Equipment for testing root cold hardiness of containerized forest tree seedlings is described in the paper. Using this equipment roots of containerized one‐year‐old Norway spruce seedlings were experimentally frozen on December 3. After freezing, lateral roots were divided and cut into young and mature parts. Samples of young and mature roots were then tested for vitality using the triphenyl tetrazolium chloride (TTC) method. In contrast to mature roots, the reduction of TTC decreased as younger roots were exposed to the lowest test temperatures of — 15°C and —20°C, indicating increasing root damage.