Water Powered Hammer (Monjolo)

I built a water powered hammer called a “Monjolo”. I started by making a water spout from half a hollow log to direct water from the creek. This was set up in the creek and water flowed through it. The hammer was made from a fallen tree. I cut it to size by burning it at the points I wanted it cut (to save effort chopping). Next I carved a trough in one end to catch falling water. This was done first with a stone chisel that was then hafted to an L–shaped handle and used as an adze. This adze only took about an hour to make as I already had the chisel head and cordage made of bark fibre to bind it with.

To save further effort carving I used hot coals from the fire to char the wood in the trough. I put the coals in using “chopsticks” (unused arrow shafts) to transfer them from the pit. The coals were fanned or blown with a wooden blowpipe till the wood in the trough burned. Then the char was scraped out. The sides of the trough were sealed with clay to make sure the wooden sides did not burn away which would effectively decrease the volume of the trough. This was approximately 8 hours work over two days.

With the trough carved I made a hole in the middle of the log as a pivot point. Using the same char and scrape method I burnt a hole right through the log using hot coals and a blow pipe. Again clay was used to prevent wood burning where it was wanted. To burn through the approximately 25 cm diameter log it took about 4 hours and 30 minutes. Another hole was burnt in the end to fit the wooden hammer head and it took a similar amount of time.

A tripod lashed with loya cane was set up at the water spout. The axel of the hammer was tied to one leg, the hammer fitted onto the axel and the other end of the axel tied to another leg. The trough was positioned under the waterspout to collect water and the tripod adjusted so that the resting point of the hammer was horizontal (so water wouldn’t prematurely spill out of the trough).

The trough filled with water, outweighed the hammer head and tilted the hammer up into the air. The water then emptied out of the trough (now slanting downwards) and the hammer then slammed down onto an anvil stone returning to its original position. The cycle then repeated at the approximate rate of one strike every 10 seconds. The hammer crushes small soft types of stone like sandstone or ochre. I carved a bowl into the anvil stone so that it would collect the powder. I then crushed old pottery (useful as grog for new pots) and charcoal. Practically speaking, this hammer worked ok as a proof of concept but I might adjust it or make a new one with a larger trough and bigger hammer for heavy duty work.

This is the first machine I’ve built using primitive technology that produces work without human effort. Falling water replaces human calories to perform a repetitive task. A permanent set up usually has a shed protecting the hammer and materials from the weather while the trough end sits outside under the spout.  This type of hammer is used to pulverise grain into flour and I thought I might use one to mill dry cassava chips into flour when the garden matures. This device has also been used to crush clay for porcelain production. A stone head might make it useful as a stamp mill for crushing ores to powder. It might pulp fibres for paper even.

Termite clay kiln and pottery

I built this pottery kiln and some pottery from termite mound clay to test an alternative clay source to my usual one from the creek bank. I started by making a large grate from ordinary clay. It was just under 50 cm in diameter. Next, I took dry chunks of termite nest and put them into the pit in front of the tiled roof hut. The chunks were crushed and water was added to slake the clay. The clay was trodden on to mix it. Dead palm fronds were added to the clay to stop it from cracking as it dried and to add insulation to the kiln. The mixture was trodden on again and then taken from the pit. A trench was dug to form the firebox of the kiln and a wall of clay was made in the front of the trench. A hole was dug into the wall to allow air flow into the firebox.

The grate was placed on top of the firebox and the walls of the ware chamber were built around the grate. When the kiln walls were finished, grate bars made from termite clay were placed into the firebox. Grate bars are important for fireboxes as they lift the firewood off the ground allowing air to move up through the fuel bed for more efficient combustion. Burning wood as a heap on the ground allows cold air to flow up and over the coals, cooling the kiln and leaving the air unreacted with the fire wood. It still works but is much less efficient than using grate bars. The finished kiln was 50 cm tall (above grate height), 50 cm in diameter and with walls about 12.5 cm thick. The pit/firebox was about 25 cm deep and 25 cm wide with grate bars sitting half way between the ground and the circular kiln grate above.

Next, for the pottery clay, I selected a termite mound built on red clay soil. I took it to the kiln area and slaked it with water and mixed it in a small pit. I crushed up an old grate from a previous kiln and mixed it into the termite clay as grog. Grog prevents pottery from cracking as it dries and helps prevent breakage when firing. I then shaped the clay into a small urn. I also made some barrel roof tiles and a smaller pot from termite clay. I then stacked the kiln with the termite pottery (the urn, small pot and 5 barrel tiles) and some pottery made from normal clay (the housing for the forge blower and 2 barrel tiles).

To fire the pottery, I collected a large pile of dead wood and started a fire in the firebox. I heard some explosions in the kiln early on and knew something broke but continued anyway. To prevent explosions you should make sure all the pots are completely dry and slowly heat the kiln. Within an hour the kiln had heated up well and the pottery was glowing red hot. By the second hour the temperature went down illustrating an important point: if you over fill the firebox with wood the kiln will choke it and not burn efficiently. Realising this mistake I merely let the wood burn down a little so more air could get through. It’s important to watch the inside of the kiln and see how hot it’s glowing, try adding more or less wood and observe the effect on temperature. By 2 hours and 30 minutes the kiln was firing nicely again with all the pottery glowing low orange (about 845 c or 1550 f). I kept it at this low firing temperature for another 30 minutes. The whole firing process took about 3 hours from start to finish, a relatively short period of time for firing pottery.

When I took the pottery out, one tile had broken and the urn had spalled (a piece of the outer pot broke off) possibly due to still having moisture in it. The urn was still useable though and I use it to water the cassava patch. The forge blower was well fired and is now immune to water damage, no longer needing to be carefully protected from the rain. I put it in the barrel tile shed for storage. I put the broken tile and spalled piece from the urn in a special heap of broken pottery. When I make pottery in future I can crush up these broken pots and mix it into the new clay as grog to strengthen the new ceramic items. Finally, I stored the good tiles at the barrel tiled hut as replacements for broken tiles in that structure should there be any damage in future.

Termite clay is good material for making furnaces and an OK substitute for good pottery clay should it be difficult to find a better source. The termites have already processed the clay by the fact that their mouths are too small to include sticks and pebbles into their structures. As a result, the clay is very smooth and plastic. Too smooth for my liking, in fact, I’m used to working with coarser clay that has silt mixed into it naturally. I find that termite clay is either too runny when wet or cracks too easily when drier. It was difficult to form into complex shapes and it took me 2 attempts to make the urn. But for forming objects like tiles it’s OK, it can be pressed into shape and it will hold without difficulty. In future, I’d be likely to use termite clay for mass producing formed objects such as bricks, tiles, simple pots (formed over a mould) and possibly pipes, thereby conserving the dwindling clay supply from the creek bank which I’ll save for more intricate pottery. In summary, termite clay is able to be used to produce basic pottery if no other source can be found. If you have a termite nest you can make basic pottery from it.

Planting Cassava and Yams

In this video I build a garden to grow Cassava and yams, two staple food crops. Cassava is a shrub that develops large edible roots. Yams are a climbing vine that produce large, edible underground bulbs and smaller aerial bulbs on their vines.

I had 5 huts, but the wattle and daub hut (from the first video uploaded on this channel nearly 2 years ago) became dilapidated. I abandoned it in favour of the other huts I built and neglected the roof. This let water in destroying a wall. Also, the sweet potato patch behind it had a tree fall across it destroying the fence. So I demolished them both to make one large garden.

After removing the fence I set a fire under the fallen tree to burn it in half rather than spend the effort of cutting it with stone tools. After burning almost all the way through, it rained. So I came back later and cut through the rest of the log with stone tools. I eventually broke the tree in half. Using smaller logs as levers I moved the tree out of the garden clearing the space for the garden.

I then collected wood and built a simple fence that was woven loosely together with vine. The fence needs only to discourage large animals from entering to prevent them causing damage. Most times pigs and wallabies don’t know that food in growing in the garden and won’t try and enter if they see no reason to. Or at least that worked for the sweet potatoes so we’ll see if it works this time.

For the yam and cassava planting material I travelled far down stream to the site of my old stone hut that I built over 10 years ago. It had a corbelled dome roof that was damaged when a tree fell on it during a cyclone and it came down a few months later. The thick walls however have stayed standing for about a decade though.

Yams and cassava grew wild at this site which is one of the reasons I built the stone hut there. These plants are not native to Australia but grow wild here after having escaped from people’s gardens (similar to how wild pigs live here now after escaping from farms). The planting material for the yams are the bulbs that grow on the vines. The planting material for cassava are simply 25 cm long pieces of stem.

On returning to the garden, a scrub turkey was seen digging in the mounds. Protected by law, this bird has lost its fear of humans and in this case I’ve semi-domesticated it. Originally it was attracted to soil I dug up for the worms it exposed. I started leaving a pot out with small sweet potatoes in it for it to eat and now it investigates any pottery I leave for food. Now it my visits my projects and will only leave if bored or chased away. I suppose this is similar to how chickens were domesticated, in fact bush turkeys and chickens are related and will produce hybrid offspring.

Unfortunately, it has learned that the garden contains food. Originally, I was only going to plant yams but I saw the turkey digging them up and eating them. So, I planted cassava in the mounds so that the turkey would be discouraged by finding only wooden stems to peck at. I secretly planted the yams along the fence of the garden because the turkey only thinks the mounds contain yams. They can’t smell very well and only find food by sight and learned behaviour.

I planted the cassava in mounds 1 meter apart by pushing them flat into the soil. I planted the yams at intervals along the fence so they could use it as a trellis. 32 cassava stems and 12 yams were planted. Then a storm began and watered the garden. In less than a week the cassava had sprouted shoots and began to grow. The yams will take longer as I planted them deeper.

Cassava produces the most calories per time and space of any plant apart from sugar cane and sugar beet. But it requires much less fertiliser and effort. A hectare of cassava produces enough calories in 2 days to sustain a person for 1 year. It takes a year to come to harvest but will stay in the ground for a year without becoming woody. The tubers are high in starch and are what tapioca is made from.

This variety is called sweet cassava (actually not bitter cassava, it doesn’t taste sweet but starchy instead) and it needs to be boiled for 20 minutes to get rid of some cyanide it contains. The bitter variety contains such high levels that it kills if eaten raw and requires more extensive treatment to eat. There isn’t much nutrition in cassava other than the large amount calories it contains so other food would be required to provide protein and nutrients.

After I harvest the cassava I planted I’ll try fermenting it (which adds nutrition), drying it and pounding it into flour to make flat bread. Cassava flour has the same energy content as wheat flour, stores well and tastes somewhat similar. Or I could just cook it and eat it straight from the garden. I’ll use the yams like potatoes when they’re ready.

Bed Shed

I built a bed shed, a small shelter with a sleeping platform built into it. It’s quicker to build than a large hut but can be extended later on when materials and time become available. It’s not far from the dome shaped grass hut I built earlier.
The hut is 2 m long and 1 m wide. Four posts were hammered into the ground, two 1 m high posts (1.25 m long, 25 cm underground) on the low side and two 2m high posts (2.25m long, 25cm underground) on the high side. Onto this, a sloping rafters was lashed on with fish tail wait-a-while, a spiky palm with a vine like habit. To remove the needle like spikes from the plant, the leaves are pulled off so that the frond sheaths come with them. This made suitable lashings.
Battens were then tied to the rafters and bundles of long grass from the mountainside were collected. Using vine from the bush, the bundles were lashed to the battens starting at the low side and continuing to the top so that the grass would shed rain. Cross bars were lashed to the frame of the shed at each end to support the bed. These were at a height of 1m above the ground.
The bed frame itself was made from four poles (two 2m long and two 75 cm long) lashed together to form a rectangle 1.75m long and 75 cm wide (the ends of the two longer poles extending further to sit on the cross bars in the shed). Lawyer cane was then wrapped length ways over the frame to create horizontal threads. Then more lawyer cane was woven between these threads to form a sort of bed spring net. The bed frame was then put on the cross bars and tested to see if it could hold my weight. A mat I made from woven bark in a previous video was used for bedding and a bunch of grass for a pillow. In a rainstorm it was possible to make a fire in the space under the bed.
This structure is quick and easy to build. The bed is 1 m above the ground and provides plenty of area beneath to store fire wood and tools out of the rain as well as a place to sit and make things. The bed is comfortable and keeps the occupant off the ground away from ground dwelling creatures at night. The smoke coming up from the fire keeps mosquitoes away while providing heat and light reflected back from the roof. In fine weather the fire can be placed in front of the shed in the open while during rain the fire can be kept under the shelter to keep it dry. If room is needed to stand up the bed can be folded up against the roof and tied to it using cordage.
This shed is literally one half of the standard rectilinear hut I usually build (2m x2m floor plan, 2m tall ridge line and 1 m high side walls e.g. from wattle and daub hut and tiled hut videos) and was built to be upgradeable. Later, the other side of the roof could be added on and then walls of some kind built around the frame to form a full hut.

Fresh water Prawn Trap

I built a prawn trap from lawyer cane, sticks and vine. Then I caught some prawns and ate them.
Prawn (and fish) traps are simple traps designed to catch aquatic life due to their shape. It consists of a simple basket with a funnel shaped entrance. Prawns easily find their way into the trap as they are funneled in, but have difficulty finding the way out.
I wove the main body of the trap from lawyer cane then made the funnel from sticks with vines woven between them. The funnel was then inserted in the top of the basket and was complete.
I put the trap in the water under some tree roots without any bait. About 10 minutes later caught the first prawn which I stored in a pot of water. I caught another one and made a fire.
I humanely killed the prawns using the splitting method which destroys the central nervous system (boiling alive is more painful). Then I put them back in the pot with water. I collected some yams that I planted years ago from wild stock and put them in too.
I took 5 hot rocks from the fire and put them in the pot boiling the contents. The prawns turned red after cooking. They were peeled and eaten. The yams were also peeled and eaten.
This method of catching prawns is easy with the only skill needed being basketry. In practice, a long stretch of creek might have several traps collecting food each day without any effort on the part of the fisherman. Bait is not necessary to catch prawns as they will be naturally be drawn to the fish trap out of curiosity. But scraps from previous prawn may be used to bring in new ones (they are cannibalistic) or other fish like eels. The prawn trap is easy to build and can be reused many times.

Edit: This is a prawn and not a shrimp as I originally called it. Here’s the difference: https://museumvictoria.com.au/discoverycentre/infosheets/what-is-the-difference-between-prawns-and-shrimp/.

Spear Thrower

A spear thrower is a simple tool that allows the user to throw a spear further than by hand alone. It is a small length of wood with a hook in the end that fits into a notch in the back of the spear. The extra power and distance gained by the thrower is due to the extra leverage it gives.

I cut a small branch with a minor branch coming off the side. I shaped the minor branch into a spur to fit into the end of the spear. The thrower was about 65 cm long.For the spear, I cut a thin sapling approximately 2 m long and about 1.5 cm thick. I carved a cup in the end of the spear for the spur to fit into. Then I bound the back of the spear with bark fiber to prevent the wood from splitting. The head of the spear was simply charred in the fire and scrapped against a rock to sharpen it (during practice the head regularly breaks so only a sharpened tip is used to save work).

To use the spear thrower, the spur of the thrower is inserted into the cup of the spear. The spear and thrower are held at about shoulder height. The thrower is quickly flicked forward and the spear propelled towards the target. As the spear leaves the thrower it bends slightly storing energy until it jumps of the spur. During flight, the flexible spear wobbles and oscillates paradoxically giving the spear some stability in flight.

The throws in the video show what can be done in one afternoon of practice (my arm got sore and I wanted to start on other projects). I hit the target a few times at a distance 15 m. It is more powerful than a spear thrown by hand alone but is difficult to learn. The spear I made could have been a fraction lighter and so would have greater speed. Another improvement would be to add flights to the spear so it would be more accurate and fly straighter (like an atlatl).

The extra energy gained from a Woomera’s (Australian spear thrower) use has been calculated as 4 times that of compound bow (Wikipedia). It’s easy to make (this took less than a day) but requires lots of training to become accurate.

Barrel Tiled Shed

I built a tiled roof shed to provide a fire and rain proof shelter for working on projects during wet weather and for storing firewood. The shed houses the very kiln used to fire its own tiles.

I cut timber using the stone hatchet and took it to the building site. 6 Upright posts were stuck into the ground about half a meter. Mortices were cut into the horizontal beams using a stone chisel to start with, then had there mortices enlarged using hot coals and a blow pipe to burn them out more. These beams were put in place and rafters were lashed on with lawyer cane. The wood that the tiles sit on are about 50 cm apart. The finished frame was 2 x 2 m in floor plan, 2 m tall at the ridge line and 1.5 m tall at the sides. This roof angle is about 22.5 degrees, half the pitch of the huts I usually make. This took about a week but I did it about 4 months ago and left the wood at the site because I was busy on other videos

Next I made a kiln. I made a basket to make it easier to carry clay from the creek. I dug a trench for the firebox of the kiln and made a clay vault over it using stick arches to support it. Holes were put into the vault to let flames through. The kiln shape was a cube with a domed roof. It was made of mud on site (clay from the creek is too good to build a kiln with and is best used for pottery). Grate bars were put into the firebox to increase wood burning efficiency by letting air come up through the wood rather than over it. This only took about 3 days to build letting it dry slowly.

To make the tiles, clay was collected and had the sticks and stones taken out of it. Then I crushed up old broken pottery and tiles I made before which I mixed with the clays as grog (stops clay from cracking). A tile frame was made from a split piece of lawyer cane bent into a trapezoidal shape about 50 cm long, 20 cm at the wide end and 16 cm at the narrow end. This was put on a flat stone. Wood ash was put down to stop the clay sticking to the rock. The clay was pressed into the fame and the wet tile was slid onto a curved piece of wood to form the curved shape of the barrel tile. The tile was then moved immediately to a flat area and the piece of wood was slid out so the tile sat on the ground to dry. Being curved, air could get under the tile to help dry it out.

I could make 30 tiles easily in a day and only had 150 to make. But it kept raining and destroying the tiles before they dried. So I had to make 30 tiles, let them dry enough to be moved, then take them to the tiled hut where they were force dried on the ondol (fire heated bed). The majority of the time spent on this project was re-making broken tiles due to unseasonal rain (I don’t think we have a proper dry season here anymore, this is what held up my other tiled hut too). So this whole part probably took 4 weeks.

Firing the tiles was easy compared to the other tiled hut I built. I could fit 30 tiles in the kiln at once and had 150 tiles to fire. The 5 firings took 5, 4.5, 3.5, 4.5 and 3.5 hours. The first one probably took longer due to the kiln not being dry yet and the 4th firing took a while due to wet firewood. Tiling the roof was also easy. Starting at one end, tiles were laid so that the concavity faced up and the narrow end pointed into the next tile below acting like a shoot for water to run down. The gaps between these tiles was covered using a tile with the concavity facing down and the narrow end pointing up under the next tile above. The ridge of the hut was covered with the same tiles interlocking to keep rain out. The low roof pitch, the weight and friction of the tiles, the fact that they interlock all help to keep the tiles in place meaning they don’t need tabs or pegs to hold them in place.

The roof sheds rain and is fireproof. This will provide a workplace for fire related projects in all weather. Walls were not built as this is a place for working and storing firewood, not sleeping and staying warm. Also, light can come in so it’s easy to see during work. The kiln worked ok and was able to handle a larger volume of tiles than the previous kiln I built (having over 4 times the volume) though I might investigate better kiln designs in future to attain higher temperatures and use less firewood. The roof of this shed has a lower angle to my other huts meaning it has more headroom. Ideally barrel tiles should be used at about 30 degrees as opposed to the 22.5 I used but being a small shelter I don’t think the water will build up and seep through. A large house would use a slightly steeper angle.

Forge Blower

I invented the Bow Blower, a combination of the bow drill and forge blower to make a device that can force air into a fire while being easy to construct from commonly occurring natural materials using only primitive technology. I began by fanning a fire with a piece of bark to increase its temperature. It is this basic principle I improved on throughout the project.

Next, I made a rotary fan from two pieces of bark that slot together at right angles to each other to form a simple 4 bladed paddle wheel about 20 cm in diameter and 5 cm tall. The blades of the fan were not angled and were designed only to throw air outwards away from the axle when spun. The rotor of the fan was made by splitting a stick two ways so it formed 4 prongs. The fan was then inserted into the prongs and the end lashed to hold it in place. Spinning the fan rotor back and forth between the palms of the hands fanned the fire. But only some of the wind generated by the fan reached the fire. The rest of it was blowing in other directions, effectively being wasted.

So I built a fan housing from unfired clay to direct the air flow into the fire. This was basically an upturned pot with a hole in the top, a spout coming out of the side. The housing was about 25 cm wide and 8 cm tall. The hole in the top and the spout were both about 6 cm in diameter so that the air coming in roughly equalled the air coming out. The base of the fan rotor sat in a wooden socket placed in the ground to make it spin easier and the top of the rotor protruded from the hole in the top of the housing.

Now when the fan spun, air entered the hole in the top of the housing and exited the spout in the side. Importantly, it doesn’t matter which way the fan spins, air always goes into the inlet and out the spout. Air is thrown out towards the walls of the housing and can only leave through the spout while the vacuum in the centre sucks new air into the housing through the inlet. A separate clay pipe called a tuyere was made to fit over the spout to direct air into the coals. This was done because the pipe that touches the fire can melt away so it’s better to make this part replaceable.

Instead of making a large wheel and belt assembly to step up the speed of rotation, I opted for a 75 cm long bow. I made a frame to hold the rotor in place consisting of two stakes hammered into the ground with a socketed cross bar lashed on to hold the top of the rotor. I made bark fibre cordage and tied the end to a stick. I then looped the cord around the rotor and held the other end in the same hand holding the stick. I then pushed and pulled the bow causing the rotor to spin rapidly, forcing air into the fire.

I made a simple mud furnace for the blower. Then I collected orange iron bacteria from the creek (iron oxide), mixed it with charcoal powder (carbon to reduce oxide to metal) and wood ash (flux to lower the meting point) and formed it into a cylindrical brick. I filled the furnace with charcoal, put the ore brick in and commenced firing. The ore brick melted and produced slag with tiny, 1mm sized specs of iron through it. My intent was not so much to make iron but to show that the furnace can reach a fairly high temperature using this blower. A taller furnace called a bloomery was generally used in ancient times to produce usable quantities of iron and consumed more charcoal, ore and labour.

This device produces a blast of air with each stroke of the bow regardless of whether it is pushed or pulled. The bow makes it possible to operate the blower without using a complicated belt and wheel assembly used in traditional forge blowers. There is a brief pause at the end of each stroke where the fan stops to rotate in the other direction, but this is effectively no different to the intermittent blast of a double acting bellows of Europe or box bellows of Asia. The materials used (wood, bark, bark fibre and clay) are readily available on most continents.  No leather, valves or precisely fitted piston gaskets are required as with other types of bellows. The cords for this device wear out often so a number of back up cords should be kept handy for quick replacement. In summary, this is an easy to make device that solves the problem of supplying forced combustion air required for high temperature furnaces and forges.

 

 

Grass Hut

 

I built this grass hut up on a ridge. It’s roughly parallel with the tiled hut and wattle and daub hut that are a couple of hundred meters away down in a valley. I built it on a ridge to get away from mosquitoes in wet weather. This project took 7 days to make. I looked for a spot and cleared it on the first day, built the frame on the second, and spent the next 5 collecting grass. Grass is difficult to collect in this dry forest and I had to climb further into the mountain to get it.
The design is a simple pointed dome that’s easy to build. The tools used were simply sharp stones and a digging stick. It’s 2.5 m wide and 2 m tall. 8 lawyer cane strips were driven into the ground to form the ribs of the structure and hoops of cane were put over this to attach the grass to. Vine was used to tie the frame together and to tie handfuls of long grass to it. When the hut was almost finished a cap was made and lifted onto the top of the dome to finish it.
This hut is easy to build and houses a large volume. The shape is wind resistant and strong for it’s materials. Gaps can be seen in the thatch but not if viewing from directly underneath meaning that it should shed rain well. A fire should be possible in the hut as long as it’s small and kept in a pit in the center.The reason the hut took so long is due to the scarcity of grass on the hill. It could be built much quicker in a field.

Sweet potato patch

I built a fenced enclosure and cultivated sweet potatoes (from civilisation) and yams (from the wild) in it. I originally had a small 3X3 m garden behind the wattle and daub hut that already had some sweet potato and yam vines growing in it that were planted after the hut was built. But wallabies kept eating the leaves. So I made a wattle enclosure around it to keep them out.  Wood ash was added to the soil to provide potassium and phosphorus for the growing tubers.

The previous small garden was organised in rows (not seen in this video) but this was hard to water during dry weather. So I re-organised the patch into 1 meter wide mounds with pits in the centre. Vines were planted into the mounds and water poured into the centre of each mound watered the vines. So then I had a small garden with 9 mounds contained within it. I decided to enlarge the patch to fit in more mounds so I took out 2 sides of the fence and extended them by a meter each. So the patch ended up being 4X4m and contained 16 mounds. In addition to wood ash, leaf mould was added to the mounds for fertility and to reduce loss of moisture.

The patch, being in the dark forest understory, received only about 2-3 hours of direct sunlight per day so the yield was disappointingly small. Nevertheless, the patch produced a few small sweet potatoes and a single larger yam. I also picked some green growing tips of the sweet potato vine that can also be eaten. I boiled the greens slightly in a pot with a hot stone and ate the leaves. I then roasted the sweet potatoes and yam in the coals of the fire. The sweet potatoes (purple fleshed tuber) taste sweet and starchy whereas the yam (white fleshed tuber) tastes similar to an ordinary potato. After eating, I took the wood ash from the fire and poured it back into the mounds that were harvested, replanted them and watered them. In future I’d plant the sweet potatoes in an area that receives much more sunlight in order to dramatically increase production. I’ve grown the same variety at home and it produces a much greater quantity and size of tubers in full sun. Wood ash also tends to increase tuber yield and so is a good use for waste ash.

The sweet potato is a remarkable plant. It’s a staple food of many traditional cultures. NASA has considered it a potential crop to be grown on spaceships for long term missions. In terms of energy production it’s only 3rd behind sugar cane and cassava. It produces the most food value (a combination of edible energy and nutrition) of any crop per unit space and time. A study of Fijian farms using manual labour showed that ratio of energy put into farming vs yield of energy was 1:17 for rice and 1:60 for sweet potato.  It grows on marginal soil and doesn’t require much nitrogen to grow. It takes a relatively short growth period of 3-4 months to yield. All parts of the plant can be eaten including the leaves which provide additional protein and nutrients.  I grow the purple variety (because it tastes better in my opinion) but all varieties are nutritious and will stave off malnutrition. A person could potentially be nearly self-sufficient from a small plot of sweet potatoes. Note that in colder climates, regular potatoes could be grown instead of sweet potatoes.