Property North Wales

Look After Your Greenhouse: Ventilation & Shading

With summer well and truly here (for the most part!), it’s time to consider your greenhouse. Whether it is made of glass or plastic, it can easily overheat in sunny weather. Your plants can be protected from excess heat through appropriate shading and ventilation. This is where your green house staging can come in useful, their tiered structure allows plants to be placed in the shade with ease. 

When to Ventilate & Shade Your Greenhouse

Greenhouses are very vulnerable to overheating from Spring until the Autumn. Without some protection from the heat, very few plants are likely to survive unharmed when they are being subjected to prolonged high levels of heat and dry atmosphere within your greenhouse.

However, with the introduction of sufficient air circulation, shading and humidity, many of your plants will be able to tolerate high summer greenhouse temperatures in the same way that they would be able to handle life in the tropics - where many greenhouse plants originate from. 

For gardeners, the main aim is to prevent leaf temperatures from rising to a level where tissue damage occurs. As the months continue into September, shading should be gradually reduced and then removed completely when ventilation alone can control overheating. The blinds and netting used during the summer to aid with shading can be used on colder winter nights to limit heat loss. 

How to Ventilate & Shade Your Greenhouse

Leaf temperature is mainly controlled by the movement of water through the plant, and out of the plant through the leaf surfaces during a process called transpiration - this process is known to have a cooling effect on the leaves. 

Plants which are dry at the roots or drying out are more at risk than plants that have adequate moisture at the roots. Air movement is another important factor to consider, as air movement over the leaf surfaces also has the ability to provide a cooling effect. 

  • Ventilation

There are usually three different areas in a greenhouse where air and come in and out:

  1. The door (either single or double)

  2. The roof vents (sometimes these run the full length of the ridge and are either opened manually or with automated openers)

  3. The side vents (these are often louvred)

Interestingly; with larger greenhouses, one square meter of ridge ventilations for every five square meters (20%) of floor area, provides the ventilating capacity to give one complete change of air within the greenhouse every two minutes. 

Effective Ventilation

  • Open all doors and vents on sunny days. These can also be left open at night if the temperature remains high. 

  • Be alert and aware of the signs that shading and ventilation are required; sun-flag (partial collapse), leaf scorch, desiccation of tender young plants and shoots. 

  • Monitor greenhouse temperature with a maximum-minimum thermometer. If the temperature is allowed to build up (typically more than 27 degrees), then plant damage can occur. 

  • In unpredictable weather, vents and doors often need to be left partially open to limit sudden increases in temperature. 

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