It depends on your soil, etc. There was a thread about this subject about a year ago (?) and different people had had different results. If they are happy, the common ditch daylily can quickly take over a large area and become a real nuisance.

If they are happy ANY day lilly can take over, if you let it. In fact, most perrenials can if happy enough.

That's one of the reasons you dig and divide them every so often. It keeps them in check, promotes more blooms and gives you plenty to plant elsewhere or share. (All perrenials, not just day lillies.)

I definitely don't agree that most daylilies can "quickly take over a large area and become a real nuisance". But, to set the record straight, the common ditch daylily can be orders of magnitude worse than most other daylilies.

I suppose "quickly" is a relative term as is "nuisance". All day lillies spread, right? I could be misinformed on that one, but if they are happy they will spread. Maybe the more refined cultivars grow slower or are so finicky that they choke themselves out quicker, but they all spread.

I tend to garden in the long term and count on things spreading and needing dividing periodically. It's a war of attrition. *grin*

So would you move them or just divide them? About how often do they need dividing?

Clumps of 2' or more in diameter should probably be divided and thinned out. I would think that if they are in a bed where Hostas are doing well that it is mostly shade. Most Daylilies on the other hand bloom best in full sun so if it is a shade bed then the Daylilies ought to be moved anyway.

Joe is correct in that terms such as "invasive", "quickly" and "nuisance" are all relative. Anything that moves in a bed where you don't want it or begins to spread thicker than you wish are a quickly, invasive nuisance. :-) Brandon is right in that "ditch lilies" are much more apt to spread quicker than other Daylilies. Post a pic or email me a pic and we'll be able to give you better info.