As climate change continues to alter the UK’s weather patterns, weather extremes are becoming more and more common. It is not just extreme cold or wet conditions that can pose a problem for polytunnel gardeners. Extreme heat in a polytunnel can also be an issue during the summer months. While most of us are less inclined to worry about a heatwave than a storm or deep freeze, extreme heat can be just as damaging to our plants.
Extreme Heat in A Polytunnel – How Hot Can It Get?
If it is sweltering outside, inside a polytunnel it will, of course, be even warmer! The sun will raise the internal temperature of a polytunnel considerably. A polytunnel that is sealed and shut up can see temperatures soar to well over 30 degrees C – above the ideal temperature range for many common polytunnel plants. Some gardeners have chosen to embrace the heat – choosing to use their polytunnel as a sort of sauna, or for a hot tub or swimming pool.
How To Bring Temperatures Down
Regulating temperature in a polytunnel is largely a matter of regulating the airflow through the structure, and the humidity (moisture levels) in the air. You can also bring temperatures down by reducing the quantity of solar energy that is allowed to enter the structure (or reach certain plants).
To bring temperatures down in a polytunnel we:
- Improve ventilation.
- Damp down (water hard surfaces to raise humidity).
- Create shade.
You can use planting to create shade, or add shading by means of a additional area of cover on the south side of your polytunnel.
Ventilation in a Polytunnel
Having doors at both ends of a polytunnel is a good idea as this will allow for a through breeze which will aid in natural ventilation. If you have yet to purchase a polytunnel and think you may experience extreme heat in the summer, you may also consider having double doors, or larger sliding doors on the ends of your polytunnel, in order to maximise air flow through the structure. Certain planting outside your polytunnel can also help to funnel summer breezes through it to keep it cool.
When planting, take care not to try to cram in too much. Overcrowding your plants can lead to problems with air flow and ventilation which can make plants more prone to disease and more likely to succumb to various problems.
Keeping everything ship-shape can also help to ensure that your air flow is maintained over time. Stacked pots, piles of tools and general clutter and debris can reduce the efficiency of natural ventilation patterns in your polytunnel. Keep everything tidy and in order and you will find that everything in your polytunnel goes a lot more smoothly.
How do you keep your polytunnel cool in summer? Let us know in the comments below.
Elizabeth Waddington is a writer and green living consultant living in Scotland. Permaculture and sustainability are at the heart of everything she does, from designing gardens and farms around the world, to inspiring and facilitating positive change for small companies and individuals.
She also works on her own property, where she grows fruit and vegetables, keeps chickens and is working on the eco-renovation of an old stone barn.