Circling back to Annemarie's original tip, let's take Moby's hardy hib as an example.
If you went to Home Depot or WalMart and bought this plant, the label would maybe say "Full Sun" and Zone 4 - 9, no matter where you are. Most places in the northern 2/3 of the US and southern Canada you'd be fine following that info. But the further north you were, the more sunny a location you'd have to find. I think the labels would be more useful if they said "All Day Sun" for more northern states and Canada. Again, I'm saying you just can't define the term "Full Sun" as 6 hours. It depends where you are.
But they do grow and are sold in the rest of the US as well, and (although I wouldn't) if I did get one, I'd plant it in partial shade on the north side of my house so that it would get only morning sun in summer, and be fully shaded in winter to try to give it more of the dormant period it needs.
Anyway, growers that sell online tend to give more, and better information. eg. I shop White Flower Farm sometimes for gift plants for my daughter's garden in Salt Lake City. Their perennial plant descriptions give a range such as "Hardiness Zones 5 - 8 S / 5 - 9 W " the S meaning South, the W meaning West. Thus they aren't recommending that particular plant for Zone 9 in the South but it is ok for Zone 9 in the West because they are very different. They also say "Full sun to Part Shade" for most of their perennials and shrubs with a wider zone designation. So they're giving it a range, and the gardener must make a judgement call depending upon where they live, as to how much sun to give that plant.
Even places in the same latitude - same day lengths - have varying sun intensity because of altitude. eg. Salt Lake City (4500ft) and Denver (6000ft.) have more intense sun than New York City so the same tomato might ripen with only 4 hours of "Full Sun" in SLC and it might take 7 hours in NYC. Air quality plays a part, as well.
Just sayin' !! Don't generalize, and don't believe what the labels say anyway. Make a judgement based on your own climate in your garden.
Here's an 'Easy Does It' rose, very happy with only morning sun here.
