A FOOD WALL FOR ARID REGIONS, COMBINING SACK GARDENING WITH LIVE NAVAJO WILLOWS
The numerous advantages of sack gardening and growing drought-tolerant Navajo willows have been described earlier:
(a) Sack gardening
Recently, I was discussing opportunities to grow fresh food in an arid environment – see DESERTIFICATION FIELD PRACTICES
We suggested to combine both methods/techniques (sacks and live trees) in order to solve a number of classical problems: drought, limited quantity of irrigation water, heat, UV-radiation, etc, killing different birds with one stone.
Taking into account that, at the global level, urban population is continuously growing, and that all these people lack some basic skills and resources, like agricultural or horticultural knowledge and experience, land tenure, funds, etc., there is an urgent need for enhancing their food production’s potential by teaching them very simple, but effective ways to grow food in small spaces of the urban or rural environment.
In January 2011, I have been reading at the blog of WORLDWATCH / ‘NOURISHING THE PLANET’:
“In Kibera, the largest slum in sub-Saharan Africa, located in Nairobi, over 1,000, mainly female, farmers now grow food quickly and in small spaces by filling tall sacks with soil and poking holes on different levels to plant seeds. These “vertical gardens” helped Nairobi families survive when unrest after the 2008 elections shut down roads and prevented food from coming into the cities. Growing food for their families and selling the surplus also helps people improve their diets and livelihoods. …………………………. And urban farmers are finding innovative ways of growing food when they don’t have access to soil and other natural resources. With help from the Education Concerns for Hunger Organization (ECHO) farmers are taking advantage of trash by creating gardens from old tires, which they cut in half to use as gardening containers. Chapter 10 in State of the World 2011 explains how farmers can use old cans, plastic bags, and other garbage, along with organic waste, to grow food in these planters, which can be used on rooftops and moved around easily when space is tight. And these are just the beginning. Do you know of any other innovative projects that are working to help urban farmers?
A nice photo of Bernard POLLACK was added, showing how successful sack gardening can be.
In 2008, the Lebanese-born artist Mona HATOUM created in Berlin an artwork called “Hanging Garden”, described as follows: “………..her ‘hanging garden’ consists of 770 jute sacks, stacked to head level. All together, they form a 10 meter long wall, which looks much like the sandbag barricades used as defense from enemy gunfire during battle and other war zones such as checkpoints and border crossings. Despite the associations we have with the image of these barricades, the sacks are filled with seeds that sprout, greening the wall and expressing more of an image of growth and prosperity. The piece deals with the friction between notions of home, security, warmth and their opposites.”
Some photos are published at:
An outdoor version of such a “Hanging Garden” was seen in Vienna in 2008-2009 (http://www.vvork.com/index.php?s=hatoum)
(b) The Food Wall
Mona HATOUM’s splendid artwork and the positive news about people in Nairobi, combating hunger and poverty with “sack gardening”, brought me to the idea that it must be possible to build a vertical vegetable garden as a Food Wall of stacked burlap (jute) sacks, filled with a mixture of dirt (soil) and manure. Adding a water absorbent soil conditioner (if cost is not a limiting factor!) can enhance the water retention capacity in the sacks.
Burlap’s rugged strength, tailored for packaging up to 60 kgs of weight, and its low cost make it an ideal textile for this gardening purpose. It resists weathering and stands repeated wetting and drying with minimum loss of strength.
One can build such a Food Wall according to the local possibilities (available space, height, width, dimension of sacks, available irrigation water, available seeds, …).
In order to construct a strong wall, resisting the strongest winds, two rows of sacks should be used. One single top row of sacks can be put in the middle over the separation line between the two rows to link the two parts of the wall (see photos above).
If the Food Wall can be watered with a hose, the sacks can be stacked to head level, e.g. 180 cm (6 ft) high. On the contrary, if the wall has to be hand watered, it should be maximally 150 cm (5 ft) high, so that a watering can, bucket or pot can be used to poor water over the top layer of sacks. Rain also penetrates quite easily in these sacks, thus contributing to the management of this Food Wall. Annual rainfall will be an important factor for determining the volume of irrigation water needed to keep the vegetables and herbs on this wall alive.
Once the wall erected at the desired dimensions, it should be watered thoroughly to create maximal soil moisture inside the sacks. Water will slowly percolate from top to bottom, from sack layer to sack layer. This can take a couple of days, but once completely moistened, the soil in the sacks will remain humid for a very long period, evaporation rate being relatively low due to the protective function of the jute.
Now time has come to cut small openings in the jute wall of all the sacks, preferably with a very sharp knife. These openings can have the form of an X or of a simple horizontal slit. One has to choose the number of openings, their dimension and their location on the wall in function of the plant species, its growth pattern, its ultimate dimensions and the way the plants are harvested (leaves, stems, roots, tubers, the whole plant, …).
Seedlings or young plants of vegetables and herbs are planted directly in the openings. Seeds are sown in the horizontal slits, of which the length has to be adapted to the nature of the adult plant (but not too long to keep the sack’s strength at a sufficient level, avoiding that some soil slides away).
Due to transpiration of the growing vegetables and herbs, and some evaporation through the jute wall of the sacks, a small quantity of soil moisture will be lost gradually. This can easily be replaced by watering the columns of drying sacks from time to time. Some columns will dry sooner than others. This will also be the case for the sunny (south ?) side of the wall.
Tall plant species should be planted at the lower parts of the Food Wall, smaller ones closer to the top. Horizontal alternation of plant species can help to create a distribution pattern over the wall, offering sufficient sunlight to all the individual plants. It goes without saying that some experience has to be gained by anyone to obtain maximal results.
A friend suggested “to do a project that erects rammed earth walls in the desert with vertical gardens on their north side, do the monitoring and show that you have 50% less evaporation losses that way”. This reminded me of the fact that the orientation of a Food Wall can be an important factor too: dominant wind direction, shadow, …
And precisely the factor shadow brought me to the idea that the above described Food Wall can easily be combined with growing Navajo willows.
(c) Navajo Willows
At home in Belgium, I have been experimenting with an extremely interesting tree species, the lime green Globe Navajo Willow (Salix matsudana), known as a fast growing, very hardy, large, deciduous tree, native to northeastern China. In the southwestern United States, the ‘Navajo’ cultivar has been selected for its drought-tolerance and storm damage-resistance.
Semi-hardwood cuttings and hardwood cuttings are used for rapid propagation, e.g. in xeriscaping. I grew it from a small semi-hardwood cutting into a splendid 30 ft (9 meter) high, globe-shaped, upright branching tree in 9 years time. It is said to be a long-lived tree species, adaptable to a wide range of soil conditions. It already resisted several years of winter frost in my own garden without any damage.
Aiming at creating in the drylands shady spaces, to be used as a live greenhouse (or in which people could rest!), I have set up an experiment called “tipi live greenhouse”:
This experiment convinced me that the Navajo willow merits full attention for its application potentials in all the drylands of this world.
One of its applications would be to plant one or more willow cuttings on the spot where later on a Food Wall will be erected. Once the cuttings are rooted and young willows are high enough (180-210 cm/ 6-7 ft) the sacks can be positioned around the stem, leaving sufficient opening for the stem to expand its diameter in the years to come.
Considering that an adult tree is growing up to 25-30 ft (8-9 meter) high and that its round-headed canopy reaches the same width, one single Navajo willow could cover an entire Food Wall. Therefore, only one Navajo willow would suffice to filter the bright sunlight of the drylands and to offer a light shadow over the Food Wall to enhance vegetable and herb production on the sacks.
Meanwhile, the Navajo willow will also profit from the irrigation water used for the Food Wall, a small part of that water reaching the soil underneath.
We are actually looking for interested people to set up a Food Wall-experiment in their own environment, combining sack gardening with one or more live Navajo willows. We would warmly welcome illustrated reports (with photos and legends) on the progress made and experience gained with different vegetables and herbs. Who wants to join our “global” experiment?