Yes they can. During summer it’s important to monitor your greenhouse temperature (this can easily be done by installing a thermometer inside your greenhouse) and make sure it doesn’t get too hot. It depends on which plants you’re growing, but in general and in the average climate, the hottest summer days can be too hot for your plants to survive in. Luckily there are enough ways to bring the temperature down. You can choose to use a shade cloth to protect the greenhouse from direct sunlight and you can ventilate your greenhouse. The easiest way to ventilate your greenhouse is by opening the windows or doors by hand, but you can also install a hydraulic system that opens the windows automatically. These hydraulic systems will open the windows when the temperature rises above a certain level and will close them again when the temperature decreases.
Take a look at our article about greenhouse shade cloths, to help you cool down your greenhouse!