Planning your first polytunnel (Wales)

Good morning from the temperate North Atlantic climate region .. I hope all is well with you & yours.

May I seek the wisdom of successful polytunnel growers, especially those of you with similar climate to ours?

Our weather is not as temperate as it was 50 years ago - we're getting more, and more intense storms, as well as more and more intense heatwaves (up to 40 deg C for the first time in 2022).

A dear friend in Wales who, like me is Disabled, wants to carry on being able to grow food in their fair-size sloping garden.

What would you advise as the process for deciding what proportion of the garden to devote to a polytunnel?

The polytunnel needs to be large enough to walk into, and ideally, able to be converted to wheelchair access in due course.

What size is good for one person to maintain?  What types and manufacturers?

I have some initial thoughts from my experience helping with polytunnel growing and siting, which I'll put in the first reply ..

Many thanks!

1) Orientation - how best to orient the tunnel frame & doors relative to the worst (not necessarily prevailing) storm winds?

2) Watering - some kind of gravity-fed rainwater system, using the existing slow, could make the tunnel a lot more productive;

3) Ventilation - passive through ventilation system to help keep polytunnel plants alive in increasing heatwaves;

4) Visiting animals - helping them leave as well as they might arrive, and having more of a thriving ecosystem to help reduce trapping of all kinds of animals.

5) Affordability vs. practicality - although secondhand is more affordable, new-buy will probably be less demanding to get set up.

6) .. your thoughts here .. !

Many thanks!

First off - is a polytunnel right for your friend? There are ups and downs.
On the positive: obviously creating a warmer, sheltered microclimate; indoor gardening for a wet climate is lovely!
On the negative: the short life expectancy of the polythene cover - you need to balance resources used with resources gained (fresh, local, nutritious food, fresh air and excercise in all weathers,...)
If they are experiencing warmer summers and more severe storms, maybe a tunnel is not the best option? polycrubs have become quite popular in the Hebrides due to their apparent greater durability, and greenhouses can often be had secondhand for little money or free. Maybe this thread about aging on a homestead may give some other pointers about making gardening easier with increasing disability.

You say the garden is sloped - that immediately makes it a bit more complicated, since most (?all) tunnel manufacturers advise placing the tunnel on a flat area. Having had one tunnel oriented up and down the slope, and my new one to be stepped side to side, I know that this isn't strictly necessary, but will make fitting the cover more complex - It is difficult to get a nice tension on the cover especially if sloping along the length.

polytunnel on slope up-down

new polytunnel on steep slope side-side

I could see advantages in both orientations depending on the access that your friend has. If the tunnel is oriented up/down the slope it is possible to create a through draft from the thermal effect of the heat rising. However many manufacturers these days can include a waist level bar that the cover fixes to, with moveable ventilation panels below that. Together with a high level vent in the ends above the door a good amount of ventilation can be achieved in hot weather.
My inclination would be to orient the tunnel across the slope – With a raised bed either side, a small tunnel might even be made using plastic water pipes with some wooden bracing.
It occurs to me that a geodesic dome built on a slope might give an interesting keyhole bed effect that may work well as raised beds.

raised beds in dome greenhouse

image source

The main thing that is unusual for most of us in the UK to deal with, is the need to water the plants - It doesn't rain in the polytunnel. This may seem obvious, but does mean that watering the plants becomes a real and necessary task, depending on the plants, their ages and the soil etc. More so because the hotter temperatures mean that the soil dries out and the plants become thirstier than they would outside. Luckily there are various ways of dealing with that. A polytunnel waist level bar could carry guttering to collect rainwater. I’m hoping to collect rainwater in this way on the up hill (and prevailing wind direction) side of my new polytunnel. The water can be stored inside the polytunnel where it will also act as a thermal store and humidity contributor to aid against spidermites.
You could also consider wicking beds enabling less frequent watering. There's a thread about a wicking bed set up in Wales: Dave's self watering greenhouse

Many thanks!  I'm sharing your thoughts with my friend, although I fear geodesic domes and polycrubs may be beyond their current budget, sadly.  

I had a little look at dome construction when I was building my yurt-shed, and some of the constructions using hoops looked like you might be able to make them fairly economically with hoops of plastic water pipe for example see my post with some links.

I did a quick sketch of how a simple polytunnel with raised beds may work on a side slope:

polytunnel with raised beds

Again, this might be done with plastic hoops, like a larger version of a cloche.

Hello Ac,

Is the polytunnel project for your friend going well?

We moved to a property in the North of Scotland that came with a large polytunnel. 3.5 meter by 9 meter? Something like that.
I tried to make it work for 5 years without great pleasure or succes. 2 months or so I cut the top off and so far I'm much happier with my nunnel (non-poly tunnel) than I ever was with the tunnel. My cabbages have no mildew for the first autumn ever.

Now most people seem very happy with their tunnels, so there must be something in it. For me it wasn't worth the effort of watering, airing and the continually trapped insects and animals.

The inspiration to cut it came from the Shetlandish plantie crubs, that are basically surrounding walls to keep the worst of the wind off. You can put over netting if you were so inclined. (I'll try to ad pics)
For me, some conjunction of plastic tension and gravity have allowed me to keep a poly sheet up on the wind side for now, the other side is garden netting I had. In spring I'll add another layer and grow peas and runner beans up the side.

Probably not in the same order:

For airing/positioning I would try to catch the prevailing wind on the head side so you can install 2 doors and have them open so the wind can blow through most of the time. Netting bottom sections seem to be a trend too, I'd definitely want those in a tunnel.

Watering is a major, major job. And that's when everything is working. Repairs and unforseen circumstances must be exponentially harder when disabled, so this would be a major concern for me. A passive watering system with no moving parts sounds a solution, so a seep bed would definitely be high on the list.
Gravity and tunnel placement could work really well on this if you can get a flow to/through the tunnel somehow.

Animals get trapped, even with two doors open at all times. Birds and rodents can usually figure it out, but insects just try to keep flying to the light. People tell me they'll get out at night if i don't catch-and-release, but even then I can't see how a day locked in a hot dry tunnel is good..
Opening top panels like in a geodesic dome may be a solution. Or no top

Poly tunnels are relatively expensive and the plastic will need replacing regularly. More cost and such a pain to do, even with 4 non-disabled adults. And don't forget your plastic will need cleaning. Our big tunnel was too big and even with a ladder my very tall partner couldn't reach the top outside to get it properly cleaned. And just a bit of grime throws a lot of shade
Raised cold frames may do a similar job for a fraction of the price and upkeep. If placed well and raised I can imagine these as very wheelchair friendly.

Planning your crops to suit the circumstances really helps. I got Covid at the height of the growing season a few years back and was out of gardening for nearly two months. What a mess my annual beds were. Now I grow perennials whenever I can.
We grow portuguese longer-lived kale/cabbage. I'm not sure how long they live, but even if not fully perennial they'll last a lot longer than annuals. The leaves you want to pick will grow higher, so no bending required. They didn't like the tunnel, but outside they thrive. So less planting, easy harvesting.

Our garden is shady, but my neighbour is getting elderly so he offered me use of his sunny glass house. Smallish, but walk in. So I grew 8 tomato plants in there. And sure I could have watered a bit more and gotten a better harvest, but even for a potentially double harvest of what I got, it was A LOT of watering.
Will I grow tomatoes again? Yes, because delicious. But I'll find a way to make them self-sufficient, or at least self watering.
Will I tell people to also grow tomatoes? Not without warning that it is a lot of work if you do it under cover

So, if I were you I'd start by building your friend a few big raised cold frames and a few raised beds near his house. And get a passive water source going.

I hope you do well and do send us pictures when finished!