The blackberry model accumulates 1 chill unit when temperature is between 0 and 7° C. Chilling inception occurs at the first incidence of -2.2° C (28F). This last part, the inception date, I believe it the primary problem of the model. This temperature did not occur until December 29, 2011, more than 3 weeks later than the year before (12/06/10).
I am not sure that the blackberry model is valid in assuming the inception date based on a minimum temperature trigger. Other models start on a certain date or in the case of blueberry, once the positive balance is not negated by warm weather (see model definition and link below). Based on the blueberry model, we have accumulated 1055 chilling hours at the same location.
Which one is best? I don't know, I hope we will accumulate more chilling this month. My instincts say that we should be fine and that the plants have accumulated more than the blackberry model has determined. And... we are taking bud break data and will be watching growth this summer.
The blackberry chilling model posted at
Blackberry Model accumulates 1 chill unit when temperature is between 0 and 7° C. Chilling inception occurs at the first incidence of -2.2° C.
Warmund, Michele R., and J. Krumme, "A Chilling Model to Estimate Rest Completion of Erect Blackberries," HortScience 40(5):1259-1262. 2005.
I will be following the blueberry model as well,
Blueberry Model accumulates 1 point for average hourly temperatures below 45° F; 0.5 point for temperatures 45-55° F; -0.25 point from 55-65° F; -1 point for temperatures 65° F and above. The model begins when it has a positive balance that is not negated by warmer weather. Once 800+ chill hours have accumulated, points are no longer negated for temperatures 55° and above. The model ends February 28 at midnight.