Heat vs Light: Why Shade Nets Are Important

To make vegetable production growing systems work in a greenhouse in the Philippines, it is important to manage the balance between light and heat inside the greenhouse. Plants need light for photosynthesis, but too much sunlight brings about excessive heat which is detrimental to the growth of a young vegetable plant seedling. Adding shade nets over the grow areas is a must, but how do you know if it’s enough? Let’s start first by understanding how light and heat affects plants.

 

 

Full sun on the left, shade nets on the right

PHOTOSYNTHESIS

Photosynthesis is defined as the process in plants by which carbohydrates are produced from carbon dioxide and water using light as an energy source. Carbohydrates provide the building blocks for plant growth. Photosynthesis takes place on the leaves of the plant and only when there is light. Without either carbon dioxide, water, or light – photosynthesis cannot occur.

 

CAN PLANTS GET TOO MUCH LIGHT?

Young plants need less light than older, mature plants. Seedlings thrive better under low-level natural light (shaded) environments than under the full intensity of the sun. This is because, under full sun, the heat energy of the sun’s intensity on the plant surface area will cause the plant to use up the moisture to cool its plant tissue rather than effectively transpire and facilitate the photosynthesis process. Having too much shade is also undesirable because if the seedling doesn’t get enough light, the cells in the plant stem will elongate and “reach” for the light source. For green leaf vegetables, this produces unwanted results.

 

GREENHOUSE SHADING

 

In our greenhouse experiment, we used a light meter outside under the full rays of the sun and measured about 100K lux. This reflects the highest potential of heat energy transfer onto a plant leaf’s surface. Vegetable plants grown under these conditions will not grow optimally. Inside the greenhouse, we used an aluminum shade net below a layer of 8 mil (200 micron) UV polyethylene plastic for roofing and resulted in a reduction of light to 22 – 35K lux throughout the sun’s trajectory over the greenhouse. The resulting temperature drop went from 36C to 31C with the use of aluminet shading.

To buy a digital light meter, click here.

For those with hydroponics grow systems, plant growth problems persists when the temperature of the nutrient solution reaches high temperatures. This results in pervasive root rot and other problems that is disastrous to an entire crop. That’s why it’s very important to use shade nets over the greenhouse and to insulate the water reservoir against the sun either by burying the reservoir sub-surface or covering the reservoir with insulation material.

For seedling nurseries, shade nets are an indispensable tool to promote healthy seedlings. Exposed outside without protection from the elements, the seedlings wont grow to its fullest potential not to mention the increased level of care needed to irrigate the seedlings. Reducing the sun’s exposure with shade nets limits the leaf’s surface temperature while still diffusing enough light inside the nursery to promote healthy photosynthesis.

To buy shade nets, click here.

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