Why does my plant need water?

August 1, 2015

All living things need water to stay alive. However plants need more water than most living things because they use more water than most living things. The amount of water your plant needs to thrive is dependent on 3 things: what type of plant is it, how much light it receives, and how old it is – but how it utilizes that water is the same.

Two Fundamental Ways Plants Utilize Water

1. Turgor Pressure

Turgor pressure is the pressure that pushes the plasma membrane against the cell wall of a plant. The plasma membrane is the membrane that separates the interior of all cells from their outside environment. This pressure, turgidity, is caused by the osmotic flow of water from outside the cells into the cells, i.e. the water flows through a cell’s membrane to go from an area of low concentration to an area of higher concentration.

Healthy, or well-hydrated, plants are considered turgid – or expanded/blown up by fluid (water). This helps them maintain their structure, and not wilt. Hence wilting is a common sign of under-watering for most houseplants.

2. Photosynthesis (& Transpiration)  

Water is vital to conducting photosynthesis, too. Through a plant’s stem, water enters and travels up to its leaves where photosynthesis takes place. The water evaporates in the leaves as the plant exchanges it for carbon dioxide. This is called transpiration and takes place through tiny openings, like plant pores, called stomata (plural of stoma). Plants use the carbon dioxide to make food. They do this by combining carbon dioxide with water to create sugar. This action is possible thanks to the energy they receive from the sunlight. So it is no surprise that for most common houseplants, transpiration occurs during the day when there is natural light.

– Hence the common phrase ‘morning dew’ can be explained by photosynthesis and transpiration. Because most plants need sunlight (and the energy it provides them) to exchange water for carbon dioxide – the water that plants pull into their leaves at night does not evaporate through their stomata, and instead remains on the leaves as dew.

– When transpiration does occur during daylight, it also cools down your plant in the same way that us humans sweat to cool off.

– A mature house plant can transpire its body weight daily! That’s a lot of water. If people needed that much water – an adult would have to drink around 20 gallons of water daily.

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