I’ll start off by giving the stats for my immediate area as of Dec 31.
Below 45 Model: 163 chill hours
Between 45 and 32 Model: 144 chill hours
Utah Model: ** -208** chill units
Positive Utah Model: 315 chill units
Dynamic Model: 7 chill portions
I checked out other nearby stations and had comparable results. When I first started checking these numbers on Tuesday, I believe that I took from them what I wanted - a bit of security to bolster my desire for my fruit trees to get through the winter unharmed and to provide a decent harvest next year. I interpreted the #s as showing that we’ve had insufficient chill hours for our periods of winter warmth to propel them toward prematurely breaking dormancy.
My first fruit tree blooms have always been on my Japanese plums, followed by cherries which overlap peaches and the earliest blooming apples. I’ve been closely examining those plums and cherries each day and they seem to be sleeping peacefully. I do continue to convince myself that any slight fattening I might perceive on the cherries is only my imagination.
I’ve been checking the apples now and then out of curiosity over when and if some of them were ever going to go into total dormancy. If it’s true that chill hours don’t count until all the leaves have fallen, then those that hadn’t completed, or in some cases even begun, the process of shedding them would still have zero hours.
I do not enjoy cold weather. To me “cold” is when nights are in the 30’s or below and days are less than 65F for highs. However, since my understanding is that the fruit trees need that weather, I’ll welcome it for their sake.
That’s the way I’ve been thinking up until Wednesday when I went to check the apples to see how far along the established ones were toward losing their leaves. Now I’ve got a glimmer of one reason people keep creating different ways of calculating chill. I’m also disheartened over an increased likelihood that I may once again harvest zero apples this year.
My earliest blooming apple is a Double Red Delicious. So far, I haven’t had any other varieties overlap its bloom. So, of course, I’ve never gotten any fruit from it. My understanding is that Red Delicious varieties require between 700 and 800 chill hours. Wednesday I noticed that some of what I’ve been sure are fruit spurs had wee tips of green showing. Today those tips have become mouse ears and I can see that, yes, they are bud clusters. Those branches have leaves popping out all over them now. Some other branches are a few days behind.
My other youngish established apples appear to be following behind that one at about the same rate of development as last year. However, we are about to leave this protracted warm “fall” behind and enter a period of days in the 50’s and 60’s and nights in the 30’s and 40’s. There are still two months of winter to go. I suspect that at least this one tree may wind up damaged during that time.
As much as I’m apprehensive about the apple trees’ performance over the year, it’s also been interesting observing the performance of all the trees and food producing plants during this year of extremes and anomalies. I suspect that chill hours may be less of a factor in determining when apples and berries push out new growth and blooms than it is with stone fruits. We had a wet spring, followed by a long, hot summer with few rains, and a very warm autumn interspersed with short periods of chill on approximately a bi-weekly basis for the past 6 weeks while the ground has been alternating between flooded and just plain wet since the last week of September. Fruit trees here start losing leaves during the summer heat. They don’t really put on growth in summer, but the apples do put out new growth in fall. For the established apple trees that still retain some leaves, it’s that autumn growth that is still holding on to them.
In answer to Bear’s question of whether chill requirements have been met yet - I don’t know. I suspect that chill hours don’t stand alone, that the determination of whether they’ve been met operates in conjunction with other factors such as day length and whether it is increasing or decreasing, moisture, nutrition, past and current stresses and relief from those stresses, and the number of growing degree days since the last period of growth. I also suspect that the significance of any combination of factors differs from one variety of fruiting plant to another.
The thoughts I’ve shared are intuitive based on observation and extrapolating from others anecdotes, not on controlled studies. I’m just surmising from my very limited knowledge and experience. There are others here who have much much more of both than I do. I hope they speak up and right the course of my thinking if it is off track.