hickory trees

hi peeps
im from Australia northern tablelands NSW big winter frosts warm summers -18 to 35*c
most of the species here are suited to warmer climates
which varietys can cope with cold the best?

The USDA plant website says the Shellbark Hickory (Carya laciniosa) is hardy down to -22C, and the Shagbark Hickory (Carya ovata) to -44C. These are generally regarded as the best nut producing Hickory trees. (Assuming that's what you want them for).

St. Lawrence's Tree Nursery has some very good cold hardy hickories although I don't know how you'd get them shipped to Australia but its worth to check it out.

-18 degrees C equals just a bit below zero F, which means USDA zone 7. Which means you can grow any hickory you want, pecans would be my personal choice but I like pignut and shagbark. I also think I have hybrids of the two growing in the woods but no seeds. Again, pecans would be my choice, and IMHO seedling trees are better; candy companies over refuse to buy named variety pecans, instead preferring seedlings, the oil content and taste is stronger so less has to be used in the candy.

I second the Shell bark (Carya laciniosa) and Shag bark (Carya Ovata) for cold hardy eating nuts. I have encountered both in Central Minnesota pretty far into the Zone 4. Pig nut Hickories (Carya Glabra) are a tasty, with a smaller nut, tree I have seen do very well in Zone 6. Black Walnut (Juglans Nigra) and Butternut Walnut (Juglans Cinerea) are both tasty cold hardy nut trees in my experience too. Butternut gets a blight that might not be an issue outside of the US.

great stuff
all i need now is a mule to get them here??