Answers to Your Questions: Do Houseplants Need Ultraviolet Light?

Question

I’m planning to install a film in the windows of my apartment to cut out ultraviolet rays. Will the houseplants survive? Do they need ultraviolet rays to survive?

Answer

Plants, like humans, can be damaged by ultraviolet (UV) rays, albeit to a lesser degree. However, it’s important to understand the role of UV rays and light in general in the growth of houseplants.

Plants mainly use visible light for photosynthesis, the process by which they convert light into energy. Blue and red light wavelengths are particularly crucial to this process. UV rays, although potentially damaging, play a more indirect role. For example, certain plants, such as cacti and orchids, require exposure to UV rays to develop a certain resistance and robustness. This exposure helps them to harden and better protect themselves against harsh environmental conditions.

Light Reduction

By installing UV protection film on the windows of your home, you reduce not only UV rays, but also some of the visible light that enters your space. This reduction in light can be problematic, as all plants need light to survive and thrive. Less visible light means less energy available for photosynthesis, which can lead to a general weakening of your houseplants.

For plants that need more light, such as cacti and orchids, the absence of UV rays can be problematic. However, the main concern lies in the reduction of visible light, which is essential for all plants. Your plants may indeed languish behind a window fitted with UV protection film if the amount of light required for their growth is insufficient.

Mitigate the negative effects of UV protection film

1. Choose a film that reduces UV while maximizing visible light transmission. Some films are designed to filter out UV while still allowing sufficient light through to plants.
2. Complement natural lighting with grow lights. Grow lights provide the wavelengths needed for photosynthesis and can compensate for the lack of natural light.
3. Keep a close eye on your plants. If you notice that they are showing signs of distress, such as yellowing leaves or stunted growth, you may need to adjust their lighting environment.
4. Place indoor plants outside during the summer. This can help them get more natural (and UV) light, which is beneficial for their growth. However, it’s important to acclimatize them gradually to avoid shock. Start by placing them in partial shade, then gradually increase their exposure to direct sunlight. Be sure to monitor weather conditions and water regularly to avoid water stress.

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Larry Hodgson published thousands of articles and 65 books over the course of his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This text was originally published in Le Soleil on July 10, 2024.