Cercis canadensis, redbud's hardiness

In all the catalog where I have seen it listed, the redbud is claimed to be hardy to zone 4. I live in zone 5a and I have not seen any planted nearby. Yet, when we travel 200 miles south, closer to NYC, they are everywhere, they are often planted in the rest areas there and they look so lovely in the Spring. I would love to plant one but I am afraid it is not as hardy as supposed, does anyone that live in zone 4 and 5a have any experience with these?

I have seen them in 4b and 5a. They will last most 4b winter's, but I think their bad number is -20 - 25 which will show up every 5-10 years. So it's risky to invest much in them.

Perfectly hardy here in Z5a, (now changed to Z6 with the new map), but we have had -22 with no damage to the Cercis Canadensis. I have about 20 of them. Some of the cultivars are not as hardy. Funny the first one I got was from Michigan Bulb, probably 20 years ago, it was about 4 inches tall, and it is now a huge tree. We have significant snow cover, which I suspect you do also, that helps many plants survive, but never any tip dieback, or bud damage. It is a fantastic tree.

Living and flowering well here in the Champlain Valley of Vermont.

Thank you guys for your input, I live about 60 miles south of Montreal, not far from lake Champlain, we cannot count on always have a good snow cover here but it can thrive in the Champlain Valley so I think I will take my chances and get one, they are so beautiful in the Spring.

Everything I've seen says that their hardiness depends a lot on the seed source. (If the source is from a colder area, the progeny that aren't cold hardy don't make it, so eventually the gene pool produces hardier plants.) With that in mind, I got mine from a nursery that carries plants from Bailey Nursery in MN. They have a seed strain that came from MI or WI and is supposedly hardier than the run-of-the-mill redbud. I've only had mine two growing seasons, so it's on its third NH winter (the first was in the nursery.) So far it's doing quite well, but winters have been a bit milder recently, so I'm not sure it's a good test. I've seen ones several years old in Plymouth, NH which is solid zone 4, but I don't know their source.

Has any one seen the Weeping Redbud LAVENDER TWIST at a local nursery in New York metro area?

I found quite a few nurseries that carry Baily's plants around Burlington, VT. It would be a nice ride to take this Spring. Another way, I could order from Nature Hills, Nebraska. Howerver, it is always nice to buy directly from a nursery, although more expensive, the plants are generally quite a bit larger. I prefer quick results when it comes to trees.