How to Keep Cool in a Polytunnel

Learning how to keep cool in a polytunnel in summer is crucial if you want to enjoy the space, and grow your own food and other plants successfully. 

Learning how to keep cool in a polytunnel might involve thinking about good ventilation and air flow from the outset. It can involve good design choices for the internal layout of the space. And it can mean taking other steps to lower temperatures within an existing structure. 

Here are some tips to help you keep those temperatures from soaring in the summer months:

If You Have Just Purchased a Polytunnel:

If you have only just bought or erected a polytunnel, or are planning to do so soon, it is important to make good decisions from the very beginning. Prevention is better than cure when it comes to keeping a polytunnel cool. 

There are steps that you can take when deciding on options for the structure. You can also cut problems off at the pass by positioning your polytunnel correctly. 

Ventilation for a Polytunnel

When thinking about ventilation for a polytunnel, it is important to consider how the polytunnel will be used. Making sure you keep cool within the space can be particularly important if keeping livestock, or growing cooler climate crops within the area. 

Of course, how much ventilation is needed will also depend on where you live. Some parts of the UK will naturally get much warmer than others. 

Are the doors alone enough to provide ventilation through the summer, or should you consider side ventilation too? Asking questions like this is important to prevent problems down the line. 

Orientation for a Polytunnel

Another key thing to consider is the positioning of your polytunnel. There are a number of things to think about when selecting where to place a polytunnel, and deciding which way it should face. 

One important factor to take into account is the orientation of the doors. By positioning a polytunnel to take advantage of prevailing summer breezes, you can make sure that there is good airflow through the structure. This will help you to keep cool in a polytunnel through the summer months.

Designing the Interior of a Polytunnel:

Next, you should turn your attention to the design for the inside of your polytunnel. No matter how you plan to use the space, good design choices can be key. 

Think carefully about how you plan to use the space, and the temperatures that you therefore require within the structure. Practicality is key to good polytunnel design. 

Ensure Easy Access to Open and Close Doors/ Vents as Needed

It is essential to be able to regulate the temperature within a polytunnel – especially over the summer. But in the summer, growers will often find that the space becomes crowded as plant growth explodes. 

To keep cool, avoiding stress and hassle, it is important to have a well-worked-out scheme, with good access. This will stop you from getting flustered, raising the heat still further. And it will ensure that you can easily alter ventilation as required. 

Add Thermal Mass

Another very important thing to consider at the design stage if you want to keep cool in a polytunnel is thermal mass. To keep cool in a polytunnel, incorporate materials with high thermal mass. 

These materials, like stone, brick, ceramic and clay, water and soil, are good at catching and retaining the sun’s heat during the day. They then release that heat at night, when temperatures fall. 

So they can keep the temperatures more constant over time. They help things keep cool in summer, and reduce issues with cold in the winter months. 

How to Keep Cool in an Existing Polytunnel:

If you have a polytunnel already, you can still consider adding thermal mass. You might incorporate it through improvements to pathways, in bed edges, in staging, or simply be adding a feature like a water barrel or tank inside the space. 

But here are a few other ways to make sure you can keep cool in a polytunnel, even during a more extreme heat wave:

Make an Evaporative Cooler

Making a DIY evaporative cooler for the space is one way to come with weather extremes. An evaporative cooler can be a complex piece of equipment. But it can also be a very simple solution.

For example, you might place a tray of water with a rag within it in a breeze. As the water evaporates from the material, it will cool the air of the surrounding area. 

Another easy hack is simply to dry some laundry in the space. This is a good way to kill two birds with one stone. Your clothes should dry more quickly than they would outside, and as the water evaporates from the material, this should cool the space to a degree. 

Increase Humidity by Spraying Paths and Surfaces

On hot days, you can also spray down or sluice hard surfaces within the structure, such as pathways or staging. This will certainly help you keep cool in a polytunnel when maintaining the space on hot days.

Again, the cooling effect is about the water evaporating. Though of course, in low-water areas where there could be drought, splashing lots of water around is unlikely to be the best solution. 

Cool Your Polytunnel With a Fan

If things get really stifling, you might also consider cooling your polytunnel with a fan. If you are looking for an eco-friendly and sustainable option then you should consider a fan which runs off solar energy. And add a PV panel close by. 

Take Steps To Reduce Soil as Well as Air Temperature

Remember, learning how to keep yourself cool in a polytunnel in summer will dramatically improve your gardening experience. But it can also ensure the requisite conditions for plants (or any animals) within the space. 

Plants can be negatively impacted not only by air temperatures that rise too high but also by high soil temperatures if you don’t keep cool in a polytunnel.

To keep the soil cool in a polytunnel:

• Create beneficial micro-climates and areas of shade with planting or internal structures.
• Keep living roots in the soil through as much of the year as possible. 
• Use mulches of organic matter between your plants. 

These are just some tips to help you make sure that you, and other living beings within the space, keep cool in a polytunnel throughout even the warmest parts of the year.