Heuchera can be divided in spring or fall, unlike some fussier perennials. I haven't tried it in early summer, and I imagine that it would not be too happy but that it would recover, given *shade* and water for a week or so. You might consider planting it "as is" and dividing it in September, unless you're planning an event where you need things to be "finished" (as if gardens are ever finished!).

My own preference is to always buy the smallest plants I can find, so I shop at nurseries where I know they'll have everything in 3 inch pots. I'll take a tray of small divisions or seedlings over a gallon pot any day - within 2 weeks the small plants will be well on their way to looking as good, and there will be a heck of a lot more of them for the same price. Some plants also get established much more quickly at smaller sizes - less problems with that mis-matched soil type barrier problem.

Divide away! Tough, tough plants. I did some large Plum Puddings last week.....it got hot the next day but they didn't lose a beat. In fact, when I was gardening in very HOT Denver for years, I'd many times buy the large pots and then divide. Reason being, the roots were much deeper than the little guys and they'd hold up to dry conditions better due to that. Use a bread knife or small saw to cut through....

I am shifting away from fall planted perennials. Last winter, I lost dozens of fall planted ones. I just don't think there's enough time for root development in our winter come early or lately climate.

Whatever I divide or plant in fall will be early, so there is a good two months of growth time.

I agree with you idabean about fall plantings. I lost some perennials this spring due to just "shoving" some stuff in the ground in Oct. (Toooo many plants!) With our whacky winter, I lost them. I'd rather divide/plant in hot conditions than plant in fall.