Chill hours I thought were anything under 10 degrees (Celsius, of course), but I gather officially it's probably closer to 7 or 8 degrees. Sub-zero isn't necessary, in any case.

You're right that they've doubtless been selecting for quite a while at their site - and will therefore have varieties that are happy with chill hours for the region.

Though I'm surprised they get as cold as -3 given how far north, and how close to the coast (20km) they are.

Lismore - to their west, away from the coast - has an elevation of only ~10 metres. The township they're closer looks to be Wollongbar, and that's showing as ~160 metres elevation. I believe the soil around there is superb (volcanic, not depleted like 'average Australian farming land') which is probably a bigger factor.

I'm south of them by 4 degrees, same elevation, and have Much Optimism for my half dozen new blueberry plans ... once I get them out of pots. Shame that these Eurekas plants don't seem to be for sale.

EDIT: meant to add - some varieties that are popular here in AU - Sharpe Blue, Biloxi - have low chill hour requirements, around 300-400 say, BUT really don't like frosts, so it's quite the juggle.

The Northern Rivers area (where Lismore is) has a lot of gullys and valleys, whereas the towns there tend to occupy flatter areas. Winter in the gullys gets bloody cold. The official temperature in Lismore is measured at the Post Office. I grew up in the Northern Rivers, and saw frost most years in the gullys and on the slopes of our farm. We were closer to the coast than Lismore, so they'd get more frosts than we did.

> Still seems like they've made some progress on reducing frost requirements.

Most likely, it's just that the common assumption is that all of Australia is hot and miserable, whereas not all of it is. They're not actually in Lismore, they're near it.

My blueberries fruited without needing frost (we get none where I am in South East Queensland); it's definitely been bred out of them as a requirement I think?