Light And Its Effects On Plant Growth

The most important variable affecting plant growth is light exposure, and it is therefore important to measure the amount of light your plants receive. Prof Gert Venter explains how this is done.

- Prof Gert Venter

The most important concept to understand when growing plants is the rule of limiting factors, which determines plant quality. Hydroponics cannot compensate for poor growing conditions, such as improper temperature, insufficient irrigation, nutrient deficiencies, pest and disease problems, or poor light.

Light is the most important variable influencing plant growth.

If plants do not receive enough light, they will not grow at their maximum rate or reach their maximum potential, regardless of how much of any other variable – water, growth medium or fertiliser – they receive.

INCREASING LIGHT INCREASES YIELD 

Light is the driving force for photosynthesis, a plant process that changes sunlight into chemical energy. During photosynthesis, water is split in a chemical reaction in which it is separated into oxygen and hydrogen, and carbon dioxide (CO 2) is converted into sugar. A general rule of thumb is that 1% more light will give you a similar percentage increase in plant growth, resulting in a 1% higher yield.

All plants require light and CO 2 for photosynthesis. Adequate spacing between plants will ensure that each plant receives sufficient light in the greenhouse. Tomato plants pruned to a single stem are spaced at 2,7 plants/ m 2 to three plants/m 2 . Seedless cucumbers, with their larger leaves, require almost double this spacing. Hydroponic lettuce spacing varies from 2,5cm 2 for first-stage seedlings to 15cm 2 for final spacing.