The 'low chill' controversy
Has anyone clearly observed what symptoms appear as a result of low chill? I've read multiple reports on this, but I've never had the opportunity to observe for myself.
What I've heard so far is:
1) Delayed blooming
- I think applenut has reported that some of his so-called high chill apples simply bloom a lot later and therefore fruit a lot later, which doesn't seem to be a big problem.
2) Reduced blooming, or blooming over a longer period of time.
- I've heard about this showing up on cherry trees, leaves come out first, and blooms follow, but less and over a longer period of time.
3) Significant reduction in vigor
- One of our local CRFG members lives right on the coast and he has observed that a number of higher chill apple trees will grow much less vigorously on the Winter sunny side of the tree (south side).
i don't think this chill thing is really well understood. For one, I've noticed that a rather large number of so-called low chill apples and even low chill cherries happen to be self-fertile and early bearing. Pettingill, beverly Hills and Gordon are apple trees that come to mind, and lapins and Stella are a couple more. Are these really "low chill" or are they just self-fertile.
Now there are real low chill fruit trees: Anna and Dorsett Golden apples are not self pollinating, but they will produce up to three crops a year in mild climates and seem oblivious to the seasons. The new Royal Lee and Mini lee cherries from Zeigers will bloom and fruit when spurred by manual defoliation after a zero-chiil Socal Winter.
Now I happen to be in a medium chill area, (800h on average) but fairly freeze free. My first attempt at growing Dorsett Golden doesn't suggest it's capable of doing three crops here. it's bare right now, although it seems to be getting ready to bloom.
My basic understanding of chill is that the higher chill requirements simply keep a tree dormant through occasional Winter warm spells, or by requiring a longer early Springtime chill exposure. If it's below freezing, apples don't accumulate any chill. So most of the chill accumulated in Northern latitiudes takes place either during the late Fall or early Spring.
So the questions I have are:
- How often does it turn out that chill accumulation is erroneously attributed to poor fruiting when in reality the issue is either pollination or fruit tree maturity?
- How many "chill ratings" do nurseries pull out of thin air simply by looking at where a fruit originates from? The typical erroneous logic goes something like this: "German, Canadian and Upper-Midwest originating apples must be high chill because they come from places that have high chill."