Plant factors (PF) are expressed as a percentage of which water component?

• A. Soil Moisture
• B. Precipitation
• C. Evapotranspiration (ETo)
• D. Groundwater Levels

Answer: (C)

Plant factors (PF) are specifically expressed as a percentage of potential evapotranspiration, more commonly referred to as evapotranspiration (ETo). This metric represents the amount of water that would be evaporated and transpired by plants if sufficient water were available in the soil. Understanding PF in relation to ETo allows landscape professionals to make informed decisions about irrigation practices, ensuring that water is applied efficiently to meet the plants' needs without excessive runoff or waste.

Using ETo as a baseline is critical because it accounts for variables such as temperature, humidity, wind speed, and solar radiation, which all influence the rate of water loss from the landscape. By determining how much water a specific plant type requires in relation to ETo, landscapers can establish appropriate irrigation schedules and optimize water use in their designs.

In contrast, the other options, such as soil moisture, precipitation, and groundwater levels, while important components of the water cycle and local hydrology, do not serve as the primary benchmark for the expression of plant factors. They play supporting roles in overall water management and plant health but are not the standard against which plant water needs are quantified in the context of PF.