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Biochar is a valuable soil amendment and is recognized to have a positive effect on the crop yield, soil quality, nutrient cycling, and carbon sequestration. However, the effect depends on biochar characteristics, doses, and soil properties. This paper reports the study on determination of the effect of different rates of biochar based on their size fractions on water retention characteristic of sand-based rootzone mixture characteristic for natural turfgrass rootzone. The pot experiment was established using a soil with the texture of loamy sand. Mixtures of biochar and soil were prepared in March 2014. Biochar was produced using the straw of two species, namely miscanthus and winter wheat, by pyrolysis process at a temperature of 300 °C for 15 min with limited air access. Then, biochar particles were separated into three size fractions as follows: 0–500 μm, 500–1000 μm, and 1000–2000 μm. The following four biochar rates were used in this experiment: 0.5%, 1%, 2%, and 4%. The results indicated that biochar application significantly improved the physical properties of the tested sandy soil. The basic soil physical parameters, such as bulk density and total porosity, were not only dependent on the rate but also on the size of the biochar. Small particles of biochar reduced the volume of soil pores in diameter below 0.5 μm but increased the volume of larger pores with a diameter 0.5–500 μm. Biochar application increased the available water content (AWC), especially when the finest fraction was used (0.064 cm 3 cm − 3 ). Biochar made of miscanthus was characterized by higher AWC (0.056 cm 3 cm − 3 ) than that made of winter wheat (0.050 cm 3 cm − 3 ). In the present study, the soil water repellency was increased by biochar application, but it was still classified as non-repellent. [ABSTRACT FROM AUTHOR]