Mulching is a common soil management technique used in agricultural, nursery, and landscape settings. Despite multiple benefits, such as reducing weeds and evaporation, some mulches can also hinder gas exchange across the soil-atmosphere interface, and thus may have negative impacts on plant growth. The objective of this study was to determine to what degree commonly used landscape mulches will affect carbon dioxide and oxygen concentrations in the root zone and gas exchange across the soil-atmosphere interface in a controlled greenhouse environment. We used mesocosms filled with a soil-compost mix and covered the surface with different mulches. The experimental treatments included no mulch (control), arborist wood chip mulch, cardboard mulch, landscape fabric mulch, and polyethylene film mulch. The flux of CO2 across the soil-atmosphere boundary was measured with the dynamic closed chamber method. Concentrations of CO2 and O2 were measured in the mesocosms at two depths (6.5 and 13.5 cm) for a total of 16 days after covering the mesocosms with the mulches. Diffusion coefficients of CO2 through mulch materials were of the order of>10−3, 10−4, 10−5, and
10−6 cm2 s−1 for wood chips, cardboard, landscape fabric, and polyethylene film, respectively. Despite the different diffusion coefficients of the different mulches, CO2 and O2 concentrations in the soil under the various mulches were not significantly different as compared to the control, except for the polyethylene treatment. The orders of magnitude differences in diffusion coefficients among the mulch materials, however, could negatively impact a diverse soil environment such as those found in biologically rich landscapes with higher oxygen demands. Among the mulches tested, wood chips are a preferred method of mulching in terms of providing best gas permeability, particularly in landscape conditions.