The relevance of developing construction composites based on polymer waste and non-wood plant fillers is highlighted in the study. Analysis reveals that non-wood plant waste can effectively serve as fillers for construction composites based on secondary polyolefins. It is observed that the main strength and performance properties of filled composites depend on the structure and physicochemical interactions at the phase interface, as well as on the surface properties of filler particles. The addition of plant fillers of different chemical nature to polyolefin composites enhances their physico-mechanical properties. Regulating the quantity of each plant filler in the composite allows for obtaining compositions with a combination of improved physico-mechanical and performance indicators. Mathematical dependencies of the physico-mechanical and performance characteristics of plant-polymer composites (PPCs) on the ratio of each component in the composites are investigated. Regression response surfaces, derived from the obtained regression equations, provide visual representation of the corresponding geometric image. Through mathematical processing of the experimental data, polynomial dependencies (regression equations) reflecting the influence of qualitative and quantitative composition on the properties of composites are found, and optimal compositions with better strength and performance indicators are identified.