Transplanting a mature hollyhock is iffy, at best, at any time of the year. You're likely to kill it simply because it has a taproot that doesn't like being disturbed. If you've got seedlings with a good root system that are 5-6" tall, those can be relocated fairly easily. However, I'm sure there's a poster out there who moves mature HHs with great success. I'd also let the parent plant bloom out and save the seeds.

"Donn can get away with transplanting in the fall.." I'm getting spoiled. I also moved from Ohio, the NE snow belt, but I moved from 5 to 7, and the luxury is dramatic. That said, I did quite a bit of fall planting and transplanting in NE Ohio. First frosts don't stop cool season perennials from growing, especially their roots. Even in zone 5, it takes a good bit of sustained, well below freezing weather to freeze the soil below the surface. A rule of thumb I use for fall planting is to avoid disturbing roots. If I can install a potted plant without having to tease, cut back or otherwise disturb the roots, I'll do it. If the plant is pretty root bound, I leave it in the pot, and bury the pot. Sometimes, the roots will grow out of the drainage holes and into the surrounding soil, but when I pull them in early spring, they are usually getting a haircut anyway, and a little root pruning just stimulates new root growth.

yes you must ... nothing is going to grow up thru 12 inches of soil ... first.. if you want 12 inches.. think about adding 15.. so that when it settles ...you actually have 12 .. much more important.. at the lower end.. if you want 6.. and put 6.. you might end up with 3 ... next .... take out the plants on one side ... improve that area .. jam the plants back in ASAP ... close together ... simply to HOLD THEM OVER... remove other half to the new area.. still jammin ... lol ... do second half ... then anytime next summer.. start moving them around ... with this method ... you can make it a 2 weekend project.. it just gives you alternatives to killing yourself on a none day project ... ... presuming this isnt checkbook gardening ... and you will have a 10 man crew out there ... the VERY MOST IMPORTANT VARIABLE... will be tracking down.. and securing GOOD SOIL ... this is not simply going to be calling the closest place.. and ordering up a truck full ... you want to find a good peat based soil ... with some amount of sand for drainage.. perhaps a new post.. if you wish to discuss soil science ... so pay up front for good stuff.. and you will be rewarded ... now ... the real question.. is 12 inches enough ... for high compact clay ... if you are hoping to garden COMPLETELY on top of the clay ... you might want to consider 18 to 24 inches ... i do NOT know ... but the one thing i do know.. DO IT RIGHT THE FIRST TIME... there have been too many garden projects in my life.. that i finally won.. THE THIRD TIME I REDID IT.. lol good luck ... ken ...

It could be done but you do increase the risk of loss because of the nature of a decidiuous plant is to store energy in the root system as it goes toward dormancy. You may be better off to wait for early spring. In S.A. think late Feb- first half of March. That way the smaller rootball will have more energy stored and it will begin growing in late March or April depending on how warm it gets how soon. Hope this makes sense and is of some help. If not repost on Tx forum as I monitor that more than this one because it is more active. I like this forum mind you but it is not as active as I wish it was as I love all forms of hibiscus and love to learn and share with others on this topic. Good Luck and as always... Happy Growing David