Project 9

‘Permaculturing’ the Polytunnel (2011-2013)

Summary and Lessons Learnt

This project developed from problems experienced with a conventional polytunnel set up – and has dramatically increased the efficiency, productivity and overall sustainability of our food growing system. As result of the simple changes implemented in 2012 (one of the worst years for tomatoes by all other accounts) the polytunnel produced a crop of tomatoes that we are still eating (frozen, no tins of tomatoes needed) from summer 2012 to March 2013. Further seasons will show if this was a fluke or not, but the effort and savings in terms of reduced watering in itself have been a great success.

Ethics

Earth Care – The polytunnel is part of our sustainable, low energy input food production system. It has recycled waste materials such as bottles and paving slabs, and uses renewable resources such as solar gain and captured rainwater.

People care – The whole system is providing food for the family plus extending the growing season so that I can provide winter salads and later harvests to provide more home grown, organic vegetables for the family.

Fair Share – this has been a major point of interest for people visiting my plot when I run open days. As a demonstration project in the future it will hopefully allow others to see how increasing solar gain and sustainable watering can be easily applied to their own situations and enable them to gain a yield. Surplus produce is often given away.

Criteria & Principles Demonstrated

This project has been designed with OBREDIMET and has also demonstrated the use of Observation and Evaluation skills, Incremental and Rolling design, Functions and Elements analysis. It demonstrates the following Key principles :- Catch and Store Energy, Obtain a Yield, Produce no Waste, and Integrate rather than Segregate (by integrating the house roof to the polytunnel watering system).

‘Permaculturing’ the Polytunnel

Observation& Boundaries

The Starting Point

When we moved, a prime focus for me was to have a polytunnel. Siting it was done with permaculture principles in mind, especially after hearing the story of Many Pullen’s polytunnel at Ragman’s Lane. So when I sited it I used the following criteria:-

  • Close to house as possible but away from light excluding trees including oak in garden, for ease of picking on evening route
  • East/west orientation to give hot side, cooler side for salads
  • North side of property to avoid hedges and neighbours shading in winter
  • Least windy site as possible, or at least not directly against SW wind or wind sock to it
  • Close to chicken and duck area for receiving bedding, duck water, chucking weeds/ surplus greens over to feed chickens, letting them in when cleared for pest control.

Problems/ Limiting Factors

Although the relative location has remained the most optimum I can think of, problems with the polytunnel soon started appearing.

  1. Watering

Watering with a watering can proved time consuming and ineffective quite quickly which meant I was using the hosepipe connected to mains more often than I wanted. Even this is time consuming and only seems to water the top inch of soil so I tried using a sprinkler – BIG mistake, the humidity in the tunnel increased dramatically and blight became a serious threat to all tomato production. Surface watering was not penetrating and the soil was losing moisture even under mulches of grass mowings – all dessicating to nothing very quickly.

  1. Nutrient Loss

After the first few years I noticed that crops were getting poorer growth despite the regular application of compost mulches, green mulches (mainly mowings) and use of comfrey and nettle homemade feeds. The sandiness of the soil coupled with the lack of moisture due to poor watering was drying and dissipating mulches very quickly and the soil seemed hungry. The worm situation was very poor again due to the dryness I suppose. I came to the conclusion I needed much thicker and richer mulching.

  1. Voles

After the first year or so, I noticed tunnels appearing under the soil, usually following along the plant roots. Following the tunnels I found chewed holes through the sides of the plastic! These little tunnels were voles happily munching on my peas and other produce, but worst of all causing plant wilt as roots were left suspended in vole tunnels.

  1. Frost

After a while I realized that my whole garden is sitting in a slight frost pocket caused by air flowing down from the hills surrounding our property. Although not at the lowest point in this plane we seem to be at a frost stopping point as the buildings next door seem to trap the frost. Also the trees, trellis and climbers surrounding the garden act as another frost brake I think.

List of Requirements– Addressing the above Limiting Factors

From all of the above observations, I developed the following list of requirements to address these limiting factors and improve the polytunnel:-

  1. Improve the soil nutrition, soil life and get worms interested!
  2. Protect soil from heat and water loss
  3. Get rid or at least hinder the vole tunnels
  4. Create a self-watering system which didn’t rely on my time or mains water
  5. Reduce air humidity caused by watering
  6. Extend the frost free season as much as possible

Resources

The following resources were available on site or in the local area.

  • Old paving slabs, breese blocks, recycled wooden boards
  • Wine bottles!
  • Old guttering and downpipes
  • Existing soaker hose
  • Recycled containers & existing water butts
  • Local manure & mushroom compost, urine from compost toilet, poultry bedding and dirty duck water
  • Large sheets of plastic from previous polytunnel covering, some holes

Needed – timber for posts and guttering support, guttering stops

Evaluation

The list of functions that the design had to accomplish was then easy to breakdown into systems and elements. Clearly the analysis was showing the obvious opportunity for multiple function design - raised bed edges could perform several jobs at once by increasing mulch capacity, excluding voles, and increasing solar thermal mass.

Functions / Systems / Elements
Automatic, non mains watering that reduces humidity / Rain water harvesting & ground level delivery / Buried soaker hose
Large capacity water storage
House water diverters
Delivery Hose to/from storage containers
Polytunnel roof collection system
Frost Protection / Solar thermal gain system
Planting barrier / Increasedmass around beds
Reduce heat loss somehow?
Increase tree/fenceline planting along north/east edge of property
Vole Barrier / Barrier mechanism / Buried barrier at edges of polytunnel
Soil Improvement / Better recycling nutrients within larger system
Barrier to heat and water loss / Raised beds, Source rich source of compost
Recycled duck water
Poultry manure & bedding, human urine

Design and Implementation

The design for ‘permaculturing’ the polytunnel evolved in response to problems over several years. The first design was purely to capture water from the ‘roof’ of the polytunnel after several retailers told me it was not possible to do this.

First Polytunnel Self Watering System Design (2005)

An initial early on design had been to capture rainwater from the polytunnel roof and direct it immediately into the tunnel. The rainwater was collected by means of a strip of plastic sheeting taped (greenhouse water resistant tape) to the sides of the polytunnel. The strip then sat in a free standing guttering angled to deliver water to four waterbutts standing at the corners of the polytunnel. This is another reason I sited the polytunnel within a ‘furrow’ section to enable water from these butts to be delivered to the slightly lower beds within the polytunnel. This design was implemented early soon after the polytunnel had been built in 2005.

Problems with this design however soon became obvious.

  • The tape broke down every year and needed to be replaced due to sunlight and the wind. It also left a glue residue on the plastic, which became dirty and meant you couldn’t re-stick on it very well.
  • Insufficient height to pressurise a dripper hose – the water butts were just off ground level which was ok for can dipping but too low pressure to use a dripper hose which clogged up very quickly.
  • The guttering distorted and twisted in the sun causing water to spill

Improved Polytunnel Self -Watering System Design (2012)

In 2012 we had to replace the old plastic covering that had been on the tunnel for 7 years and this made me start thinking about a new system for capturing the water on the roof and delivering it directly into the tunnel. The new plastic was more insulating but could I also increase the heat loss without damaging the sunlight by covering this again with the old plastic and using this to catch the rain on? This would give a sturdier structure and very much improve water capture, but could it also provide an extra insulation layer, though in low winter sunlight the south side of the tunnel would still be open to full light at ground level where winter salads would be. Maybe in summer when the tunnel can get too hot, the extra plastic will keep things cooler?

My main concerns are algae greening in between the two layers and wind lifting the whole thing out of the ground – NOTE June 2012 - 4 months and several storms later, not yet happened.

Water being captured very quickly with improved design – soaker hose seems to be leaking slowly from this height of water, but often problems occur later on if the hose ever dries out.

House Rainwater Harvesting and Delivery Design

To increase the amount of rain water I can use in the polytunnel and for watering of chickens and ducks (especially the refilling of the duck pond), and avoid all mains water use if possible, I quickly realized I needed to save as much water as I could from the house roof as well.

An initial design used a solar pump to move water captured from the roof of the house and stored in two 1000 litre containers to a third container that was raised 3 feet off the ground close to the polytunnel.

This was then attached to the soaker hose.

However again problems soon developed: –

  • The solar PV proved insufficiently powerful and we ended up having to attach the pump to the mains electricity.
  • The diverters were normal water but diverters and they were not collecting much water when it rained heavily so the tanks never filled up in heavy rainstorms. They also clogged up very quickly with debris.
  • Too much effort was involved in remembering to pump the tanks so I ended up using the mains tap still.

Final Integrated PolytunnelSelf Watering System Design 2012

To increase the water capture rate during summer downpours,we needed diverters that would not be overwhelmed and divert water down the drainpipe.

Also, I realized that if we delivered the water using gravity rather than pumping I could deliver it to half way up the vegetable area, providing we attached the diverters as high as possible on the down pipes so that sufficient head of water can gather to generate sufficient pressure to move the water quickly.I also increased the bore of the delivery pipe from a normal hose to a 2.0cm blue water pipe so a greater volume of water could be moved, and this is also less likely to freeze or split than hosepipe. Some interesting steeping down was needed from the German diverter to anything hose-like in the UK, which I managed with waste pipe connectors!

Using step ladders and filled water hoses we managed to find the furthest point in the garden we could deliver water at a fast rate of flow and marked it. I wanted to move the water tanks as far up the garden as possible to take advantage of the natural slop upwards, which could add pressure when delivering into the polytunnel watering system.

This optimum delivery point just happened to coincide with being close to the neighbours stable block which made me think I should also capture and store from their roof aswell. Currently I only have a normal water butt diverter attached to the tanks at this point but I am hoping to get permission to increase the capacity with a Giant Diverter if necessary – ie if I am not regularly filling tanks from the house roof and I need more water.

To allow greatest flexibility and maximize soil moisture for plants with different root depths I have kept the original soaker hose, now buried about 10 cm below soil level, which the 1000 litre tanks usually connect to. The polytunnel collecting butts are attached to the newer therefore higher system which is now under another 10 cm of mulch, therefore watering at top level. These systems could be interchangeable and indeed I may find the lower pressure polytunnel butts work better on the deeper system.

The house roof has two more downpipes which are not connected to this polytunnel system.

One feeds directly into the greenhouse, the other which takes approximately quarter of the house roof water is currently under-utilised with a normal diverter feeding to a patio 300 litre water butt. The garage roof is likewise used. There is therefore capacity to extend the system greatly and if over the next few years I find I need to store more as I’m using mains water regularly, especially in hot summers, then I will increase the capacity. This will probably require an additional 2cm bore blue pipe however, plus extra 1000 litre tanks, giant diverters and attachments so has quite an additional cost involved – so I’ll wait and see first!

Raised Bed/Solar Thermal Mass Design

Clearly raising the beds over the sandy soil, above ground level would help in improving soil quality, water retention and keeping the voles out but the brainwave was to recognize I could add a lot of solar gain by choosing the right materials.

Slabs

The decision to use slabs at the polytunnel perimeter was obvious – I had lots on hand and I could bury them upright – but to maximize solar gain I placed the taller ones on the north side, and the smaller on the south.The south ones therefore don’t cast a long shadow over the beds but they do act as radiators absorbing heat through the plastic. When I replaced the water collection system with a double layer of plastic I raised the catchment height a little (even though this might mean less water) so that when the sun is low in the winter the rays will enter through the single layer of plastic, and having the low slabs on this side does not inhibit the sun. Hopefully though any rising heat will be slightly insulated by the double plastic layer overhead.

The bigger north side slabs will also act again as radiators, collecting sun rays from low winter sun but also reflecting the light back into the beds, and they might go some way to insulating from heat loss from the soil and air on this shady side.

Voles seemed to dig just under the surface so I am hoping that the 8 inch depth that I have buried the slabs will be sufficient. (August 2012 – no holes yet!)

Bottles

I also decided to keep the original ‘bendy’ internal bed shape by using bottles – an old permaculture classic now – but what if I filled them with water to increase the thermal gain? Would they shatter in winter? A trial over winter showed that bottles with water were much warmer on cool evening than those without – and if filled 2/3rds full they would not shatter at -10 degrees. Full ones did however. A happy time was spent over the winter collecting bottles from friends and the local pub! Over 200 were malleted into the ground, a big job but very satisfying to behold!

December 2011 April 2012

Other ‘Permaculturing’ additions to the polytunnel system