The complex relative permittivity of a plant is a function of its contained amount of water, solutes (mainly their salinity) and temperature in all plant compartments (including roots). The more water and the higher the salinity are in the plant compartments, the higher is the complex relative permittivity of the plant. The complex relative permittivity of a plant refers to the complex relative dielectric constant of the plant and can be subdivided into complex relative permittivity values for the different plant compartments (roots, stem/stalk, leaves, fruit,...). The complex relative dielectric constant or permittivity parameter has a real and an imaginary part indicating the moisture content and the conductivity (loss) of the plant medium. Models of plant permittivity consist mostly of a free-water and a bound-water part. In particular, plant water is a solute of nutrients and not all water-conducting plant cells are fully filled by water, but also with air. Hence, the estimation of one plant permittivity, especially including several plant parts can be challenging to assess, to understand and to model. To acknowledge this mixture of components, dielectric mixing models containing the single material components are normally developed and applied, representing an effective complex relative permittivity of all plant components. Concerning a vegetation canopy, electromagnetic waves interact with a more or less sparsely vegetation-filled volume unit of air. A vegetation canopy represents a dielectric mixture of vegetation inclusions (leaves, twigs, branches, stems,…) distributed in a volume of air. Dielectric mixing models of canopies take this vegetation volume fraction into account.