A guide to polytunnel irrigation

A guide to polytunnel irrigation

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 polytunnel

Uneven 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 polytunnel

Setting 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 timer

A 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.