I think most of the fruit trees and blueberries in Mississippi have enough chill hours, but with the warmer temperatures we've had, it's marginal this year. Much of the problem comes from planting species not native to the area. A plant from the Coast requires fewer chill hours than does one native to more northern areas. A southern plant growing away from its native area may accumulate enough chill hours to bloom in January or February rather than in March and April when it should. If the weather turns cold again, that plant will suffer.
Hormones control when the plant goes dormant and when it grows.
The number of chill hours needed by native plants in the state ranges from 400 to 1,400, Rasberry said. If you take something that belongs somewhere else, it may or may not be able to adjust to the climate. While nothing can be done for those plants that have already bloomed early or are caught by a late freeze, commercial growers have access to Dormex, a plant growth regulator. It tricks plants into blooming and putting on leaves by adding 100 to 200 chill hours. When used correctly, Dormex is a very safe substance that leaves no residue on the plants and breaks down into fertilizer.