Faced with increasingly constraining herbicide regulations, many land-managers are turning towards alternative methods to control highly invasive plants. For clonal plants such as Japanese knotweed s.l. (Reynoutria spp.), “tarping” (a.k.a. covering) is frequently applied yet with contrasting results, as robust recommendations regarding effective application are currently lacking. We used a survey-based dataset of tarping operations in Europe and North America to explore the factors affecting the success of knotweed control by tarping. Variations of four response variables were analysed: an effectiveness score (estimating the capacity of tarping to limit the vigour, lateral spread and propagule dispersal of knotweed stands), the visual eradication status of the plant, and the presence of knotweed regrowth at the edge of the tarped area or at the junction of fabric strips. Among 85 evaluated operations, 59% had high effectiveness scores (> 0.75) and 27% reported a complete visual eradication, suggesting that some tarping implementations can be very effective against knotweeds. Tarping effectiveness significantly decreased with increasing proportion of obstacles and for partially covered knotweed stands. Moreover, covering knotweeds entirely and increasing the covering distance beyond the stand edges strongly increased the probability of visual eradication. Increasing this distance and digging surrounding trenches decreased the likelihood of finding regrowth at the edge while levelling the ground decreased that of finding regrowth at the junction of strips. Our results suggest that tarping can effectively control knotweed populations provided careful planning and execution. However, we strongly advocate that tarping should be best viewed as a transitional step in a restoration process.