Introducing POTBOT irrigation – no it is not the name given to a tubby robot that does the mundane and time consuming task of watering. POTBOT is short for Plant Pot – Bottle dripper Irrigation. Batches of water are trickle released from the main water tank (for security) to batch storage then electronically released to fill in effect little water tanks all set at the same elevation around the garden. These pots drain out to each bottle that is charged and topped up to slowly release the water over several hours by transfer through soil inside the bottle. The moisture passes through the soil, through the holes in the underside of the bottle and out through the soil in the garden bed. The small vent hole squirts when the bottle is full so it is easy to check what might need unblocking soon after the pots are full. By the way, I did a search for “tubby robots” for a laugh and found this amazing Australian character that might be hired to “push some permaculture” and explain how easy it is to water your garden without feeling like a robot. https://www.tubbytherobot.com.au/
Sometimes there is no rule book and you don’t know where you are going to end up doing permaculture research. We think we have made some interesting discoveries along the way we would like to share with you. Who would have thought there were a number of permaculture modes to the operation of a water tank !
Situation – Community Garden next to a house with a donated water tank in a government housing area with considerable hardship and large numbers of unsupervised children. The site is in the bottom of a large stormwater drain and all the topsoil had to be imported and inset into the cracked clay base full of old gum tree roots.
Challenge – Anything planted in the garden would die quickly unless it was watered regularly and sometimes twice a day. How do we distribute the tank water efficiently, conserve as much water as we can automatically, not lose it to the dry cracking clay below. We had to do all this with minimal cost components least likely to be stolen or result in high amounts or complicated maintenance? We have rain around here that falls out of the clouds every few weeks but the air is so dry that sometimes only very small amounts hit the ground. How could we amplify the fresh rain getting to plants? It also had to not create mosquito habitat if possible.
I read up and watched as much as I could from this permaculture website and there are some great examples but they did not quite fit our situation. It sounds almost impossible and at times we felt pretty stumped however I kept reminding myself of the permaculture principle “Within the problem there is the solution” and ended up with solutions so much better than I imagined initially. This also lead to some bonuses we had not even considered.
1. Problem :- We had to connect the house down pipe to the water tank quite a distance away.
Solution :- Using one large diameter 90mm stormwater pipe, if we ran this up to the top of the water tank, provided we also connected the bottom of the water tank back across through a valve to this large pipe, it could be used to deliver water back half way along the property in taps off this single pipe.
Bonus :- If the valve on the outlet of the tank was turned off then fresh rain could be stored separately or delivered direct to the garden beds to amplify the rain getting to garden beds even during light sun showers. Fresh rain is more beneficial to plants than old rain because of the nitrogen and dust content. Placing a water level pressure sensor in the downpipe is not essential but useful in research to check for leaks and remotely monitor the water level in the water tank if the valve was left slightly open. We can also see the rate at which water in the batch dose tank is used and the shape of flows coming in from any rain events.
2. Problem :- Cracked clay under the garden beds was drawing away moisture from the vegetables and the sun was literally baking some of the tomatoes on the bushes. Hot and dry bush fire conditions meant watering was needed twice a day some days and this could take hours.
Solution :- Polyethylene sheet was laid over the clay and covered with topsoil. Under the poly sheet we buried weeds we did not want to see again. We walled up the sides of the garden bed with the poly sheet to make wicking beds to aid watering from underneath. A ball valve setup with a toilet cistern was used to try and maintain a water level in the garden beds but it blocked with the high nutrients and dust in the rainwater and leaked due to lack of pressure. Unfortunately this water logged the plants when it leaked or if there was heavy rain. The corners had to be folded in and down to allow leaching of any excess water. Wick watering from below was no longer possible and drippers from above would also block. We also discovered gum nuts coming through the pipes sometimes that blocked even 13mm tubes. For a while there we thought we had more problems than solutions. That is when I realised we needed to take advantage of the low pressure and slow down the delivery so the plants could also take advantage of the situation. We did not need high volume and high pressure if the restriction on outlet flow was back at the water tank and this charged an appropriate small batch dosing tank and the storage volume in the downpipes. This meant that if there was vandalism or a tap opened up and left on, it would give the impression the whole tank would drain but it would only drain the batch tank and the downpipe and show the loss of water up on the water level sensor. A trickle out of the water tank would be lost until the leaking tap or vandalism was fixed.
3. Problem :- There were no volunteers wanting to water the garden or just even turn on a mechanical timer daily. There were also potential security problems in the area.
Solution :- Utilise an electronic ex-smoke detector battery controlled solenoid valve that could be opened automatically at set time intervals and for set durations. Some adjustment would be needed occasionally to deal with weather and tank water level changes but it would take hardly any time. Occasionally the irrigation system would need checking to see it was not blocked but this was easy to check and easy to unblock.
4. Problem :- How to attain relatively even distribution across all the garden beds and deal with varying water pressure head in the water tank? 19mm diameter poly pipes were needed off the 90mm PVC stormwater pipe or friction would hold back the flow too much and potentially block too easily.
Solution :- Utilise very slow release from the water tank into a batch tank then electronically controlled release to interconnected mini-tanks that were in fact cheap plastic outdoor flower pots used to accumulate and accept an appropriate proportion of each batch and then slowly release this out in 8mm micro tubes to each dripper.
Bonus :- not burying the microtubes at the garden bed meant their position could be adjusted and they could be easily unblocked. Burying the 19mm diameter pipes to interconnect the flower pots from below meant that any not being utilised would in turn direct their water to the other pots.
5. Problem :- Some of the bottles closer to the pot might get more water than others further away due to pipe friction.
Solution :- Microtube is the cheapest pipe at about $35 per 100 metres so making all tubes are the same length and just coiled up results in the same friction and so evens out distribution. Alternatively bottles closer to the pot could have their micro tube inlets bent up inside the pot so they stopped irrigating earlier and the other more distant bottles ended up with the same amount of water but over a longer period.
6. Problem :- How do we design a dripper that does not block, stores water for even slower release at the plants and does not cost anything, minimises loss to evapouration and is easy to check and adjust?
Solution :- Using PVC fruit juice bottles with flat sides, about ten 2mm holes were poked in the side of the bottle laying down and a hand full of clay thrown into the plastic bottle. An 8mm hole was drilled in the lid of the bottle for the micro-tube to insert from the header pot supplying the 4 bottle drippers needed on each garden bed. The clay sealed the holes so well that water would not flow into the bottle so a 2mm air vent hole was poked in the top. These bottles sometimes took about 6-8 hours to drain dry depending on the type of soil in the bottle. The bottle laying on the soil of the garden bed has its moisture drawn out by the soil either side of the holes in the bottle. When the bottle eventually fills with water then a small fountain of water pops up through the air vent. Sometimes it blocked but unblocked when the water level subsided. Sometimes the 8mm micro-tube might block back at the header pot but this was easily back flushed with a squirter bottle. The blockage was mainly caused by throwing topsoil in to try and seal some of the leaks in the bottom of the pot that were not properly sized. Unfortunately the topsoil had sawdust mixed with it but it did not cause too much of a problem.
Bonus :- The plants had access to moisture for longer and it fanned out in a 600mm radius after hitting the plastic liner below. It was good to not have over saturation and minimise time when moisture in the soil dropped too much.
7. Problem :- How do we measure how much water we have on the other side of the fence inside an enormous water tank? Another water level probe was not the answer because the data only came through once a day and we already had a glimpse of the tank water level from inside the down pipe when the valve in the bottom of the tank was open. The readings were only taken every 10 minutes and reported on over the internet every 24 hours. What we wanted was a way of seeing the water level in the downpipes as well. The option of installing clear sight tubes was obvious but this would have grown algae on the inside and the clear PVC would also have gone white due to the damage by sunlight. It would also have been open to vandalism.
Solution :- The solution was to install a pit under the ground and coil up the two clear plastic tubes that had vent valves on the end to allow air in once they were hung up on the fence. The water level in the tank and the downpipe/batch tank could easily be seen when timing how long it took to fill the pots and set the electronic valve to close. This was going to need adjusting occasionally as the level in the water tank went down. Once the readings and timing was done then the valves on the tops of the clear tubes were closed to stop the water leaking out and they were coiled up and locked away in the pit under ground – safe from the algae, UV and vandals.
It is not ideal using so much plastic in this irrigation system but I can not see any other way of achieving this level of water conservation, benefit to plants, balanced delivery, low maintenance and cost savings. These are food grade plastics but how they behave in the sun and under the influence of organic acids and micriobiological interaction over a protracted period is unknown. It is possible that the bottles might be able to be buried out of the way of the sun and UV damage once we learn enough about clogging and any adjustments that might be needed. Little snorkles would be needed on the air vent in the top of the bottle that would also fountain when full. We certainly get some interesting algae and slime growing in the bottles with the warmth on the surface and this probably adds to the nutrients and diversity of soil ecosystem. The little green house effect in the bottle warming the water prior to irrigation might also be important. There might be better types of plastic that become available eventually. It was the ceramic pourous watering pots that gave me some of the idea initially as well as the drought watering done with inverted plastic bottles in the garden. This system keeps topping them up with water as required.
This is system is designed to enable a single x-smoke detector battery powered automated watering valve to deliver even distribution by gravity using low cost components and adjustable to deal with with gradual variations in water tank head pressure.
Modes of Operation
There are several manually adjusted modes to the PotBot Watering System
1. No Rain Mode – for rationing water release from the water tank and at a slow rate to minimise risk of accidental release of whole tank.
2. Light Fresh Rain Amplification Mode – Holding back old rain in the main water tank and running the fresh rain direct to plants because it has dissolved gases and nutrients in it they thrive on.
3. Light Fresh Rain Storage Mode – Holding back old rain in the main water tank, filling the batch tank and down pipes with fresh rain if enough rain is falling directly on the plants. Any excess goes up into main tank. The best rain for plants is fresh rain because it has dissolved gases and nutrients in it they thrive on. In this mode old tank water is kept back in the main tank in anticipation of rain so fresh rain can be stored separately and only released if not enough rain directly falls on the plants. When the garden beds eventually need watering again the stored fresh rain is ready to be used first and at bigger intervals and potentially less volume than when drier.
4. Heavy Rain Storage Mode – Everything is turned off so there is not leakage and maximum storage.
Generally this 4 stage cycle starts again when watering has to recommence and fine tuned with valves A. D. and E. depending on the tank water level and amount of watering needed. Sometimes light rain might cause reversion from Mode 2 or 3 direct back to Mode 1 without much change to main storage.
1. No Rain Mode Settings: Valve A is set to trickle out enough water from the main old water tank so slowly that there is enough water when the electronic valve E opens at a pre-set time for a pre-set duration and letting through water at a rate determined by preset valve D. to fill all the pots and bottles with the water from the batch dose tank. Sight tubes with Valves C and B are turned off most of the time and coiled up in a pit in the ground but only turned on when hung on the fence to see the water level in the main tank B. and the water level in the batch dose tanks and the down pipes all of which are on the other side of the fence.
2. Light Fresh Rain Amplification Mode Settings – In expectation of fresh rain, turn off valve A and after scheduled use of the batch tank, turn open Valve D and E. Set Valve D with restriction enough not to overfill the pits in a rain surge and just back this up into batch storage or even up into the main tank. If enough rain for the plants is going to fall directly on the plants then set to Mode 3.
3. Light Fresh Rain Storage Mode Settings – In expectation of fresh rain, turn off valve A and after use of the batch tank, turn off Valve D to save as much fresh rain as possible in the batch tank. If enough rain falls on the plants then hold back the batch tank fresh water until needed but if not enough has fallen on the plants then open D and E and water enough to make best use of the fresh rain from the batch tank fresh off the roof.
4. Heavy Rain Mode Settings – Close all valves to maximise storage in the main tank. When more watering a few days later then reset D. and E. to deliver just enough batch tank water that is fresher than the main tank water and then when it needs replenishing open valve A a little and adjust D. and E. again for the higher pressures.
The plants seem to thrive and that has been without really fine tuning the system and trying all the different soil and hole combinations. It seems to be like a combination of wicking beds and drip irrigation but using less materials. The moisture spreads out and then rebounds from below off the liner. I am now considering how this concept might be used to apply greywater (not with open pots) and with careful consideration given to odour control. The soil in the bottles might gum up with greywater contaminants such as hair, skin fats and oils and have to be discarded every now and again if they don’t compost down in the bottles quickly enough.
This process might also be used to efficiently to water the vines that are the basis for Lumbuck Thornton’s Agloo designs that are new types of human habitation consisting of a room that is moved in and out of a shade tunnel and back into a weather proof core. These look like a vegetation based igloo facing the sun. Multi-storey versions of these might spring up to create new types of low cost and low impact cities where rooms moved on tracks laid through in scaffolding covered in and eventually supported and strengthened by giant vines of food.
This is still research in progress and hopefully others will comment through this website on their experiences and we can refine things further to find out what works best in the bottles and all the other adjustments that can be made. It could also be used for watering trees and I like how it gives you more time to wonder around your garden and observe and pull weeds and pick crop etc when all the watering is happening.
A powerpoint animation showing visually how this whole system works for educational purposes is under production and should be available in a month or so.
The permaculturenews.org website was central to sourcing some ideas and inspiration from others around the world, the social media website Yammer assisted our gardening community with sharing of ideas and communicating locally. Waminda Community House provided valuable coordination and administrative support and funding was via a small grant from the State Government of Victoria Australia. I would also like to thank the Jazzaratta Big Band and Rose City Band for their musical therapeutic, creative and celebratory fun contribution that helped to facilitate this really positive ground work. Music so often does not get the credit it should. Henk from Shepelec supplied the internet connected computer probe that enables remote monitoring and Philip Handcock the plumber in Benalla both helped me crack some of the technical problems. My family let me experiement with this community garden first and one day I will try and do more with the garden at home. The Benalla Sustainable Future Group also played a part in motivating this work. Benalla Rural City Council also assisted with the donated water tank delivery. A Department of Justice corrections gang greatly assisted with digging trenches and cleaning up the garden recently.
– These articles contain research ideas and our local experience. Note that your circumstances, site risks, local public health issues with water quality and mosquito control issues may be very different. Check with local authorities if you are unsure and make the appropriate adjustments or take appropriate precautions to protect yourself and others from these local risks.