Popillia japonica Newman (Coleoptera: Scarabaeidae) is a priority quarantine pest of the European Union that can pose an economic threat to certain agricultural activities. When female beetles have a choice, container substrates are not the preferred or suitable oviposition sites; however, plant nurseries are a potential pathway for spreading the pest. For this reason, producers must abide by restrictive measures to guarantee P. japonica-free plants, leading to major restrictions on their commercial activities. An innovative and sustainable approach to P. japonica control involves the application of a mulch layer to potted plants to physically prevent beetle oviposition. A choice test compared the effectiveness of 13 mulching materials in preventing P. japonica oviposition and the influence of soil moisture on egg laying. Additionally, for 10 of these materials, the role of mulch physical properties in preventing oviposition in potted plants was assessed in a no-choice test. The survey demonstrated that mulching can significantly reduce the risk of P. japonica’s oviposition in container substrates. Mulches with higher specific weights, such as gravel and lapilli pebbles, achieved greater control. Soil moisture influenced P. japonica oviposition, with higher moisture levels leading to increased egg laying. The application of suitable mulches represents an effective phytosanitary measure to improve the sustainable management of P. japonica in nurseries.