Is there a safe rule-of-thumb one can apply to determine how low the temperature can go without causing severe damage to a plant? The USDA plant hardiness zones are useful as a starting point. However it may not be good enough for certain plants. Case in point. Murraya paniculata is rated as a zone 10-12 which suggests it would survive to -1C. This contradicts warnings that the plant would be killed by temperatures below ~12C -- much higher than zone 10 minimum. Contrast with Aglaia odorata which is also rated a zone 10-12 but its minimum temperature is ~2C which is much closer to the zone minimum. So how can one be sure? Of course the proper way is to research each plant individually. However cultivation requirements for some plants, particularly lesser known tropicals, are hard to come by and the trial and error method could result in dead plants. Any help?