Horticultural produce is stored in corrugated boxes in coolrooms under high and variable humidity conditions. As the boxes are stacked up, they experience compressive loads under which they creep and buckle and may fail. In the present work, citric acid was used for covalent crosslinking of linerboard and the outer linerboards of corrugated boxes. Crosslinking involved esterification of cellulosic hydroxyl groups by citric acid and was effected at a high temperature without a catalyst. Part of the citric acid was degraded during curing via thermolytic reactions. The treatments resulted in a significant improvement in linerboard short-span compressive (SCT) strength, which increased with an increase in curing temperature and citric acid dose. Most of the ester linkages were stable under prolonged storage of the boards at high humidity. In the case of corrugated boxes, a greater than three-fold increase in resistance to compressive creep was achieved. The improved box properties may extend the lifetime of corrugated boxes under the conditions used for storage of horticultural produce. A remaining challenge is to achieve sufficient thermal curing on a modern high-speed corrugating line.