There seems to be a different theory about when to divide and conquer!I think it all boils down to how bad your winters get.I think in Z-6 you can move them when ever is convenient for you. I live in Z-3 and I won't move anything until the ground thaws in the spring.In the fall the roots don't have time to get established in the new garden area,so happy gardening!

When you divide you probably will leave some soil on the roots. Then your dividing is not different than buying a potted plant on sale right now and planting it while spreading out its roots. I have done that even until the end of September and had not lost any plants over the winter in my zone 5a. The ground will not freeze until December permitting roots to grow though the leaves are zapped.
Bernd

I have divided through late September in zone 5a and never had any problem. I do always leave soil intact when dividing though.

heave is the big issue....

but it all depends how you define divide ...

it would be a fools errand to divide to single divisions .... as you would find.. in our zone.. them all out of the ground in spring.. heaved right out ...

most likely irrelevant in warmer zones ..

if you are going to cut a big clump in half... and each will weigh a few pounds ... then they arent going to heave ... ALL THE WAY out ...

if you find rocks heaved out of the soil in spring.. you know about how big they are .... so just make your clump a little heavier ... i guess that presume you have soil with rocks in it..

ken

One advantage of deviding hostas in the fall is that they are less likely to pick up HVX since they are dormant.

i am not sure that last post is correct.. as there is sap in the roots .. and if you sever them.. i dont see why you might not transfer the goo between plants ...

i am not aware of any studies in this regard ... just going on gut reaction ...

ken

Ken, check Dr. Lockhart's latest research on the AHS website. It's been mentioned several times on the forum since the convention in June when Dr. Lockhart presented his findings.

Though not specifically tested, he reported that he had a 0% transmission rate for attempts made after flowering.

According to the highlights I read of a recent address by the doctor that researched HVX, the virus was less likely to spread later in season as the plant was approaching dormancy. Also, he found that HVX wasn't spread by a contaminated knife when dividing crowns- a truly head scratching bit of info there. Seems like a lot more research needs to be done.

well i didnt go to the convention.. go figure on that ...

though your key words are: Though not specifically tested

lets put it this way .... i will let you all experiment.. and in a few years.. i will try to recall if you are having problems ...

ken

Now is a great time to divide hostas. If you are removing pie shaped wedges you will have a crescent shaped plant so divide in halves. I never have a problem with any winter heaving here in Zone 5a and I plant clumps and singles as late as the end of September. The roots have time to grow and that is what they are working on now.

Because so much is still unknown about HVX it is best to just take extra precautions regardless of who says what. Not much is very definitive on the subject yet so just get yourself into good habits now regardless of what time of the year it is. Things I used to do, I no longer do even if I end up with some ragged looking leaves and a bunch of bare half dead scapes.

I have been dividing all week. Today I dug up a big Montana Aereomarginata, split it into 4 big chunks, put them in pots, for dividing into multiple smaller pieces next fall, to sell in a garage sale the following spring (2012).That is if I don't give them all away to friends, first. Hostas I divided into single eye divisions in early July have roots showing out of the bottom of 1 gallon pots already. Monday I divided up several Gold standard I have around a gazebo to make a larger drift of hostas around it. They are many single eye plants. When the ground freezes I will cover them with shredded pine bark mulch for the winter to avoid heaving. One reason I like drifts of the same hosta ,other than it looks fantastic, is if one or two don't make it , it still looks great. Now is also a great time to move them around your garden. Hostas are FUN!

I divide in the spring and fall. In the fall, I try to leave as much soil on as possible and I replant an inch or two deeper or I mulch. I will divide until about four weeks before a hard frost. That means that I have maybe one month left.

I've never had fungal or HVX problems.

Hi there-
I find this time of year- warm-ish days and cool evenings to be the BEST time to divide my hosta.
I tend to do many of all sizes in preparation for a spring sale. I like this time of year to do this as I can see where the hosta are at this time of year instead of searching wet soil and leaves for tiny eyes, and the next seasons plants look great! My spring and summer divided plants too, seem to show signs of disfigurement until they have a winter to "compose" themselves.
When I am able to- on medium to small clumps, I do tend to remove the dirt to preserve as much root as possible. I will lift the clump- separate and actually place back in the hole at the same depth I lifted them from and mark well. Cover with soil and water. Next early spring- I can usually lift with my fingers and pot up individual plants while still very tight eyes.
I will try to do this with the HUGE clumps as well- although I will lift them and let them dry out a few days before dividing. Don't gasp- Remember the "Driveway Rule" of hosta care. The roots will shrink a bit making it so much easier to separate the large clump into smaller sections WITH great intact roots. Just be sure to water well a couple of times on warmer days before winter freeze.
I have well draining sandy soil which may make all the difference in allowing me to do this to my hosta late in the season for Z4- and not show winter rot- heaving or any setback to the plants.
When I have planted Hosta eyes below the surface of the ground- Or have heavily mulched I usually for get to lift again or remove the excess mulch which result in "lost" hosta that reappear as one eyes next year or two. I dug one up this year that had been "lost " for 2 years. Black Hills planted as a nice one eye got burried alive as it seems. It set up a stolen to the surface which grew roots and eyes. So this plant had 2 sets of roots- one clump much lower in the ground with roots and stolen- and one nearer the surface which grew leaves and roots.
Many bulbs will do this- but they will actually "pull" themselves up when planted too deeply. But who knew hosta would try that trick!
Lucky for us these plants really want to make more of themselves!

The fall it is then. Next i have to decide where i need more before I dare give any away!

Have you considered dividing them in the spring before they've leafed out?

They won't be so crescent shaped if you divide them when they're just pips sticking up out of the ground. The leaves will unfurl in a more mounded pattern.