Design by Sugiyama Tomomi of Ravenart
Permaculture Design & Consultancy
This raised bed construction is an adaptation of the Sheet mulching or also known as Lasagna gardening technique.
The structure is made of rebar sheets normally used for making concrete slabs, doubled with a wire mesh.
Just like composting, the bed is made of several alternating layers of nitrogen rich material and carbon rich material. However once built, the layers won’t be mixed like when composting, allowing for the increase in temperature from bacterial decomposition to drop and leave place to a slow decomposition.
It is recommended to wait for at least a week before planting seedlings in such a bed, to allow for the strong temperatures to dissipate. The warm bed will be a perfect nursery for the new seedling, especially in early spring.
The mesh structure holding the bed upright, allows for plenty of gas exchange within the rhizosphere (the root zone), and helps avoiding water logging during the heavy rains of the japanese monsoon. In western Japan, once the monsoon is over, the region lacks rainfalls and a normal garden if not watered regularly will most likely wither. With this method, virtually no watering is needed, as the different materials act as a sponge in which the roots can tap the required nutrients and water from.
Such raised bed allows for painless maintenance (harvest, weeding) and any weeds sprouting from it is easily pulled out.
Let’s see how the beds are built up.
In this example the soil has been previously weeded, however, one can simply lay sheets of cardboard to act as a weed smother, that will also feed mushroom mycelium with its cellulose, and build rich soil upon decomposition. The materials used and sequence of use in this example, do not really matter, as long as you alternate carbon rich material with nitrogen rich ones, and top the whole thing with soil and/or matured compost for planting your seedlings.
- The first layer used was Ramial Chipped Wood (cf. Ramial Chipped Wood technique by Laval University) a popular technique used in France (called BRF Bois rameal fragmente) that consists of freshly shredded/chipped branches of deciduous trees. 70% of the tree’s nutrients are locked in branches and leaves. Lignin will feed mushroom mycelium that will feed the rhizosphere with micro-nutrients and essential elements, an often missing component in commonly plowed gardens that are normally bacterially dominated. To speed up breaking-down of lignin and fast colonization of the beds with mycelium, a hand full of forest top soil is sprinkled to inoculate the media.
- Next comes a layer of fallen leaves. This too can be inoculated with Indigenous Micro-organisms from nearby forests.
- To trap any leaching nutrients during rainfalls and act as an extra source of carbon, wooden charcoal is sprinkled throughout. This can be repeated as much as one likes. (you can easily make charcoal from bamboo, by burning heaps of it and extinguishing it all before it turns to ashes)
- Then comes the nitrogen rich grass clippings or weeds. Again some Charcoal sprinkling and then a good watering.
- Next comes another layer of RCW, bacterial/fungal inoculum (aka healthy soil), charcoal, and leaves …
- Then comes a good layer of soil mixed with well matured compost (1:1).
- And finally, to imitate a forest soil, a thin layer of humus (sold in garden centers or DIY made from fallen leaves left to decomposed in PP woven bags (reusable) over a year, stacked, watered and turned regularly).
- on top of it all, to retain moisture and prevent erosion and exposure to light, a good layer of mulch.
- In this example, a layer of RCW and grass clippings (weeds) was used.
- Water the whole thing properly and Voila ! you can plant straight away if you so desire, but to avoid any chance of high temperature built-up (depending on the height of your bed) or “nitrogen hunger”, it is wise to wait a week or so.
The best timing for creating such beds is in early spring, when your seedlings will make good use of an extra heat from beneath !
Once a raised bed done, there is no plowing, no mixing, and no more raised bed making. Every weed you pull returns as mulch. At the end of every crop, you cut the stems, let the roots decay and lay the leftover as mulch. Compost and/or urine (or the fertilizer of your choice) as well as plenty of mulch are the only elements added with time.
At the end of a year your raised beds will loose half of their height, as most of the material used have decomposed, leaving you with new space to be filled with compost and mulch..
In this method, as walls are made of wire mesh, weeds (from the seeds in grass clippings) will sprout from the sides. Leave them as is, they will help shelter your crop from wind, confuse bugs, and provide you with easy to pick mulch.
The permaculture design by Sugiyama Tomomi, goes into including a small chicken coop in the center, allowing for each bed to be, on a rotational basis, the chooks playground. The concept of “chicken tractors” serve the needs of both the gardener and the chooks. The gardener needs to control weeds, pests in the soil, and wants more fertility, while chooks need to eat and thus defecate.
The ordering of 8 beds in circle, reminds us of Bill Mollison’s mandala garden, while allowing a theoretical 8 years of crop rotation management. One specific crop will be grown in the same bed every 8 years. Of course in practice there is no need of such a length of time, as most crop will revisit the same beds after cycles of 2 or 4 years.
For more videos on Sugiyama Tomomi’s design in Misumi Ecovillage Saihate, go check out the short documentary realised by NHK, the national broadcasting company of Japan, in spring 2012.