Did they bloom already? If so, I would do it now and get them in the ground to give them a chance to get well established before winter freeze sets in. Night temps are cooling off where I am (50s-60s), so the beginning of good plantin' time is upon us...

If they haven't bloomed yet, I would wait - enjoy the blooms! You can divide and plant after blooming. :0)

They are just starting to create buds. Definitely want to enjoy the blooms!lol!

I had bad luck my first year with them...probably my fault. More clay like soil and planted them in late September. Never came back.

I planted them again spring 2010 but sold the house...curious if they came back. I'll have to do a drive by!

Since they're potted I would plant them but I wouldn't divide them until Spring. I find Mums apparently take a long time to recover from transplanting or dividing in the fall and aren't apparently working on their roots. In Spring you can do anything to them. Mine always come back except the ones I transplanted around the yard in the fall. I have some starts in containers this year that I want to see if they are going to overwinter in them without protection.
Cher

mums in production for sale vary widely as to long term viability ...

for a while.. i collected a bunch.. i would say about half of known mums are z5 winter tolerant ...

but that does not say that a producer uses such for sale in your area ... the ones that produce best in a greenhouse to look stunning at sale time.. this time of year ... are NOT necessarily going to live over the winter ...

so its a roll of the dice.. unless you order from a seller ...

i would not do it now... enjoy the bloom ... do it in early spring.. if there is anything left ...

all that said.. one of the easiest plants to root in a glass of water .... cut a few 6 inch pieces.. cut off the flowers.. and as soon as you see root nubs.. sink into peat based potting media .... and tent them ... this was exactly how my seller, way back when.. sold them ... they are out of biz now..

ken

Thanks everyone. I ended up just planting them to get em in the ground and hope they establish somewhat over the next 75 days or so.

Ken,

The same rules apply to planting these Mammoth mums in spring and well drain soil but they are zone 4 hardy. Introduced in MN. Its quite annoying because no one sells zone 4 or 5 hardy mums (there are quite a few) around here...at least they are hard to find. I have Sheffield as well which might be zone 4 as well.

well if you leave out pertinent facts.. then you get shotgun answers.. lol ... you would save me a lot of typing if you did give all the facts up front .. lol ... i hope you have one cutting in a glass of water in the house.. just to prove me wrong ... its got time to root and be stuck in the ground by mid sept ...

and.. as with conifers.. mail order will get you what you want ...

i am still trying to recall that name of that mum seller.. they offer ... back in the mid 90'2 ... like 500 varieties.. FOR TWO BUCKS EACH ... they were just single stemmed rootings as i said.. but at two bucks.. i think i bought about 25 varieties.. it only took a few years.. to be down to 10 or so.. truly z5 hardy plants.. but it was neat .. because they were much different than the usual bigboxstore offerings...

it was a short family name .. lee's???? ... .. whatever.. odds of someone popping in and reminding me are low ...

ken

Damn, I thought I picked up two Red Daisy Mums and one was Coral Daisy...little tag was at the bottom of the pot!

Well if they make it through I'll have 4 Reds and 4 Corals.

I actually really like mums and late blooming plants for that matter. In spring your so happy to see green that everythign goes by in a blur. By late August you're so used to green and so many plants have tuckered out.