I would think where you live it shouldn't matter too much, but most plants of this nature seem to enjoy the winter months to establish a good root base before our hot weather sets in sometimes quite early in our area. That is unless we get another year like out last one. For me I find many do best given that early start through our winter season.

I know that it looks nice when controlled, but in z8 and warmer, it's rather invasive. Where I live, people try to kill it off.

I have english ivy on one of my trees. I'ts cold and tonight will be in hte 20's here but that ivy just keeps growing.. TRUE it is invasive but if you like it alot you just cut it and put it somewhere else. My neighbor across the street has put in on the ground of her chain-link fence and it's growing up the fence! SO beautiful! We live on 5 acre lots here so there lots of space and lots of things you can do with ivy.. It will grow accross the grass - everywhere.. just run it over with the lawn mower and it will make more. But as for WHEN to plant it? Now is good ! It Lives! Even thru our freezes.

I have lost 2 large oak trees to it. Over 50 ft tall each one.
It took about 3 years to strangle them. Best advice--Don't let it climb the tree.
princealbert