Chilling in my greenhouse, messed up again!!
Ran chilling cycle 56 days this year and wrote down high and low temperature each day. The extremes in 56 days were 63 and 34F. Average high and low 54/37F. These are almost exactly the averages in the best fruit growing areas of CA for Dec and Jan in say Modesto where Zaiger resides. What more could you want, right?
According to Texas A&M the Utah model allocates 1.0 units chilling per hour to any temperature between 37 and 48F. Based on that over the years I've been estimating 14-18 units, hours, chilling per day. 56 days x 16 hours/day = 896 hours chilling.
But the left side of figure 4 in the link below shows a very sharp peak in chilling effectiveness at 40F. At 37 and 48F chilling is only about 60% as effective as at 40F. Using this I'm maybe looking at 10-12 hours chilling per day at best. That's 560 to 672 hrs chilling this year.
Based on my trees reaction 600 hrs is probably more accurate. The sweet cherries and higher chilling apricots are not going to set more than 5-10% crop again this year.
Next years it's 90 days all out chilling or bust!!!!
Here is a link that might be useful: Check left side fig 4: utah hr vs temperature