A guide to polytunnel irrigation

Irrigation water timer

Drip irrigation in a polytunnel

This might seem an odd time of year to talk about irrigation but if you are thinking of adding a watering system to your polytunnel or greenhouse now is the time to get it done. The best solution for watering a tunnel is either a soaker hose or a dripper system which runs at soil level because there will be less water wasted through evaporation and you will reduce fungal problems on wet leaves.
Obviously soil level irrigation is much easier to install before the plants go in. Both systems are easily attached to a garden tap or hose and are simple to join together and achieve whatever configuration you may need.

drip irrigation lines in polytunnelUneven watering puts plants under stress and leads to bolting (running to seed), woody roots (beetroot) or splitting (carrots and tomatoes). If you are anything like me watering can be patchy at the best of times, especially when things get busy and you don’t have the time to do it properly. Water evaporates quickly from the soil surface, especially in hot weather, so there may be less than you think getting to you plant roots. If I was to give you one tip on polytunnel growing it is even watering, it really is the key to producing the best crops.

Here are 5 reasons to install a water timer and simple drip irrigation system:

  • It will save you time.
  • A drip system can deliver water more effectively directly to your plant’s root zone.
  • Set the timer to come on early in the morning when it is cool so water soaks into the soil rather than evaporating.
  • A drip system can deliver a more precise amount of water, and it will be more consistent than hand watering.
  • You can go on holidays!

Tomatoes growing in a polytunnelSetting up an irrigation system can seem complicated is actually very simple and easy to do once you understand it, it is really plumbing for kids. All you will need is a Stanley knife to cut the pipe, everything else just slots together and is tightened by hand. I quite enjoy working out the systems to be honest so if you need a hand let me know, I can draw you up a plan and give you a parts list for everything you need.

Basically you start from your water supply (tap or hose) end where you can add an optional timer or filter if you need one. The water is then carried to the area you want watered using a supply pipe (black, no drippers) where it connects into your irrigation pipe (brown, with drippers). You can have as many dripper lines as you wish and can send them any direction you like using the range of T pieces, connectors and elbows etc.

Drip irrigation plan for a polytunnel
The dripper pipe comes with tiny valves embedded in the tube every 30cm which irrigate at a rate of 2.3 liters an hour. If you are running up and down beds it is best to place your lines 30cm apart. If you have large (and thirsty) plants like tomatoes or cucumbers you can run a separate ring around the root area of each plant by taking a ‘T’ off the supply line and using another ‘T’ to loop around the plant as shown above.

You can further control your network by adding in line valves at each sub section which allows you to turn off areas that don’t need watering as much as the more demanding plants.

drip irrigation parts shop

If you would like to order irrigation parts I have arranged them on a single page on our website to make it easy to build a system and check the total as you go. The image above is for illustrative purposes but on the live site you can click on the blue ‘i’ buttons for any more information on any of the fittings.

Irrigation water timerA word on timers
We have had a lot of trouble with domestic water timers in the past so have decided to stock the professional units we use in ourselves. These units are obviously more expensive than their domestic cousins but they will last for years without giving you any trouble. The common problem experienced with timers is the valve unit eventually leaks into the control box and ruins the unit. The professional ‘Baccara’ units we stock are different because the control box and valve unit are separate parts and made to professional standards.

Given that an automatic system is supposed to give you peace of mind when at work or away on holiday I feel it is well worth investing in a relaiable timer. Yes, they are nearly twice the price but they will last at least 5 times longer and give you the confidence you need.

  1. Tim

    PS I should have specified that the above query is regarding the Baccara automated timer that you recommend for an irrigation system

  2. Joe Lasek


    Nice article, cheers for the info.

    I have a 100ft poly tunnel, 16ft wide with 3x 1.4m beds with a break in the middle for a seated area for winter. We have a right mixed bag in there.. Super hot chillies, aubergines toms, cucumbers, beans sweetcorn etc. Some plants are more thirty than others can we overcome this?

    what’s the deal with soaker vs dripper, there is so much conflicting info out there. Which ones best.

    I’ve heard water pressure can drop over bigger distances will this affect us in a larger poly?

    What do you reccomend? I can send pictures via email of you require.


    Joe 07939872142

    1. Andrew

      Hi Joe

      I prefer the dripper as it is easy to calculate your water usage as each dripper emits a fixed number of litres per hour, you can easily calculate the amount of water used my multiplying the number of drippers in your lines. If you have decent water pressure to begin with you should be OK in your tunnel. As regards your different plants I would install a number of circuits controlled by separate timers, it is all pretty easy to setup. I hope this helps. Andrew

  3. Derek Brooks

    Hello – about to build a polytunnel (25 feet by 12) for a school. In your experience, which is safer – drip or overhead? With the overhead, how frequent are the upright supports? I am trying to work out which system is more foolproof! Thanks.

    1. Andrew

      Hi Derek. Good question. Personally I prefer drip irrigation. It’s easier & cheaper to install. It’s more efficient than overhead too as you will waste less water. You can add a layer of mulch over the pipes to save even more water from evaporating. With overhead you run more risk of blight and other fungal diseases. Hope this helps in your decision!

  4. Polly

    Hiya, we are setting up a new polytunnel, for a community project, 20m by 9m, with 4 beds running the whole length. Roughly how much will a drip system cost please? Many thanks

  5. Dan

    Hi – I can’t find the page on your website for the drip irrigation – could you send a link please? For info I have a 30ft poly tunnel and I think I’ll need 6 runs of the dripper hose x 10 metres

    1. Andrew

      Hi Dan, unfortunately, we don’t carry irrigation equipment anymore. Hopefully this article has helped you determine what you need.

  6. Abi

    Hi, is it possible to do some kind of drip system from a water tank or will they only work from the pressure off the mains. We have access to a large pond and was wanting ideally to use water from that but it would be collected in ibc’s.

    1. Andrew

      Hi, yes, you could do that but you would need to make sure you have at least 2 bars of pressure, this will depend on the fall. If you are using pond water I would highly recommend a filter.

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