So, what is plant transpiration?

Plant transpiration is the process where moisture is carried through plants from roots to small pores on the underside of leaves has it changes to water vapor and released back into the atmosphere. Plant transpiration is really evaporation of water from plant leaves. It’s the way plants perspires.
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Transpiration and plant leaves

Plants grow roots down into the soil to draw water and nutrients up into the plant stems and leaves. Some of this water is returned to the atmosphere by transpiration. The amount of transpiration varies widely depending on weather conditions, such as temperature, humidity, sunlight, precipitation, and soil type.

How much water do plants transpire?

Plant transpiration is an invisible process, since the water is evaporating from the leaf surfaces you can not see the leaves “sweating”. Even though it’s not noticed, during the growing stage, a leaf will transpire many times more water than its own weight. For instance, an acre of corn gives off about 3,000-4,000 gallons of water each day, and a large oak tree can transpire 40,000 gallons per year.

What does transpiration mean for aeroponic growers? It means every square foot of aeroponics growing has the potential to transpire 1 1/3 cups of water per day. However, for most crops grown indoors it more like 1/4 to 1/3 cup of water per day per square foot.

As the temperature climbs so does the transpiration:

Transpiration rates go up as the temperature goes up, especially during the growing season, when the air is warmer due to stronger sunlight and warmer air masses. Higher temperatures cause the plant cells which control the openings (stoma) where water is released to the atmosphere to open, whereas colder temperatures cause the openings to close.

As the humidity climbs, transpiration drops:

As the relative humidity of the air surrounding the plant rises the transpiration rate falls. It is easier for water to evaporate into dryer air than into more saturated air. As plant growth progresses in an aeroponics system, the humidity will rise. Therefore, the transpiration will slow down. So the plant requires less misting of the roots.

More air movement increases transpiration:

Increased movement of the air around a plant will result in a higher transpiration rate. This is somewhat related to the relative humidity of the air. As water transpires from a plant leaf, the water saturates the air surrounding the leaf. If there is no wind, the air around the leaf may not move very much, raising the humidity of the air around the leaf. With some wind movement, the more saturated air close to the leaf is blown away and replaced with drier air, thus increasing more transpiration.

Dry roots drastically drops transpiration:

When moisture is lacking in the root zone of an aeroponics system, plants begin to senesce. This is like premature ageing, which can result in leaf loss. Sick or no leaves on the plant leads to less or no transpiration, sadly the death of your plant.