The best time is spring while still dormant. However, if it is fairly large and well established you could cut the entire plant off at about 6-8" above the ground, dig it with as large an earthball as possible and get it into its new home immediately, watering it in well. It may not have a very showy bloom next year, but will probably live and re-establish. Spireas are pretty tough plants.

Since the topic came up........:-) Weather in the PNW is definitely an acquired taste - you either love it or you don't. I personally think the weather here is pretty much ideal - one can garden virtually year round, it is seldom too cold (although it can get cold, it's never bone chilling like many parts of the Midwest), it's never too hot, we don't have high humidity and associated problems, we get snow but not excessive amounts. And our zone 8 climate welcomes and encourages one of the widest possible ranges of plant choices - not much doesn't grow here and grow well. The drawbacks are that winters (read rainy season) are long and uniformly gray - SAD can be an issue for many. But rainfall in general is light - average annual rainfall in most areas is well below many other parts of the country. We just get a little bit over a very extended period of time :-) But when the sun does shine - and it does more than one expects - this area is spectacular. Much of it has to do with just its natural scenic beauty, but a good day in the PNW is unsurpassed by anywhere else I have ever visited and I've been everywhere in the US except for the deep South. Summers may be short but fall - indian summer - tends to be long and wonderfully pleasant. I consider September into early November to be some of the best months of the year.

Hi brightmoregirl,you should have no problem moving your clems.The only bummer is that it will set you back a year on the flowering.I would do just as mamoo said be sure to get as much of the rootball as you can and have the new hole all ready to go.Clematis are tough plants when they get past the first couple years so they should be fine.I removed some Huldines when I worked at chalk hill and the rootballs were so big I had to use a small backhoe to dig them up after I dug them up I let them sit there outside thier holes roots showing and no water.A few stayed like that for a couple weeks before I chopped the roots off and potted them up in 5 gal pots.All did fine and were sold as nice plants.

Meant to answer your personal email question but you do not have an email contact through GW!! You might want to change that if you do attempt email contacts :-) Previous answers are good - any time the tree is dormant and the ground workable (not frozen or overly saturated) is a fine time to move/transplant. In my area (actually same as the two above), JM's do not emerge from dormancy until well into March. I'd say you have several months still to accomplish your move :-))