Plants are highly evolved in their own way to be able to grow, and even thrive, using just a few vital necessities, including nutrients, water and sunlight. Like humans, no land-based plant can survive long without water. Plants also can't grow without sunlight, which they harvest to make the chemical energy that powers their life processes. Plants that don't get water and sunlight eventually die of dehydration and energy loss.
Plants need a lot of water. Actually, plants use more water than humans and animals do. Plants themselves are about 90 per cent water, while animals (and humans) can be as little as 75 per cent. Plants also make direct use of water when sunlight falls upon them as a part of their photosynthetic energy-generating life process. Plants exchange water for the carbon dioxide they breathe in (called "transpiration"), meaning they need to replenish their water supply frequently.
Sunlight is the most vital necessity when it comes to plant growth. A plant could be given all the water and nutrients in the world but it would be of no use without sunlight. Through photosynthesis, a plant harvests light that falls on its leaves and even its stems and branches and converts it to the energy it needs to grow. Plants have finely developed cells known as photoreceptors that help them harvest the right colours of light contained within visible light.
As soon as sunlight, or the right kind of artificial light, stops falling on a plant, its photosynthetic processes stop immediately. Most plants outside of trees if deprived of the sunlight will die in a few weeks. Small seedlings will die after only a few days to a week in the dark. Deciduous trees and shrubs (they lose their leaves on an annual basis) can last from six months to a year without sunlight, but once their energy reserves are exhausted, they'll die, too.
How much water a plant needs to grow and survive depends on what type of plant it is, how old it is and how much light it gets. Mature houseplants need to replace their body weight in water every day. Bamboo plants, for example, require daily watering in hot or windy weather and will die quickly if they don't get it. Likewise, most houseplants need watering on a daily to weekly basis. However, some succulent plants such as desert cacti can go years without water.
When it comes to light, plants require anywhere from 10 to 16 hours of it to fully power their photosynthesis. It's always best to give plants a little water and a little light every day. How long a plant can last without water varies by species. Some plants will die a few days after water is stopped, while certain desert cacti can live for years without water.
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- Michigan State University; Why Do My Plants Need So Much Water?; Sept. 21, 1994
- PopSci; If the Sun Went Out, How Long...Survive?; Holly Otterbein; Oct. 20, 2008
- The Guardian; How Long Can Someone Survive Without Water?; Kate Ravilious; Dec. 3, 2005
- University of Clemson Cooperative Extension: Why Plants Need Water
- LiveScience; How Cacti Survive: Surprising...Thirst; Corey Binns; July 23, 2006
- Fulton-Montgomercy Community College: Photosynthesis