Shading your greenhouse
Written by John Harrison on 8th May 2015.
Greenhouses serve to both extend the growing season and to provide better growing conditions during the season, enabling us grow tender crops such as tomatoes and aubergines even in a bad summer.
In a good summer though the greenhouse can become a very hostile climate to grow in. It's surprising how quickly the temperature can soar to levels that kill our plants as surely as if they were put in the oven. That same sunlight that powers photosynthesis and growth can turn to scorching, killing the leaves.
Ideal Greenhouse Temperature
The ideal temperature for a greenhouse is lower than you may have expected; between 20 and 24 degrees C. Temperatures above 27 degrees C should be avoided.
Good ventilation is critical to maintaining temperatures in the best range for growing. Automatic vent openers are really useful because it's always the day you're away or the morning you sleep in that the sun decides to over-heat the greenhouse. The automatic openers can save the day.
Summer Greenhouse Shading

When we do get a reasonable summer in Britain, which happens more than you might think, opening the vents will not be enough and we turn to shading the house. There are different ways to shade your greenhouse and all have their good points and bad.
Because all shading works by reflecting sunlight or preventing sunlight from reaching the plants and greenhouse base, there is less light and energy available to power photosynthesis.
Greenhouse Shading Paints
Whitewashing the outside of the greenhouse or potting shed will reflect sunlight and, therefore, prevent or at least reduce overheating and prevent the sun from scorching your crops. The most popular product for this is Cool Glass from Bayer.
It's fairly cheap to buy but it takes time to apply and it can be difficult to safely apply to the roof, especially with larger houses. The same applies at the end of the summer when it comes to removing the shade paint which is brushed and rubbed off.
Cool Glass does have a useful feature in that it becomes clear when wet so in rainy weather it allows all the available light through. As it dries it becomes reflective again.
Greenhouse Blinds & Net Shading

The cheap and cheerful solution, often seen on allotments, is to use green shade netting or even old net curtains draped over the greenhouse and tied in place with string. It doesn't look very pretty but it does the job.Care has to be taken that the netting does not obstruct vents, especially automatically opening roof vents, which would be counter-productive. Unless tied properly, they have a habit of blowing out of position or even completely off the house in even moderate winds.
Purpose Made Greenhouse Blinds
Purpose made external blinds that are drawn down or across the house are far easier to draw up in dull weather and down again in sunny providing much better control. They tend to be a fairly costly option but not so bad when that cost is apportioned over the life of the greenhouse.
Internal blinds tend to be cheaper but, as the sunlight has already come through the glass, less good at cooling the house than external blinds. The do have a benefit in that they provide some insulation value and keep heat in the greenhouse overnight.
Protecting Your Greenhouse Plants with Effective Shading
Greenhouse shading is crucial for maintaining optimal growing conditions during bright, sunny periods. Without proper shading, intense sunlight can scorch plant leaves, attract pests like red spider mites, and cause uneven ripening of fruits such as tomatoes and peppers. By providing appropriate shade, you can create an environment similar to a tropical rainforest, where plants thrive in filtered light and balanced humidity.
Effective Shading Methods for Your Greenhouse
1. External Shade Netting
A large sheet of plastic weave or hessian can be easily draped over your greenhouse roof. Secure it with clips or ensure it's large enough to reach the ground, where you can weigh it down with bricks or stones. This method offers flexible coverage that can be adjusted as needed.
2. Shade Paint
Greenhouse shade paint is a simple yet effective solution. Apply it to the exterior of the glass as needed. It's weather-resistant and provides consistent shading. Remember to remove it at the end of the growing season to allow maximum light during cooler months.
3. Internal Shade Netting
Plastic weave shade netting can be securely fastened to the interior of your greenhouse. This provides a neat solution that isn't affected by external weather conditions. Most greenhouses have standard clips that can be used to attach the netting to the frame.
Additional Tips for Plant Protection
- Water plants consistently to prevent dry roots, which are more susceptible to leaf scorch.
- Ensure proper ventilation by opening doors and windows. Air movement over leaves helps cool them down.
- Maintain humidity by keeping a bucket or watering can full of water in the greenhouse.
- Use a thermometer to monitor temperatures, aiming to keep them below 27°C (80°F).
- Consider installing automatic ventilation and shading systems for more precise control.
Seasonal Considerations
As summer wanes and temperatures cool, remove shading paint and adjust other shading methods. During colder months, keep blinds and netting accessible but out of the way, ready to be deployed when needed. This approach allows you to maximize light during winter while being prepared for sunny spells.
Greenhouse Shading FAQ
What is the best shading for a greenhouse?
The best shading for a greenhouse depends on your specific needs and climate. External shade netting offers flexibility and ease of use, while shade paint provides consistent coverage. Internal shade netting is neat and weather-resistant. For many gardeners, a combination of methods works best, allowing for adjustments based on the season and specific plant requirements.
Should you shade your greenhouse?
Yes, shading your greenhouse is often necessary, especially during bright, sunny periods. Proper shading helps prevent leaf scorch, reduces water stress on plants, and creates a more balanced growing environment. It's particularly important in regions with intense summer sun or for growing plants that prefer partial shade.
How to fix shading to a greenhouse?
Fixing shading to a greenhouse depends on the type of shading you choose. For external netting, use sturdy clips designed for greenhouse use, or weigh down the edges with bricks or stones. Internal netting can be attached using greenhouse frame clips or a wire system. Shade paint is applied directly to the exterior of the glass with a roller or sprayer. Always ensure your chosen method is secure and doesn't risk damaging the greenhouse structure.
What is the best shade percentage for a greenhouse?
The ideal shade percentage for a greenhouse typically ranges from 30% to 50%, depending on your climate and the types of plants you're growing. Sun-loving plants like tomatoes might need only 30% shade, while more delicate plants could require up to 50%. It's often best to start with a lower percentage and increase as needed, observing your plants' response to find the right balance.
When to put up greenhouse shading?
The timing for putting up greenhouse shading varies depending on your location and climate. Generally, it's best to install shading in late spring or early summer, as days become longer and sunlight intensifies. Keep an eye on your greenhouse temperatures and plant health. If you notice signs of heat stress or leaf scorch, it's time to add shading. Be prepared to adjust your shading throughout the season as light levels and temperatures change.
Copyright © John Harrison 2014