Mike Straumietis: How Does Light Affect Plant Growth?

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Several environmental factors affect plant growth, explains Mike Straumietis, Founder and CEO of Advanced Nutrients. These include nutrition in fertilizers, temperature, and crop quality, to name a few. You may manipulate plants to meet your needs with even a basic understanding of these factors. By identifying these factors, you’ll be better equipped to diagnose plant problems caused by the environment.

In this blog post, Mike Straumietis discusses one major environmental factor affecting the growth of plants – light.

When looking at light as an environmental factor affecting plant growth, it is important to note three main characteristics: quality, quantity, and duration.


The quality of light refers to the color or wavelength of light. Sunlight supplies the complete range of wavelengths — bands of red, orange, yellow, green, blue, indigo, and violet. Plants absorb blue and red light. Therefore, these lights have the greatest effect on plant growth. Blue is responsible primarily for vegetative (leaf) growth, while red encourages flowering when combined with blue light. 

Fluorescent or cool white light is high in the blue wavelength. It encourages leafy growth and is ideal for starting seedlings. Incandescent light has a lot of red or orange lights. However, it generally produces too much heat to be a valuable light source for plants. 


The quantity of light quantity means the intensity or concentration of sunlight, which varies with the seasons. The maximum amount of light is available during the summer, while the minimum amount can be found in the winter. The more light a plant receives from the sun up to a certain point, the more food it can produce through photosynthesis.

Mike Straumietis points out that you can manipulate light quantity to achieve different plant growth patterns and results. You can increase light by surrounding plants with reflective materials, white background, or supplemental lights. You can reduce light exposure by shading plants with cheesecloth or woven shade cloths.

Duration, in the context of light, is also called photoperiod. Photoperiod is defined as how much time a plant is exposed to light. The amount of time controls flowering in many plants. 

It is interesting to note that scientists and researchers once thought that the length of the photoperiod triggered flowering and other responses within plants. This is why they describe plants as short-day or long-day, and it depends on what conditions they flower under. However, in more recent studies, researchers observed that it is not the length of the photoperiod but rather the length of uninterrupted periods of darkness that is crucial to floral development.

Plant Classification

As mentioned earlier, plants are categorized into three types. There are short-day (long-night), long-day (short-night), and day-neutral. They are classified on how they respond to the duration of light or darkness. 

For example, short-day (long-night) plants form flowers only when the day lasts less than 12 hours. Many plants that flower in the spring or fall are in this category. Meanwhile, long-day plants form flowers only when the day length exceeds 12 hours. Most of the plants that flower in the summer are long-day plants. Plants that are day-neutral aren’t dependent on day length.

Some plants don’t fit into any category but may respond to combinations of day lengths. An example would be petunias, which bloom regardless of day length but do earlier and more profusely with long days, Mike Straumietis explains.

 Manipulating Light and Plant Growth

You can manipulate photoperiod to stimulate flowering, notes Mike Straumietis. For instance, chrysanthemums usually bloom in the short days of spring or fall. You can get it to bloom in midsummer. You have to cover them with a cloth that completely blocks light for half a day. You’ll see that after several weeks of doing so, the artificial dark period will no longer be needed, and the plant will bloom as though it were spring or fall—growers who make poinsettias flower in time for Christmas using this method.

If you want a long-day plant to flower when the day length is less than 12 hours, you can expose the plant to supplemental light. After a few weeks, you’ll most likely notice flower buds forming, Mike Straumietis explains.

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