How to Measure Transpiration in a Cactus

Fill a pot similar to the one the cactus is growing in with soil that is as similar as possible to the one the plant is growing in. Duplicate as closely as possible the amount of soil and type of pot to more accurately measure the transpiration rate. Ideally, use the exact same type of pot with the exact same amount and type of soil.

Cut out a plastic circle that covers the same amount of soil on the surface of the pot as the cactus plant in its pot. This is your control pot. To calculate the transpiration rate of a cactus plant by weight you must control for the water weight lost through evaporation from the soil surface.

Fill a graduated cylinder with water. When the cactus is dry and needs watered, measure the amount of water used exactly. Add the same amount of water to the soil evaporation pot.

Weigh your potted cactus plant and record the amount. Weigh the evaporation control pot and record the amount.

Place the two pots in the same location. Expose both pots to exactly the same environmental conditions such as sunlight, wind and temperature.

Weigh the two pots at the same time every day for a week. Record the weights. Subtract the amount of weight lost from the control pot from the weight lost from the cactus plant pot to calculate the amount of transpiration from the cactus plant. For example, if the control pot lost 3 oz. in a day and the cactus plant pot lost 7 oz., the amount transpired by the cactus plant is 4 oz. of water.