Chitosan derivatives with low molecular weight can enhance plant growth and improve tolerance to various stress. Hardy ferns form a group of attractive garden perennials with unknown response to plant biostimulants. Cold winter temperature limits the growth and reduces the decorative value of evergreen fern species. This study was carried out to explore the effects of chitosan oligosaccharide lactate (COL) with Mn = 5,000 on growth of evergreen fern Cyrtomium fortunei var. clivicola. COL sprayed at 50 and 100 mg/L significantly increased height of plant and fresh weight of the above-ground and the underground parts of C. fortunei var. clivicola compared to control plants. Moreover, ferns sprayed with 50 and 100 mg/L COL also had higher leaf total chlorophyll contents and value score. These results indicate that COL improved C. fortunei var. clivicola growth and overwintering and may be used for high quality hardy ferns production.