Polytunnels – Your Guide To Managing Yours During an Irish Summer

Now you have your Polytunnel, what to do if we get a proper Summer..not just a few sunny days…with those black clouds in the distance! If the weather person mentions High Pressure or even Heatwave, you need to be prepared. A heat wave can wreak havoc on your crops. Especially if they’re grown in a polytunnel. Of course, when the weather outside is hot, temperatures within a polytunnel can rapidly become oppressive.

Working within a polytunnel might be tough during hot spells. But, more importantly, it can endanger your plants. Remember, humans can get out of the heat quickly if it gets too hot – but plants can’t! Continue reading for more helpful hints.

1. Plan Your Planting for the Summer Heat Wave Months Appropriately

To begin with, careful planning and preparation are required to avoid complications when temperatures become high. As global temperatures continue to climb, most of us will certainly experience hotter summers in the future years. When deciding which plants (and cultivars) to grow in your polytunnel, this is definitely something to think about.

Heat and watering go hand in hand, so for the period when you expect greater temperatures, consider choosing ones with reduced water requirements.
Another crucial consideration is how you combine various plants. Consider tall or vining plants to give shade for green lettuces, spinach, and other crops that may bolt in hot weather. During a heat wave, plant shade may be critical.

2. Keep an eye on weeds and make sure plants aren’t overcrowded.

In a polytunnel garden, companion planting might be crucial to success. But be careful not to overcrowd your polycultures with plants. Growing areas should be properly developed to maximize space while avoiding overpopulation. This can be a tricky balancing act at times.

Overcrowding can cause plants to become stressed in high temperatures, which can lead to an increase in disease and pest problems. Keep an eye out for weeds as well. Weeds aren’t always a problem, but they can be if they outcompete your crops or harbor or attract pests. The majority of common polytunnel crops require a specific temperature range. When the temperature within the polytunnel rises beyond 35 degrees Celsius, you may notice a variety of problems. The more you can do to maintain your plants healthy and vigorous, the better chance they’ll have of surviving the heat.

3. During a heat wave, increase the amount of water you provide.

This may seem self-evident, yet many gardeners overlook the impact that temperature has on the water requirements of various plants. Make sure you water as often as necessary, and that you know which plants require the most and which require the least.

It’s also crucial to get the water to where it’s needed, which is around the roots. Watering from above may result in less water getting to where it is needed. Watering leaves can also burn them, especially in extremely hot and bright conditions.

4. During a heat wave, make sure you mulch around your plants.

Mulching is usually a smart move. However, it is especially critical when hot weather is forecasted or when a heat wave occurs. A thick layer of organic mulch around your fruits, veggies, and other plants can aid in the addition of slow-release fertilizer. It will add nutrients to your growing regions as it decomposes. Another strategy to keep plants as healthy and strong as possible is to use this method.

Importantly, this will aid in moisture retention, ensuring that the soil in your beds and other growth areas does not dry out as rapidly. In addition, your polytunnel’s irrigation requirements will be lowered.

5. If you don’t already have it, consider adding automated irrigation.

During a heat wave, you may find that you need to water your polytunnel plants more than once a day! If you’re watering everything by hand, it can be difficult to keep up. If you don’t already have it, automated irrigation for your polytunnel might be an excellent option.

However, there are additional steps you may do to make your life easier. Sinking pots into the soil at the base of plants, for example, allows you to water directly into the vessels, ensuring that the plants’ roots get the water they require. You may also think about using clay pot irrigation. You might also use watering globes (or bottles that perform the same purpose) to provide plants with water as needed.

6. Ventilation

The amount of ventilation in your polytunnel will be determined by its features. When the weather gets particularly hot, some polytunnel designs allow you to open up vents and promote airflow. At the very least, make sure the tunnel’s doors are open on both ends to allow air to pass through.

Thinning and selective pruning can also help your polytunnel’s circulation and air flow. So, if something appears to be a bit clogged, get in there and clear it up a little. Make sure you keep your polytunnel neat as well; don’t leave tools or pots laying around that could obstruct air flow.

7. To Control Temperatures, Add Thermal Mass

Working to improve temperature management in your polytunnel is another technique to ensure that temperatures do not spiral out of control. You can keep the temperature of your polytunnel more steady by using passive solar design concepts.

Thermal mass (materials that are good at capturing and storing heat energy from the sun) is ideal for temperature control. These materials, such as water-filled containers, stone, brick, and clay, absorb heat throughout the day, keeping the air cooler, and then gently release it at night as temperatures drop.

8. In a heat wave, consider using a solar-powered fan to improve air flow.

If your polytunnel is truly suffocating, you might want to consider putting in a solar-powered fan to help circulate air. You might also try evaporative cooling by combining a fan with a box filled with damp cloth/material. There are a variety of DIY options available to assist you in building your own basic polytunnel air conditioner.

9. To Reduce Heat Wave Temperatures, Dampen Hard Surfaces

In your polytunnel, raising humidity is another way to deal with a heat wave. Using water, wet down your pathways, staging, and other hard surfaces. The cooling impact of the water will be felt when it evaporates.

10. Consider Adding Shade Netting to Exclude Sunlight During the Hottest Portion of the Day

If you’ve tried everything above and your polytunnel is still too hot during a heat wave, you might want to consider adding shade netting to exclude sunlight during the hottest part of the day. You might use shade cover to block sunlight from entering your polytunnel entirely, or you could use it to protect specific plants within the space.

These are just a few options for dealing with a heat wave in your polytunnel. However, it is always preferable to anticipate and plan for an issue rather than attempting to solve it after it has arisen.

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