Plants get their energy for metabolism from cellular respiration, which consumes oxygen and releases carbon dioxide. They do this 24-7. During the day, photosynthesis, which creates the carbohydrates that are fed into the cellular respiration cycles, consumes CO2 and releases a considerable amount of O2.
These are two separate processes. The upshot is that during the day, a plant has a net release of O2 and during the night it has a net consumption of O2.
But the volume of this gas exchange is so small, and the proportion of O2 in the ambient air so large, that oxygen depletion is only measurable very close to the surface of the leaves, as diffusion of oxygen from the surrounding atmosphere replaces that consumed by the plant.
In case of multiple fully grown tree nearby could lead to oxygen depletion, hence our elders avoid sleeping under a tree.
One reason to avoid trees at night would be because you cannot fully see the condition of the trees including branches that may fall or trip you up. In addition, being around trees in a storm (at night) is not a good idea because of the lightning danger.
In addition, at night you may not be able to see dangerous, spiders, bugs, or snakes that make their home in trees.
In addition, at night it is difficult to identify dangerous plants (e.g. poison ivy, poison oak, stinging nettle, etc.). Anyone that has played a game at night and accidentally run into a patch of poison ivy understands this.
Hence keeping house plant indoors or in garden cause no harm.
Houseplants do more than just beautify your indoor space. Research shows that keeping plants inside your home can bring a host of physical and mental health benefits.
Once you learn more about the therapeutic nature of plants, you’ll be inspired to get your green thumb on.