Lower chill blueberries for changing northern climate?

I’m in southern NH, Z5b. Our winters, like so many, are getting shorter, with more (and more extreme) freeze/thaw cycles in the spring. We saw a few 80+ degree days in early April this year, followed by a 6-hour 24 degree spell one mid-late May night! Obviously very bad for early bloomers…apricots, peaches and the like, and this year, even for apples.

I’ve heard rumors (NPR, I think) that many of the commonly grown northern highbush blueberries may no longer receive the chilling hours they require, and I’m wondering what the best approach is, in terms of hedging one’s bets against total loss. I’m a backyard grower/orchardist and have room for more plants – just looking for a bit of guidance as we head into even warmer/more inconsistent spring weather.

Does it make sense to plant some Z5-hardy southern highbush varieties, and if so, should I be looking only at plants that have relatively high chill requirements (that is, for southern highbush)? 400-500 hours (O’Neal, Jubilee), say, versus 150 (Sunshine)? (All my current plants require 800-1200 hours.) My fear is that the lower in chill hours I go, the earlier the plants will break dormancy, and the higher the danger of cold injury will be (but then again, perhaps plants that are adapted to a warmer winter will be less likely to break dormancy in the event of unseasonably warm spells in midwinter, which are likely going to become more common here…) – I feel there must be a sweet spot…but where is it?

Can anyone tell me if this makes sense – am I thinking of this problem clearly? Any thoughts on how to proceed, in future plantings? And do any of you Z5 growers have experience with lower-chill blueberries?

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Erratic spring weather requires chilling hours at least as high as the amount of hours nature is giving. Are your current blueberries blooming too soon? If so, it is because they don’t have high enough chill requirement and/or heat requirement in spring is too low.

Breaking dormancy has two requirements, first enough chill hours to satisfy the plant’s built in requirement, second enough heat to induce breaking dormancy. Current varieties are rated for chill hours but not heat requirements.


I have tried southerns here in 6a with terrible results. Remember the warming is only fractions of a degree over decades. In 2075 you may be able to grow them. There are some hybrids you could grow there now. Like Legacy or Nocturne. Why don’t you start with these which can grow in both environments. That makes sense. They are both excellent tasting. Nocturne Berries go from red to almost black. Darkest berry I have seen. Beautiful!
Legacy has a fine complex flavor that improves as bush matures. Both flower very late for southerns. If you go with traditional southerns the first warm spell they will break dormancy and could be damaged by further cold. Mine eventually died from breaking dormancy to early for my zone. Stick with late bloomers, chill hours are so low in most southerns they are ready as soon as any warm air hits and will grow too early. Mine eventually died of cold damage. Legacy has grown here for 8 seasons and Nocturne only one winter so far but did very well.

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All southerns will do for you is earlier bloom and more damage. And further, a bit warmer in southern NH probably has little effect on chill hours. Much of your winter is too cold for chilling. At least that’s the reasoning I’ve seen. Below freezing gives no chilling. Best chilling is 37-48F.

I hear land is cheap on Greenland. Eric the Red used to grow grain crops there around the 980’s A.D.
Be a fine investment if you have faith that northern climates are getting hot.

I’d study more history and listen to fewer stories by media outlets that have bias.

I like Sunshine Blue southern highbush blueberries. But, some years they bloom out early and the crop gets zapped here in Kentucky. The problem likely to be exacerbated in NH.

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Thank you all for your responses. Very helpful. I won’t go lower-chill. The first year I’ve experienced any blossom damage was this (admittedly very unusual) year – so no, none of my plants usually bloom too early.

Interesting about heat requirement for breaking dormancy – any resources come to mind that I could read regarding this (doesn’t have to be about blueberries, per se)? Always trying to get a better grip on what my plants are “thinking”.

I will try Legacy – I like complexity of aroma and flavor, not just pure tartness or sweetness.

(BlueBerry: no doubt that the “news” outlets are utterly hysterical and thoroughly biased. I’m seeing some real change here, though, with my own eyes. May be a momentary and cyclic blip…may not. We and all of our cherished blueberry plants will probably be dead long before that jury’s in. One way or the other, I aim to grow and eat a lot more good fruit in the meantime.)


I only know of one webpage that discusses pecan heat requirements for breaking dormancy. It is a report out of Turkey which has very low chilling hours and was having problems with relatively high chill cultivars breaking dormancy. Measurement of actual chilling hours was highly correlated with breaking dormancy after specific numbers of hours at temps above 20C. Even if chilling hour requirements were not met, enough hours at high temps eventually broke dormancy. You can see intuitively how this has to work. A tree that requires 68F to break dormancy will stay dormant at 60F and simply wait until its requirements are met. As little as 3 days of warm temps can break dormancy for some species such as peach/plum presuming cold requirements have been met.

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