Lignin formulations for making light-selective mulch, methods of making such lignin formulations, light-selective mulches comprising substrates treated with lignin formulations, and methods of making such light-selective mulches. Some methods involve preparing aqueous lignin formulations that can be used as coatings that, in turn, can be applied to a substrate, such as a paper web, to form a biodegradable, light-selective mulch. Some such mulches blocks at least some light in the ultraviolet and blue/green ranges (350 nm to 500 nm) of the visible light spectrum to inhibit weed growth below the mulch, while also transmitting light in the red/infrared ranges to heat the soil below the mulch.