Hopefully you'll find someone who has actually tested it but seeing as it was developed in Tennessee, I'd say it's doubtful that any additional hardiness is anything more than accidental.

Its parents are "Ruby Falls" & "The Rising Sun" if that helps you any.

Black Pearl Redbud patent

Interesting.. why do they sell these things up here? I saw it at a nursery (Bradford Galleries - you may have heard of it), which is north of Hiway 88!

How's the Heart of Gold for hardiness? My straight species redbud is doing well.. I can swear it doubled in size this year and that's conservative..

I'd like to plant another redbud but with a different leaf colour just to add some variety...

When the standard Cercis canadensis was first offered regularly for sale in Ontario (~20-25 years ago), the seed source must have been southern because I still see those trees regularly dieback (sometimes to nearly the ground) in Kingston. More recently (last 15 years), the growers are providing much hardier standard Redbuds to nurseries and those newer trees are completely hardy. Sourcing Redbud seeds from northern sources is even better as seen with the success of trees at Ottawa's Dominion Arboretum.

As for the named varieties, there is always a demand for novel traits so they continue to be offered even if they don't pass muster with hardiness.

Enough Americans in northern states have the same issue so you should be able to glean Redbud variety comparative hardiness from this & other garden forums/blogs and make an educated guess what will work in Ontario. From personal experience (& supported online), Lavender Twist is also quite hardy with no dieback in Kingston. You could use that as a base when you're reading those posts on relative Redbud hardiness. Look up patent information as well...if the parents are known to be hardy varieties, their progeny are probably as well.

It doesn't have any of the unique foliage/structural characteristics as some of the other popular redbud cultivars, but 'Northern Herald'/'Pink Trim' is a good bet if winter hardiness is your main concern. It was developed at North Dakota State U. and has reported flower bud hardiness down to zone 3b.

From the link posted above:

• Garden performance: Plants of the new Cercis have been observed to have good garden performance and to tolerate wind, rain and temperatures ranging from about −23.3° C. to about 37.7° C. and to be suitable for USDA Hardiness Zones 5 to 8.

Well we got down to -25 at least twice last winter.. maybe even colder.. and my straight species cercis made it our fine after its 2nd winter...I had to think about it because in my first post I may had said it was the first winter.. there was some minor dieback but it wasn't established.. just a couple of twigs... what didn't happen was that it didn't bloom this year because of a brutally cold spring we had in this region. It snowed as late as May 9 - yes, it's canada but that is late for us given that we are in the South and have the same climate as Michigan, Western NY etc..

I might just plant another straight cercis next year...

I just purchased one. Houston summers can be relentless. This one is around 5' tall and I placed in a big pot doing this to move around to confirm a great location for it before I put in ground. This is done to make sure the location is best for the tree and not the other way around. It's a beautiful tree, just needs some TLC.