Whether you own a glass or plastic greenhouse it can easily overheat when the weather is too hot. To protect your plants from overheating you need to provide good ventilation and shading.
There are many ways of shading a greenhouse, but today I want to talk about the greenhouse shade netting. Let's start with the quick introduction to what shading is.
Shading is a way of keeping the greenhouse cool during the hotter months. It reduces the temperature inside by minimizing the amount of light passing to the greenhouse.
You might think that good ventilation is enough to keep the temperature to the optimal value, but you are forgetting about the radiant energy from the sun.
It easily builds up inside the greenhouse and increases the temperature which is dangerous for many plants. Of course, the growth of plants directly depends on the amount of sunlight, so keep shading to the minimum.
As I have already mentioned the radiant energy from the sun heats the greenhouse. Particularly the infrared radiation. It is not visible to the human eye as it has longer wavelengths as those of the visible light.
For the active photosynthesis plants need blue to red range lights of the total light spectrum which are within 400-700 nm range. Anything higher than this range is damaging for the plants.
Exposure to the excessive amounts of the infrared light, particularly in the far end of the spectrum can damage the plants. It can be anything from discoloration to the to early growth spurts which impact on health, or can even lead to the death of plants.
Greenhouse shade netting reflects the sun rays back or partially blocks them. Plants only need 1.5-2% of the transmitted sunlight for the photosynthesis.
Shade nettings typically reduce the light level by 75% and turn it into the heat. The temperature of the netting raises as it acts as a solar collector.
The temp of the netting is higher than temp of the air, so the heat energy goes up. As it goes up, the cool air draws from below in the process known as evaporative cooling.
The most common materials for the netting are polyethylene and polypropylene. You can find a variety of shade nettings of different densities and degrees of shade ranging from 5 to 95 per cent.
A good shade netting should be water resistant to work well when it is raining or you are using an irrigation system to water your plants.
A waterproof shade netting is made of the 90 per cent shade fabric treated with UV stabilized resin to make it water resistant.
Today, you are most likely to find two types of shade nettings on the market: knitted and woven.
Knitted is constructed from the polyethylene and it looks like one continuous yarn is looped to form something similar to the tiny rows of braids.
Woven is made from woven polypropylene and represents multiple yarns crossing each other at right angles to create the grain, like a basket. The lifespan of the woven shade netting is from 10 to 12 years while the knitted one lasts 7-10 years.
The woven shade netting is typically 30% heavier than knitted one, hence tends to be more expensive. Also, the lightweight knitted option is easier to install. Both types are UV resistant and can withstand the extreme sun exposures.
The woven shade netting is only available in black colour. Knitted ones come in the variety of colours. The main difference between the both options is that woven will unravel if cut.
This is due to the structure of the netting. If a hole forms in the knitted shade netting the threads running in different directions will not unravel.
Moreover, knitted option is resistant to the most of the horticultural chemicals and detergents. The knitted fabric can be stretched up to 3 per cent whilst woven can't.
Overall, woven shade netting has multiple applications in wind screens, pet kennels and patio shading whilst knitted shade netting is widely used for a greenhouse shading.