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 Papua New Guinea. 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.