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).
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
‘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.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
2. 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.
3. 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.
4. 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.
2.
3.
4.
5.
6.
Improve the soil nutrition, soil life and get worms interested!
Protect soil from heat and water loss
Get rid or at least hinder the vole tunnels
Create a self-watering system which didn’t rely on my time or mains water
Reduce air humidity caused by watering
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
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
 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
Increased mass around beds
Reduce heat loss somehow?
Vole Barrier
Soil Improvement
Planting barrier
Barrier mechanism
Better recycling nutrients within
larger system
Barrier to heat and water loss
Increase tree/fenceline planting
along north/east edge of property
Buried barrier at edges of
polytunnel
Raised beds, Source rich source of
compost
Recycled duck water
Poultry manure & bedding, human
urine
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
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 water butts 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.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
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)
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
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.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
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.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
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 Polytunnel Self 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.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
The largest capacity diverters I could find were
from Germany and called Giant Rainwater Diverter
on the internet. They are supposed to be able to
divert 90% of all rain and have a self cleaning
stainless steel mesh that directs debris down the
downpipe rather than the collecting pipe.
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.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
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 as well.
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!
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
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.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
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
Bottle edging filled
with water gets
quite warm on
sunny winter days –
overwintering broad
beans and salad and
early peas do seem
to have done better
this year with less
signs of frost
damage on beans
than previous
winter. Fig still
frosted tips in April
however.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
Other ‘Permaculturing’ additions to the polytunnel system
Permanent fencing/trellis made from
odds and sods begged borrowed and
found, to increase useable vertical
growing space.
‘Hanging’ gardens – hanging
guttering from roof bars to give
mouse free pea germination
space, using old bread trays for
extra and moveable temporary
growing space. Here very early
strawberries.
All planting is planted through previous
plant debris which is cut and left on the
surface. Fine seed such as salad is grown
by spreading fine compost on top of
rough mulch and sowing into this.
Nov – broad beans planted through cut
tomatoes,
May/June – broad beans cut , tomatoes,
chillis,cucumbers planted through
July/August – tomato prunnings left on
surface for extra moisture protection
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
Old thread spools picked up free from a
visit to a woollen mill make a handy feed
delivery method to individual tomato
plants reducing surface watering and
therefore humidity.
Maintenance/Monitoring
Maintenance of the watering system is ongoing and requires the following: Cleaning of house guttering and diverters to remove debris to ensure maximum
throughput of water ( every 6 months)
 Adaptors need replacing now and again, taps on IBC tanks are prone to breaking – so far
not replaced any parts but ‘turn off’ by lifting hose ends up above water line when not
in use.
 Soaker hose – ok when kept damp, seems to dry up when empty of water and need to
poke small holes around plant roots when replanting in the spring. Might need extra
pressure to work better, see below.
 Additional water capture plastic covering on polytunnel will need replacing after several
years I would imagine – this can be recycled/reused for cloches, extra insulation over
seed trays etc, and every time replace full polytunnel plastic (costs£100 every 7 or 8
years) we can use this for the rain capture sheet as this can have holes, etc. I should
imagine though the new covering will last longer with the added protection of the rain
capture cover.
 Bottle edging – now again needs the odd bottle to be hammered back in gain. Can
replace ad hoc.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
Evaluation & Tweaking
The evaluation of the design against my original requirements shows some
1. Improve the soil nutrition, soil life and get worms interested!
Since raising the beds and adding the soaker hose plants in 2012 have gone mad.
However I do seem to have some yellowing on tomato leaves and think it may be due to
magnesium deficiency possibly caused by too much comfrey/potassium rich plant feed in
past. Thinking of adding Epsom salts to watering system.
Soil life – under mulch the ground is damp yet no obvious signs of plentiful worms at this
level yet. Will continue to monitor.
2. Protect soil from heat and water loss
 Overwintering plants do seem to have coped better at ground level than in previous
two winters but this may be just due to warmer weather this year. More years of winter
cropping need to be observed before I can conclude. What I have noticed is that I have not
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
seen any plant wilt due or tomato splitting due to erratic watering, but then this year has
been a fairly atypical year. But all that rain we’ve had is at least getting inside the
polytunnel without my effort!
3. Get rid or at least hinder the vole tunnels
 Hurray – so far no voles !!
4. Create a self-watering system which didn’t rely on my time or mains water
 So far this summer I have not had to water by hand at all, only for giving plant feed to
tomatoes when I bail out nutrient rich duck pond. My work load in watering has
completely reduced and I have been happy to leave the polytunnel unattended to water
itself when I go on holiday so this has been easier for the neighbours!
5. Reduce air humidity caused by watering
Despite blight in potatoes outside the polytunnel, touch wood, I have not had blight
inside on the tomatoes and there does not seem to be any cucumber mildew either which
I have always suffered from before by August/September.
No sign of mildew or blight (fingers
crossed). Notice mulching with any green
material produced in tunnel, eg tomato
plant prunnings, as I am building carbon
and raising bed level by direct composting.
6. Extend the frost free season as much as possible
I still need time to assess this. I feel the stone and glass warm under touch on sunny
spring days – so this heat must be being released. I have seen and felt the soil in the raised
beds as being warmer than outside soil and have found the water in the bottles unfrozen
when it has been -5 degrees outside. All sign of success but how much is due to heat of still
composting mulch or not I don’t know.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
Further improvement s/Tweaking:The soaker hose is still operating very slowly and I occasionally poke more holes at plant root
stations when I am planting to encourage a better distribution of water. I feel the hose closes
up after a period of non-use, ie. when the butts are dry and the pressure is still fairly poor
when distributing water from the polytunnel collected rainwater which are at lower height
and size than the IBC containers.
One idea is to reuse the solar pump we had for the original system and pump water from
these collecting butts to a higher cistern raised on a platform, like pumping to a toilet cistern.
Something to think about for the future if I find that the soaker hose needs more pressure to
work efficiently.
Duck water delivery system – I am still considering how to use this nutrient rich water without
the effort it requires at the moment, whereby I fill watering cans and direct water. Usually this
is when I add comfrey/nettle juice too. Most of the time this water goes directly to the willow
patch via an old cistern and tubing, but is and when I need to get it into the polytunnel it is a
bit of a faff. It is very dirty water however and I am loath to send it down my soaker hose.
Ideas still to think about!
Winter 2012/13 – extreme gales this year broke some of the screws that fixed the wooden
batons to the planks, but luckily the plastic was not torn. For added strength extra fence posts
were added (now 6 per length) and deeper planks with bolts through the batons and planks
(instead of screws and washers) now hold the plastic sheeting in place.
.
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‘Permaculturing’ the Polytunnel Design by Alison Ensor
Things I have learnt from this project
 Water is the most important element of land base design – I knew this in theory but this
design has made me realize how precious and necessary having water in the right place
in your system is in practice. A tremendous amount of effort and energy can be spent if
the water part of your system is not in a useful place!
 It also made me realize how effective watering is so important for nutrient cycling –
dried composts are useless. Without damp soils organisms needed for the conversion of
dead matter to plant nutrient just do not operate.
 Wildlife – slugs or voles, you take your choice! On clay you get slug damage, on sand you
get voles!
 That you shouldn’t give up on a design – you can always improve on your original ideas
and eventually things begin to work!
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‘Permaculturing’ the Polytunnel Design by Alison Ensor