Basically, if you're dividing plants in fall you want to balance 1) giving them as much time as possible to make food during the summer of heat and sun and 2) gving them as much time as possible to grow new roots in the new location, before the ground freezes. I've planted stuff as late as November, but wouldn't recommend it, even for bulbs, if I had a choice (tho' I'm almost a zone 6 here at my home). Best time would be late September, I think. You can cut back your grass either fall or spring - many people wait until spring just because the winter grass silhouette is prety. The only reason to wait on the cut-back (and the division) would be if the grass is only marginally hardy. In that case, leaving the stalks on until spring would offer some measure of protection for the growing points. FWIW, hostas survive just fine when divided in the spring. Just do it before the leaves unfurl, or you'll go nuts. I've even divided medium-sized varieties when they were in leaf, because I didn't get to them earlier. If you really want a challenge (not that I'd recommend this activity) try moving a relatively mature specimen of one of the big blue hostas IN FULL LEAF! I did it once because I was offered a free specimen of Frances Williams, and the person was moving in the middle of summer. That plant is still the centerpiece of the bed in front of my house.

and I'm itching to move them now, but planting is not the same as transplanting. ===>>> yes it is ... its all about root disturbance.. interfereing with water movement in the plant ... and dealing with all the attendant variables ... this answer you wish is highly zone and location specific ... and you should rely on those near you or with such experience .. like sara and embo ... and gal ... the other answers.. are correct for their locations ... and that sums up.. if you searched the web.. perhaps without knowing some experts location/zone.. you got all confused ... they arent wrong.. they just arent right.. for you ... my MI is so not your CA ... that i am not even going to hazard a guess for you .. ken ps: i think you meant that digging and cutting off roots.. is not like planting a potted plant .. but even that.. done right.. usually involves severe root pruning due to circling roots.. so after all is said and done.. they are about the same.. not different ...

Geez. I'm saying that in the PNW and Central Texas, both 8b, the FIRST FROST dates are within a couple of weeks of each other, and the LAST FROST dates are within a couple of weeks of each other. No one ever said that first and last frost dates were related. You didn't answer my question. But you're right. USDA zone IS representative of the coldest winter temp. I'm amused when people start blathering about USDA zones as deterministic for summer gardening. Summer gardening in the PNW is nothing like summer gardening in Central Texas. Been there, done that.

In your zone, I wouldn't hesitate about planting now. However the tiny clematis starts I purchased early this year and potted up are not yet ready or fully enough developed for me to plant out yet so will wait until spring for those. It will probably take me until spring to figure out where they are going anyway :-) I have no idea where there is room enough for them all and I probably should not have purchased them.......but they were just too cute and too cheap and I couldn't resist!