This is a great time to divide and transplant.

even the highly experienced.. have doubts ... crippling anxiety ... do it all the time myself ...

you know the answer.. just do it.. thru about early oct ... the only issue i see.. is if they are too small.. and might winter heave .. dont know if thats an issue i your area ... if small.. sooner the better ... more time to settle in ...

the alternative.. is if you think it might dry rot.. if left in the bad place.. if so.. move now ...

6 of this.. half dozen of the other.. but i suspect ... that odds of failure are high.. either way ... so you may as well give it your best shot and go for it ... whats the alternative.. you do nothing.. they die.. then you blame yourself for not acting??? .. its the ultimate catch 22 ...

when you get to this point.. dig them up.. throw them on the driveway for a week.. show them who is boss.. then replant ... live or die.. but at least i did something ... and if you are that much of a weakling.. i dont need you anymore ...

ken

Ken I just wait for your left handed compliments! Actually I just talk about these crippling decisions

i usually don't act on them

and what you describe usually happens: the plants in question stay the same, grow, or die.

i think that covers all the options.

I mentioned recently that p.Golden Arrow is struggling in dry part shade in a very dry summer.

I hear you Marie. I kept my GA going through this dry summer with regular watering and now that it is the cooler wetter fall they are doing their thing.

I consider it a great Fall perennial. Here is one of them just today:

Looks good. I transplanted the two that survived to more sun and better soil. I just have to remember to water them.

When I am uncertain about the best times to divide and transplant, I have a rule of thumb: everything which flowers before the summer solstice (campanulas, dianthus etc.) can be divided in autumn. Those which flower later in the year (asters, rudbeckias) are always left until spring. It is a timing issue which has, so far, not let me down. Persicarias would count as the latter group so I would be waiting till around April.

I am now afraid to say that Ken-type advice comes with a warning...the man is a lawyer - forked tongues run in the profession...you are, at least, not being charged an hourly rate - although I now understand his blase attitude towards the survival of (costly) plants. (smirks).

I like the idea of dividing later flowerers in the spring (as per Campanula), but I have two big problems here. We have a late spring, with March spent trying to help the birds and other wild life, April dedicated to spring bulbs and May to most of the spring perennials. The ground is also wet (we earnestly hope) with melt water from the snow. The second half of June tends to be a slow time for the variety of spring perennial flowerers.

The first thing is that it's not great to trample wet spring beds and potentially damage spring bulbs and May perennials. By mid June you can't even see much of the soil surface.

The second is that although I tend to be obsessive about perennial cultivar identification (have maps, etc.), I still can't often tell, in spring, which many of the summer and fall cultivars are which. Too much Phlox 'Peppermint Twist'; I don 't want to divide/sometimes even eliminate the P. 'Twister' instead.

Re Ken and survivalism, I'm a bit of a natural selectionist myself, at least with respect to the garden. If a plant can't be bothered to live (OK, that is a bit of an oversimplification), who am I to protest? That just makes way for new opportunities. I've said it before, gardening is as much about destroying as creating. It's only when our perennials can afford Ken's legal services that I'll get worried.