As summer approaches, we need to get our gardens ready for long, hot and sunny days. One way to go about this is to move some of the more sensitive species under shade covers.
But what type of cover will work best? What will my plants need? Can I not just use some netting? We will be answering all these questions and more!
What is shade cloth?
Shade cloth is essentially a matrix of fibres that can block harmful UV sun rays. When you are a first-timer, it is possible to get confused between various products. There are several classes of shade cloth on the market. These include shade cloth for recreational areas, privacy screens and plant protection.
Plants require sunlight (within the visible range), but not necessarily heat and harmful UV wavelengths that will burn the foliage.
For more on sunburn and sun stress in plants, dig into the article below.
Types of shade cloth
There are two classes of shade cloth, namely high-density polyethylene (HDPE) shade cloth and polypropylene woven cloth. Greenhouses tend to be constructed from knitted HDPE, whilst woven polypropylene cloth is heavier and provides better UV protection.
Two properties you need to consider before buying:
1 - Weave density (also referred to as shade percentage)
2 - Colour of the material
These two will be discussed separately below.
What does the percentage mean?
The percentage gives you an indication of how tightly the material is woven. This will affect the amount of shade it can provide.
Tips on selecting shade cloth:
- Lower is better: You want shade, but not too much shade.
- Location: The sun exposure in Durban vs Upington is different and will require different approaches.
- Roofing vs cloth: Polycarbonate roofing usually has a built-in 99% UV protection but will let heat and other wavelengths through. Covering the roof with shade cloth may reduce the temperature.
- Shade vs Frost cloth: Frost cloth is white polypropylene with tiny holes and should not be confused with shade cloth.
- Plant species: As with grow lights, it is important to know your plants and the light levels they require.
Which colour to choose?
The colour might seem trivial, but in practice, the colour of the shade cloth will often dictate the percentage of shade it provides (1). In other words, a 20% shade cloth can provide between 12-20% shade depending on the colour. The reason behind this is that different colours will absorb (e.g. dark colours) or reflect (e.g. light colours) sun rays.
Tip | White cloth will reflect light and is better for ventilation, whilst black will absorb light and hold its heat.
Michigan State University conducted a study on the effects of various light wavelengths (colours) on how fast seedlings grow (2). They determined that green and blue light suppressed the growth of some species.
Using shade cloth in greenhouses
It is a well-known fact that covering a greenhouse with shade cloth will reduce the temperature. It is advisable to leave some space between the cloth and the greenhouse structure. If you place the shade cloth inside the greenhouse, the air will essentially bake and become extremely hot.
Here is a quick reference to what is deemed executable for certain groups of plants. Mind that this generalisation is subject to individual species growth requirements.
20-50% shade Green:
75% shade Green:
(1) Stephens, W. (2007). Coloured shade cloth and plant growth. In Combined Proceedings International Plant Propagators‟ Society (Vol. 57, pp. 212-217).
(2) Wollaeger, H. & Runkle, E. (2014) Green light: Is it important for plant growth? https://www.canr.msu.edu/news/greenlightisitimportantforplantgrowth
(3) Willits, D. H. (2003). The effect of cloth temperature on the cooling efficiency of shade cloths in greenhouses. Transactions of the ASAE, 46(4), 1215.