In a covering material comprising a base material containing a colorant, the type and content of the colorant are chosen to provide a photosynthetically effective photon flux (PPF) transmittance of 50% or greater when light is passed through the covering material, and an A value suitable for the purpose of promoting or retarding the growth of plants irradiated with light transmitted by the covering material, the A value being defined by the following equation: where R is the photon flux of red light in the wavelength range of 600 to 700 nm and Fr is the photon flux of far red light in the wavelength range of 700 to 800 nm.