I have been thinking of doing the same thing. Usually I divide in Spring. But it depends on the type of plant. Also will need to be watered in really well until the rains pick up again. What plants are you thinking about dividing?

Good question romanticdreamer. I have a few perennials that are way too big and should be divided. When is the optimum time to do this?

I bit the bullet a few weeks ago and have been dividing and shifting a few things.

My astilbes looked terrible .... should have been divided this spring so I figured they couldn't look any worse than they already did and just dived in. I also moved/divided some irises. Everything looks fine, considering and I'm very diligent about watering.

I also made a new flower bed and dug up and moved an azalea and shifted two hydrangeas that weren't blooming. Haven't lost anything yet, knock on wood. ;)

Thanks for your input....I went ahead and did like Dawn did, shifting plants mostly. Some I know won't look like anything until next year, but I don't think I killed anything. I took some Miscanthus out of large pots and planted them in the ground...dug up Calla Lily and put them in pots....dug up Gladiolas where Cedar tree roots were choking them and moved Sedums from another spot and put there, thinking they might contend with those roots....I dug as deeply as I could and cleared out the Cedar roots, so they should be OK for awhile, anyway.

Ideally, spring blooming perennials should be divided in fall, later season blooming perennials are divided in spring. But......in our climate that can often be fudged to some degree :-) Really tough plants like daylilies, hostas, hardy geraniums and most non-woody groundcovers can be divided just about any time you are in the mood.

Some perennials are pretty fussy about the specific time you divide. Most types of iris go dormant after bloom and that's not an ideal time for division.....they just kinda sit there doing nothing and in hot, dry summer weather (not that we necessarily have had much), that can be unnecessarily stressful. Ideally, these respond best to early fall division or transplanting as they emerge out of dormancy and their roots become active. Almost the opposite with warm season ornamental grasses -- as the season cools down in fall, they begin to enter dormancy and they generally do not respond well to a late season division, as their roots become more or less inactive. Also not a great idea to plant them or transplant them at that time of year, especially if we have another excessively wet winter. If the roots are not active and don't have sufficient time to establish before cold, wet weather sets in, they simply just rot out over winter. So watch out for those 'great deal' fall sales on certain OG's......they may not be all that great if the plant doesn't survive our winter. Cool season OG's no problem :-)

Not all types of perennials need or respond well to dividing. Generally those with more or less permanent woody frameworks - lavender, helianthemums, lavatera, erysimums, etc. - don't require or respond well to division. You can usually tell if a perennial requires dividing if it starts to die out in the center with all the active new growth forming a donut around the periphery or flowering falls off dramatically.