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There are so many positives to growing plants undercover, but one of the downsides is maintaining moisture inside your tunnel. There are many different irrigation solutions depending on technical capabilities, tunnel size and the types of crops you grow. Some people have looked further afield than overhead sprinklers or soaker hoses and are choosing to look into the past at ancient farming techniques, while others are keeping it simple and are letting gravity do its work.

Let’s have a look at the full spectrum of approaches to polytunnel irrigation, from the ordinary to the unusual.

Bottle Spikes

Perfect for containers, bottle spikes are attached to plastic water bottles that are filled, and then the spike is driven into the soil. The spigot on the side of the spike is turned to release water flow which is dripped onto the soil of the plant. These are cheap, simple and easy, but they are short term solutions. Perfect if you are frequently away from your allotment for a couple of days, or on holiday and have concerns about your container plants.

The other downside is they can be a bit of an eyesore, recycled bottles are green and ethically on point, they may suit an allotment but maybe not a well-kept garden plot.

Drip tape/soaker hose

A longer-lasting solution than bottle spikes, drip tapes and soaker hoses are perfect for inside polytunnels and vegetable plots. These can be hooked up to mains water or with a little imagination they can utilize collected rainfall water. Making less of a visual impact, these systems are designed to blend with the soil. Soaker hoses can be homemade however this also has its drawbacks. In theory, these systems are very simple, a hose that is perforated to release water where it is needed. The reality is longer hoses require something to increase the pressure along the length of the hose.

Our Drip Line Kit offers an efficient system that gets water where it is needed – at the roots. The kit also comes with pressure compensating emitters that ensures even irrigation along the lines. Some technically savvy gardeners have hooked these systems up to timers so they have complete control over their watering schedule.

Overhead system

Overhead sprinkler systems probably feel like the most natural solution to indoor watering, after all it mimics rain. Whilst overhead sprinkler systems offer a lot of positives, there are also some drawbacks. One of the less successful elements of sprinklers is the lack of control, unlike some of the other systems, you cannot be assured how much water is getting to each plant’s roots. There are also concerns with wetting plant leaves as opposed to roots as in certain crops it will make them more liable to leaf mould and blight, wet leaves coupled with the humidity inside a tunnel can cause problems.

There are upsides to overhead watering systems as well. If you are growing disease or blight-resistant crops, overhead sprinklers offer freedom thanks to timers that can be placed to ensure a thorough soaking. They are straightforward to set up and effective systems.


These are ancient methods used for maintaining moisture in beds thanks to the nature of terracotta. Ollas can be fashioned from readily available materials or made in shapes fashioned to better allow water to exude from the vessel.

Ollas work because terracotta is naturally porous. This means that as and when the soil dries, it takes the moisture from within the terracotta pot that has been buried in the bed. The downside of Ollas is they need regular refills and if you are growing something with luscious foliage, they can be hard to locate. Find out more about Ollas on the Lovely Green’s blog.


Using the same attitude as the Ollas, some people have set up ingenious systems using a wicking material, a water source and the capillary effect that plants can exhibit. As these systems don’t rely on a force to push the water through (instead it is pulled to where it needs to go) it is easier to make use of waterbutts and other water overspill in places like allotments.

These self-watering systems are great for containers, but probably not the most efficient method for watering large beds of crops. We found a forum thread that has a great example of using this method on a smaller scale, to water a few pots. It is easily set up with readily available materials.

Pre-Incan Irrigation

The most unusual system on this list is one that is too old to be innovative and has only recently been unearthed again. Looking at the farming techniques of ancient civilisations in South American countries, archaeologists and ecologists alike are looking to unearth information about growing in arid climates (which is becoming ever more pressing as climate change progresses). Looking at the canals and terraces that are believed to predate the Incan people, some keen gardeners are translating these techniques to their tunnels.

Steve James pioneered this technique with his designs in Scotland that utilize a central canal of water which is overlaid with a walkway, with raised beds on either side. Much like the self-watering solutions, the plants can wick away liquid as and when it needs it. The central canal also acts as a heat sink, maintaining warmth in the soil through the night while also helping to keep it cooler through the day.

Image Credit: 231/365″ by tamra hays is licensed under CC BY-NC-SA 2.0