How lighting boosts greenhouse productivity

Supplemental lighting in hydroponic greenhouse systems can contribute significantly to the quality of produce grown in such systems, but it has to be utilised optimally as it adds significantly to the capital outlay and running expense of such a facility.

- Jeanne van der Merwe

To the uninitiated, it can be difficult to understand the need for lighting in a greenhouse. The bright white plastic and netting used for the flooring, walls and roofs of contemporary plastic greenhouses make the interiors of these structures almost unbearably bright.

“Plants make use of different (light) wavelengths to grow and photosynthesise,” explains Kaylee Smit, chief cultivation officer at Cultura Fresh, a hydroponic vegetable producer supplying national retailers from farms in Klapmuts and Stellenbosch.

“Each growth phase of the plant (germination, seedling, vegetative, flowering or reproductive phase, and the maturation or harvest phase) requires a different light wavelength and a different set of climatic conditions for the plant to thrive,” she says.

While there are indoor farming industries that rely solely on artificial lighting, the establishment and running costs make them prohibitively expensive in South Africa for all but the most high-end horticultural industries, notably cannabis.

“In South Africa we have very good sunlight, so we generally use artificial lighting to supplement sunlight rather than to replace it,” says Jonathan Adams, technical manager at Vegtech Netafim, a designer and builder of greenhouses and provider of greenhouse technology.

“In developed countries, which typically receive less sunlight and have better access to capital and finance, commercial farming exclusively under artificial conditions is more feasible than in South Africa,” he explains.

Modern greenhouses are designed to optimise solar light that plants receive.

“The white polyethelene thermo plastic used on the exterior of greenhouses has good light transmission and diffuses the sunlight, so it spreads evenly to all the leaves without sharp shadows. The white ground cover reflects light to the underside of the leaves and maximises photosynthesis throughout the plant,” adds Adams.