Polyethylene mulches with black or white surface were compared in seven strawberry (Fragaria × ananassa Duch.) genotypes in a 2-yr experiment. The plants were covered by an unheated walk-in tunnel at the beginning of the first harvest season. The effects of a south-west versus north-east position of plants within the double-row beds were also studied. Soil temperatures were higher under black mulch, especially mid-day temperatures on the bed surface in the southward position. White mulch favoured root and crown growth in the first year, and the southwest position increased plant growth in both years. With black mulch, lower carbohydrate reserves were observed after transplanting, and a decreased chlorophyll content of leaves was detected in the second year. Mulch colour did not affect yield quantity. The first-year harvest was advanced with black mulch, but in the second year, the harvest season was earliest on the south side of beds with white mulch. Black mulch decreased fruit size in the first year and the concentration of fruit soluble solids in both years. The results suggest that in northern latitudes white mulch improves strawberry plant growth and fruit quality over that obtained using black mulch, but enhanced yield is not to be expected when a double-row tunnel cultivation system is used. Key words: Fragaria × ananassa, mulch, plasticulture, polyethylene, strawberry, tunnel