sweet logic? 

This I gotta do. I'm not sure how I'll adapt the business but my next  crop of spuds will begin life in such a home --albeit my best attempt at making one.

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Comment by Dave Riley on May 19, 2014 at 16:50

I have a few varieties underground (maybe 4) but -- as I say -- my soil has not been very productive of tubers so far.But I'm keen --indeed I'm into a tuber fetish at the moment.

At present I'm trying to sprout  some taro and I've now got  myself some (purple) yams ready to trial. Next Sunday I'll mix it with the Islander stalls at the Caboolture Markets and talk tubers.

It's a new ball game in the kitchen with these starches.I'm chasing a dietary preference for safe starches like these.

But sand is shallow fertile (or not at all).So I can only do what my garden allows.

As for sweet spudery you gotta attend the next Pasifika Vibes Festival in Deception Bay. The food is something else. That way you get the core role these tubers play in the cuisine.

And taro oven roast  chips... are wow!

Maybe this is the Landline segment Elaine refers to:Organic Converts...

Comment by Andrew Cumberland on May 19, 2014 at 0:30

I think that if you eat the heck out of the leaves, SP will produce a heap extra roots.  What a bargain!

Comment by Elaine de Saxe on May 19, 2014 at 0:20

Today on Landline (ABC 21, noon Sundays) there was a Sweet Potato grower trialling organics. His fields were in mounded rows - like Strawberries. You would think that there'd be lots of new tubers down the sides of the mounds. He was growing Beauregard the common pink commercial variety which probably grow more quickly than the traditional varieties we grow. And I suppose there's a ready-made collection of rooted cuttings for the next crop.

For the home-grower, the tower system has a lot going for it - much more economical on space and the results are very good.

Comment by Valerie on May 18, 2014 at 22:15

I let my SP ramble and thought I had cleared and harvested most of it only to find out today, a couple of weeks down the line that some SP were sprouting a few meters away from original patch, where they had been allowed to ramble. As I tried to dig the sprouts for transplant and give away I found more spuds in the ground!

I like the idea of a mound and tower for leaves. I need to tame my SP vine all the more so that my chooks have taken voracious liking to the leaves.

Comment by DARREN JAMES on May 17, 2014 at 13:15

Hi mate it was a good read I  sure will try the mound method. have you tried different strains Im sure lots of us growers have cuttings we can share as do I

Comment by Dave Riley on May 15, 2014 at 0:58
Comment by Andrew Cumberland on May 14, 2014 at 22:01

The humble sweet potato is high on my list of great plants.  Thanks for posting this Dave. 

Comment by Vanessa Thompson on May 13, 2014 at 14:01

aha, u have just brought back a child memory of my mum making a few rows, that were mounded up, like ridges of sorts ?  and she would grow her sweet potatoe and potatoes, along this mounds, keeping it growing most of the year {i dont recall them never being there} ...we would push through the sides of the mound, to pick what we needed for dinner, without disturbing the plant so much and leaving it to continue to grow more spuds. { PS: i this is in NZ} 

Comment by Elaine de Saxe on May 13, 2014 at 7:57

Can't argue with centuries of traditional culture.

I have found though, that allowed to ramble, SPs will root at each node and start to form little tubers.

A BLF member, Glenys, came up with the idea of pot culture using a trellis. I can tell you, it works a treat.

Allowing the plants unlimited leaf growth gives a very good yield relative to the small amount of soil used.

The trellises could be used in the field, it's a matter of training the vine to twiddle about the trellis. And you know where the tubers will be!

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