Many of our favorite vegetable plants are adversely affected by sunburn, heat stress, poor yields and quality due to environmental factors. It’s not only commercial growers that need to protect their crops from these problems; home gardeners need strategies to optimise their harvest. Many places worldwide are facing hotter and drier growing conditions. So, it’s essential to find ways to protect our edible crops to minimise damage, improve growth and harvests.
Like many gardeners, I’ve battled intense UV rays, heat waves, and drying winds in our subtropical climate for years. High temperatures (35–40°C) caused by increased solar radiation can devastate plant growth and reproductive development. While plants need sunlight to photosynthesise, too much light and heat can cause crops like lettuce, rocket and coriander to bolt quickly. Using microclimates with filtered light is an excellent strategy, and shade cloth can help.
Considerable research into using shade cloth in different colours and shade ratings provides insights into a viable solution to some of these challenges. Multiple studies (2) reveal improved yields and quality of many crops, including fruits, vegetables, ornamentals, herbs and tea.
How Does Shade Cloth Work?
Using shade cloth enables us to control the microclimate conditions under which plants grow. We can safeguard crops from potentially damaging environmental conditions, including excess sunlight radiation, drought, high temperatures, frost, drying winds, hail and flying pests.
Shade cloth is made from various materials, including polyethylene, polypropylene and polyester or acrylic by-products. Netting varies in light transmission rates, reflection and absorption of light, and air permeability depending on the shade intensity and colour.
The higher the shade factor of the woven fabric, the more radiation is blocked.
Knitted shade cloth is ideal for home gardens because it is hardwearing, long-lasting, UV-resistant, lightweight, and easy to handle. It is made from polyethylene, which deflects light and heat.
The density percentage refers to the level of sunlight that is blocked. For example, 30% shade cloth stops 30% of the sunlight from penetrating the plants underneath. This density suits many fruiting crops that can tolerate heat. Heat and light-sensitive plants like lettuce and leafy greens grow well under higher density shade of 50% without harming growth.
It’s a balancing act between plants receiving sufficient energy from the sun to photosynthesise and enough shade relief to mitigate potential damage.
Does the Colour of Shade Cloth Matter?
The research confirms yes! White shade cloth reflects heat and light, making the temperature cooler. Darker colours, like black, absorb the sun’s heat while filtering the light.
Neutral shades (black, grey and white) reduce the quantity of light that reaches plants. Whereas coloured photo-selective netting (blue, red, yellow and pearl) diffuses or filters out different light spectrum wavelengths. The pearl net scatters light to a greater extent than any other colour.
Coloured shade cloths filter light in ways that affect plant responses. Light affects plant photosynthesis, leaf growth and size, crop size, yields, and phytochemical production.
For example, one study (5) reveals that red and yellow nets stimulate the vegetative growth cycle and foliage vigour on cilantro-coriander, parsley, and basil. Meanwhile, blue netting was found to stunt growth and decrease yields. The research concludes that various plant species respond differently under different coloured nets.
It is clear from the various studies that no one-size-fits-all shade cloth optimises the results for all plants! Each species has a complex interaction with light. One study (4) explains that “plants respond to light quantity, quality, direction, and periodicity. There are numerous photoreceptors in plants, including chlorophylls, phytochromes, cryptochromes, phototropins, and ones that react to green light. Light and other environmental cues enable plants to adapt to environmental conditions.”
Key Findings on Popular Crops
There’s a wealth of research across a wide range of crops. These are a few results for some of our favourite vegetables.
Capsicums
Research(1) on bell peppers (capsicums) found that yields improved significantly under 35% black shade cloth compared to unshaded plants. The plants were less prone to blight and sunscald. “Optimal shade level for maximal fruit yield was that which maximised the cooling effect resulting from the reduction of infrared (IR) radiation and minimised the decrease in net photosynthesis resulting from a reduction in photosynthetically active radiation (PAR).”
Interestingly, the soil temperature under shade cloth was reduced to the optimum temperature of 27°C. Additional benefits of shading peppers include less moisture loss and an extended harvest season. Capsicums had the best yields and quality under 30-47% shade cloth(1).
Lettuce
Another study(3) confirmed 37% shade under red nets to 55% under black nets provided optimal light conditions for growing lettuce in summer. The leaf size increased, heads were bigger, and outer leaves were greener, softer and more tender than non-shaded lettuce. Nutritional content was significantly higher in non-shaded control plants and under the pearl colour than in other nets.
Tomatoes
Responded best under 35%-50% shade intensity netting with pearl and red colours achieving the best overall results. Red shade cloth had the highest nutritional results(6).
Cucumber
Yields were highest under pearl shade cloth(7).
Advantages of Shade Cloth
Many studies reveal consistent results and benefits over a wide range of crops. Overall, shade cloth nets of any colour with moderate shading (30-50%):
• Prevent fruiting crops from suffering sunburn.
• Decrease moisture loss and water stress.
• Increase water use efficiency in plants.
• Protect crops from excessive solar radiation and insect, bird or hail damage.
• Modify the air, plant and soil temperature, shade and humidity growing conditions.
• Increase the size and colour of leaves.
• Control light quality by increasing diffused (scattered) light.
• Enhance the quality and yield of many crops.
• Reduce watering requirements.
Shade cloth can be used on a small scale in home gardens in many ways. It can be installed over arches, vertical garden structures and as temporary, seasonal covers that can be rolled up and stored in the cooler months. I can’t imagine growing our summer garden without it. We want lots of leafy salad ingredients, but growing them is challenging in the heat.
What are the Key Takeaways For Using Shade For Vegetables?
- Using shade cloth provides distinct benefits for mitigating the impact of climate-related weather and growing conditions.
- Plant species respond uniquely to different coloured nets. Choose one that will protect the plants we want to grow.
- Studies(2) show shading can decrease air temperature by 1–5°C, reducing heat stress.
- For home gardeners, particularly those that experience hot summers with intense sunlight and heat, shade cloth at 35% shade level can provide some significant benefits for a range of crops(6) and particularly in a light colour.
References:
1. Bell Pepper (Capsicum annum L.) Crop as Affected by Shade Level: Fruit Yield, Quality, and Postharvest Attributes, and Incidence of Phytophthora Blight (caused by Phytophthora capsici Leon.) Hortscience 49(7):891–900. 2014.
2. Zhang Q, et al (2022) Color Shade Nets Affect Plant Growth and Seasonal Leaf Quality of Camellia sinensis Grown in Mississippi, the United States. Front. Nutr. 9:786421.
3. SZ. Ilić et al. Light modification by color nets improve quality of lettuce from summer production, Scientia Horticulturae, Volume 226, 2017, Pages 389-397, ISSN 0304-4238.
4. Use of Colored Shade Netting in Horticulture. Robert H. Stamps. Hortscience Vol. 44(2) April 2009.
5. Ilic, Zoran & Fallik, Elazar. (2017). Light quality manipulation improves vegetable quality at harvest and postharvest: A review. Environmental and Experimental Botany 139 (2017) 79–90. 139. 79-90.
6. Nangare, D.D. et al. (2015). Effect of green shade nets on yield and quality of tomato (Lycopersicon esculentum Mill) in semi-arid region of Punjab. Asian Journal of Advances in Basic & Applied Sciences. 1. 1-8.
7. Tafoya, Felipe et al. (2018). Sunlight transmitted by colored shade nets on photosynthesis and yield of cucumber. Ciência Rural. 48. 10.1590/0103-8478cr20170829.