Using cardboard underneath mulch is an effective weed-suppression technique for rose beds, working as a physical barrier that blocks light and prevents seed germination [1][2][3]. The cardboard gradually decomposes, adding organic matter to the soil over time [1][4][2].

To install cardboard successfully around roses, use plain, brown corrugated cardboard and remove all tape, labels, staples, and plastic-coated sections [2][5]. Lay pieces so they overlap by 6–8 inches to prevent light gaps, and soak the cardboard thoroughly with water before and after installation to encourage decomposition and water penetration [1][2]. Cut small holes or X-shapes where each rose stem is located, keeping the cardboard at or below soil level and leaving a gap of several inches around the crown and base to prevent moisture buildup and rot [2]. Cover the cardboard with 3–4 inches of organic mulch such as wood chips, bark, or shredded leaves, avoiding piling mulch directly against the rose stem [1][2].

Before laying cardboard, remove or cut back existing weeds, especially deep-rooted perennials and runners, so they cannot push through gaps or around edges [2]. Cardboard can modestly reduce water and air movement at the soil surface, but when kept moist and covered with adequate mulch, it generally allows sufficient water infiltration and oxygen diffusion as it breaks down [1][2].

Cardboard is less suitable in very dry climates or poorly draining soils, where it may prevent rainfall from reaching roots or prolong surface wetness and anaerobic conditions; in those situations, use a thick layer of loose organic mulch alone instead [1][2]. Cardboard typically lasts 6–18 months depending on temperature, moisture, and soil biology, making it a temporary rather than permanent barrier; you can add another layer later if needed [2].