I tried this groundcover for the first time last year. The only place it survived is in a protected area of my yard that was covered with snow for the bulk of the winter season - it actually flourished there.

In other unprotected areas of my yard, mazus does not appear to have survived, completely dead, brown, deteriorated and gone.

Many nursery tags say zone 5, but should more accurately read zone 5 WITH winter protection (mulch, sprigs, etc.) - which is consistent with what I've come across on the web.

For this reason, I would probably not recommend this plant for zone 5 unless you are diligent about winter protection.