One of the major concerns when planting a tree is its winter hardiness. This aspect was largely forgotten for the first 10 years of the new millennium when winter was but a slightly colder period than the autumn, but now after 2 of the hardest winters in memory it has risen back to the top of the agenda. Of course it is not just the temperatures which can affect the survival of trees in the winter. It is well known that water logging will contribute to winter kill and also a warm winter followed by a very cold spring can damage new growth which buds prematurely. Many of the plants which died in the very cold December 2010 were almost certainly damaged because they still had soft growth from a mild November, and others were weakened by the winter of 2009/10 and a second severe winter in a row was just to much for them. So how about Cercis? The National Collection is composed of the canadensis ,canadensis var. texensis and chinensis cultivars. All of these plants are suitable for growing in the UK in even the every coldest winter.The canadensis even survive -25C every winter in the N.E. USA and Canada. The texensis is a little less hardy , but still will have no issues in the UK and while the chinensis is potentially more susceptible, in practice it is almost unknown for these plants to die of the cold in Europe and ours planted in the collection suffered no deaths even with -16C last winter.
It is possible with Cercis that in very cold winters any late summer growth will die back, but once the trees are established this is less likely to occur.I believe this is why some report the Forest Pansy not to be hardy in Scotland. With the short growing season the new wood never becomes mature enough to counter the cold and so every year the die back occurs and eventually the plant dies, however grown in a warm sheltered sunny location even here it can be ok.
In conclusion–Cercis winter hardiness–not a problem.
“So good every garden should have one”