Butterfly Bush in Shade?

I've just purchased my first butterfly bush and where we put it only gets 5-6 hours of sun in late afternoon. This one is 'Pink Delight' and I'm also considering getting 'Nanho Purple' to put beside it.

Is it going to be ok in this area or do I need to move it to full sun? (I'd like to leave it if possible).

Will Nanho Purple be ok in my zone? It says hardy to zone 5b, so that concerns me.

Thanks for your help :)

Buddleja does best in full sun. A little shade is not usually a problem, but I think you are pushing your luck with just 5-6 hours of sun.

When it is in the shade, is it bright shade, like under an open, airy tree with filtered light? Or is it dense shade, like from a building or denser tree?

Certain nanhoensis varieties are rated for zone 5. I think the cold tolerance in the winter is the deciding factor. Not every part of a zone is the same. There is a range of conditions that are found in each zone.
This difference might be this:
Even if your property is right in the middle of the map, solidly in a zone, there can be cold spots or milder spots within that zone. The north side of your house is highly likely at the colder end of the zone 5 specs, and a warm south or south-west wall might be a little milder than typical zone 5 winters.
Perhaps there is a cold wind channeled by some hills, or the other houses.
Your house might be near the bottom of a hill. (cold air tends to settle at the bottom of hills, and in creek sides)
Conversely, it would be warmer than average on the protected side of a hill. Not at the top- exposed to the chilling/drying wind. Not at the bottom where the cold air drains to.

The only way to know these places for sure is to live on the property for a few years, and see what happens when you try to grow marginal plants. If you have a lot of luck with plants that are not listed for zone 5, then you might think your property has a sort of 'banana belt', a warmer pocket than is normal. If you consistently lose plants that should work in your area, then you might suspect that your zone 5 might be at the colder end of the spectrum.

When you purchase the plant, get it in the ground promptly, and use the right fertilizer and watering to get its roots established quickly. Do not look for leaves or flowers. Yes, top growth is important, but cold hardiness will come in big measure from a well established root system.
Protect the plant its first and probably second winter.
Watch the weather reports, and if a sudden cold snap is expected, protect it.
The same cold, after several weeks of gradual cooling might be fine. But a sudden chilling might kill the plant.

In the coldest winters where Buddleja survives it will go completely dormant, and lose its top growth, perhaps all the way to the ground. Certainly to small nubs of branches. Recovery in the spring comes from the root system. These plants are treated more like a perennial than a shrub.

Thank you so much for all the info! The Pink Delight is in a dense shade, so we'll look at moving it to another location that's full sun.

We won't be buying the Nanho as we definitely have a wind tunnel in our back yard :) As soon as I read your description of wind being channeled by other houses, I felt like you were looking at our house! Our yard slopes down to what I refer to as our ditch and so do the surrounding houses - the backyard faces the west, so obviously the north winds get wicked back there!

Here's a pic looking down to the 'ditch' after a good rain - the city has an easement that says we can't plant anything in the ditch because of the drainage. I keep threatening to put in pussy willows LOL.

Again, thanks for your help.

Are you allowed to decorate the ditch with some nice boulders? Outside the main water flow, perhaps?

No, nothing can be put in - but I'm badgering hubby that I want a small bridge so I can get across to my shrubs without having to jump the water :) We'll see how long it takes him to cave in LOL