Catching Polytunnel Rainfall

We’re on metered water at home. That means that water = cash outlay. Every drop of free (and better quality for crops) rainwater therefore becomes useful. Sheds and greenhouses can be guttered either conventionally or with a bit on inventiveness. Polytunnels can be a bit more tricky. There are YouTube vids which are really good on the subject but can involve a fair bit of engineering and outlay. I’ve tried what I think is the easiest and cheapest.
Tile edging.
It’s got to be CURVED edging and the drainage capacity is limited but if stuck with its own adhesive backing or with double-sided exterior tape to the sides of the polytunnel and aimed into containers, it can harvest 40-60% of normal rainfall and 100% of light showers. It won’t catch all of a real downpour.
In the UK, Screwfix edging costs £3.99 for 3m. Got to be worth a try? + some double-sided tape.
In a dry period, it’s a good time to think of getting the rain harvest planned - for when it inevitably comes.


We’re with you on collecting rain water! We have well water but found a food grade water tote and are planning on connecting it into our house downspout and then running a hose into the garden, why waste a perfectly good gift! We always noticed how much better the garden grows after a good rain.

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Angela, you raised a really important point. The house itself is the best source of rainwater if you get downspout connector kit(s)and divert it. With the vagaries of climate change, it is truly worth maximising the chlorine-free gift that eventually has to drop and the home building receives the major load. It means a little bit of capital outlay but in a couple of years it will repay you handsomely, especially if you pay your water bill as by the meter. It is also eco-positive whether or not. Thanks, Angela for bringing that into focus.


The adhesive tape idea is fine until you get a good, solid downpour and then the guttering becomes very heavy, it comes away and can tear your cover. The solution may be to bang in short wooden posts right next to your tunnel, fix your guttering to that and use the adhesive tape to fix a length of poly sheet from the tunnel to the guttering to direct the water flow into the gutters. This way you can adjust the heights of your posts to get a good flow into your storage butt. And you’ll always need more storage than you think…
Using posts, the weight of the water is not on the polytunnel cover and there is little or no risk of stretching or tearing the cover. You could use 10cm (4 inch) treated posts from the garden centre (my Dad used to call them tomato stakes but I reckon it would be a pretty feral tomato plant that needed a stake that solid), screw the guttering clamp onto the top or outside of the post or screw the guttering onto the posts and cover the screw with a big gob of silicone to seal leaks.
It is an outlay of money but if it saves you several cubic metres of bought water a year for several years then it may be worth the outlay. Especially if our weather is going to get hotter and drier over our growing season.

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Sounds like a good system, Alli, but I don’t think you quite got the gist of my suggestion. The tile edging only weighs a few ounces, is flexible, and even in a downpour will only contain less than 1/2 pint of water over its entire 3m length. Your system is better but more sophisticated and expensive, well suited to larger allotment-sized tunnels. Many small garden tunnels will have stretched in the winds and need a flexible system. I guess it’s a matter of horses for courses.

No, sorry, I did presume you had a bigger tunnel. If your guttering holds less than half a kilo then adhesive tape should be fine. I hope you’re not in a place where lockdown prevents you from being able to buy the necessary items and that you can get it done during the Spring rains!

OOh! Have a screw fix card, what a good idea…

Spring rains! What Spring rains? We’re gasping for some decent rain in the UK Midlands. Sounds weird after being drenched for two months in Feb-Mar.

Let’s hope you see some soon. It looks promising for next week.

@laner8673 I hope you’ve been getting some rain this week. It’s been torrential here.

Hi there AlliG - We’ve definitely had some rain (including heavy and some sleet) and rain on-and-off was predicted for the following week. Suddenly, it’s all change and two more dry weeks are predicted. I’ll have to get the rest of the 2nd shed guttering done as I missed a lot of the previous. Hope you’re OK