"Late season cold tolerance is totally different from early season cold tolerance or mid season cold tolerance."
This is exactly what I have observed but it is the first time I've seen it discussed. The genetic complexity is pretty boggling.
It's been very noticeable, that the seedlings that wimp out in early cold and maybe suffer some foliage disease too, may still turn out to be great performers in the late fall (Danko is one standout example).
One thing I've noticed, that purpling of the leaves .(indicating phosphorus deficiency due to cold) is absent or reduced in cold-exposed seedlings of a couple of varieties that seemed to have pretty good cold tolerance throughout the season (Al Kuffa, Black Early and Indian Stripe are the ones I'm thinking of from last year). Then you have others that purple dramatically in the cold - Rozoviy Flamingo heart for example - but hang on into the fall without disease,happily purple, and set and quickly grow fruit in low temperatures when others have given up.... it's very confusing.
