Adding more soil and mulch is a good thing..I wonder if the freeze and thaw from winter could cause such a thing..of course being a Southerner..I've never experience it but have read of such ocurrences up North..Jeanne

Ditto to what Jeanne said. Freeze heaving is common up north but not something us southerners know any thing about. I would be tempted to mound soil up around it at least or if it truly is mostly above ground, dig it up and replant it now.

I am in zone 5 & never had a clematis heave the way you say. Could it be that last summer/fall was so dry that it came toward the top of the soil in search of water? That is the only guess I have. I would lift it now & plant it deeper by 5". It should take off for you. Some of the top roots might be damaged but the others should be ok. Waiting until fall would not be good unless you put it in a pot for this summer & then wait to plant in fall.

It just totally blows my mind that it heaved out of the ground. It's been there for years and I have a soaker hose on that row of clematis. I can see the crown and about 4" of root. The heck of it is it's already started up the trellis. I'm afraid I'll break off the crown if I mess with it now.I really don't think it went into the winter dry, but I guess anything can happen anymore. I've had iris and daylilies heave before, but never this.

I've seen frost heave, but usually it's just frozen water sticking up out of the ground (very disturbing looking). I suppose if the water were under the plant and the soil was loose, it could heave the plant out.

I'd just mound mulch/soil over it to protect and cover the roots adequately and leave it for now. Later, in early fall as it nears dormancy, you could attempt to rebury it properly.

Like some of the others, frost heaving is not a situation I have firsthand experience with and I'd have a hard time imagining how it could lift an entire plant with a root system like a clematis out of the ground. Perennials I can understand as they have relatively shallow root systems. Does this happen with shrubs?

I think what normally causes frost heave is that things are planted too late and don't get sufficient roots down before winter sets in. What I don't understand about this is that it had been in the ground several years. I've never had a shrub do this but can't say it might not happen. If I get an iris or daylily planted late I sometimes lay a brick over it until spring.