Flowering of rhubarb (Rheum spp.) was affected by plant age and vernalization temperature and by vernalization time in young crowns. Year-old crowns flowered after storage at 0°C or 5°C for 3 months or more. All 19 week-old crowns flowered after storage at 0°C for 3 months or more and some flowered after storage at 5°C. The 16 week-old crowns flowered only after 4½ and 6 months storage at 0°C. None of the 13 week-old crowns flowered. There was no flowering of crowns stored at 10°C regardless of age or length of storage. Growing temperature and photoperiod following vernalization did not influence flowering.