Tithonia diversifolia is often grown as a cover crop or as a green manure crop in climate smart agriculture practices. This plant can be harvest at various growth stages, and the biomass can be incorporated into the soil. The decomposition of plant biomass enhances the soil nutrient, organic matter content and crop productivity. This study aimed to determine the best harvesting stage of T. diversifolia to be used as an efficient soil amendment for coconut plantations. Samples were collected at one, two, three, four, and five months of harvesting stages from an existing T.diversifolia field at Rathmalagara Research Station of the Coconut Research Institute of Sri Lanka. In the study, both plant growth parameters and nutrient composition of each plant part were individually evaluated for every section of the plant. Biochar was prepared from hardwood stems of T.diversifolia using them as the feedstock under five different temperatures 300 ᵒC to 700 ᵒC, and a proximate analysis was done for the characterization of produced biochar. The mean values of measured parameters of T. diversifolia and the properties of biochar were significantly different (P<0.05) at different growth stages and temperatures, respectively. Considering all the measured parameters of T. diversifolia, three months harvesting stage can be suggested as the best growth stage to be used as green manure. According to the proximate analysis results and by observing the half-burning of produced biochar, 500 ᵒC can be proposed as the ideal temperature to produce biochar from hardwood stems.