I planted some perennials last spring that became remarkably huge this year. They look very overcrowded, but I didn't divide them in early spring because I didn't expect them to be so big! The plants include black-eyed susans and a hosta. There is also a white flowering plant and a yellow flowering plant I can't identify. They are in the first photo, from last summer. I am in Toronto (mid June). The plants are quite advanced (the yellow flowering plant has buds) as you can see from the second photo. Is it too late to divide and spread them around now?
what zone are you in?? i'm in zone 6 and i wouldn't have a problem splitting/moving them at this point in time. usually, that is - right now we are in a 'heat wave' and it's been close to/at/over 90 farenheit for the past week and will be in the 80's for the next week. so, for me, i won't be moving or splitting what needs to be done - i'll have to wait until the weather calms down a bit or do it next year if the temps stay like this through mid-july. if you're in the same zone or lower and are having normal temps for this time of year, go right ahead and split/move what you want to. just make sure to get as much of the roots as you can (and leave the soil mixed in with them) and water frequently until they get re-established. the hosta i would wait until the blooms are done with. or maybe do that one in the fall...although i don't have any, i seem to be thinking they should only be done in cooler temps. the second pic, forefront, looks like coneflower. you can split them out...just expect them to pout, big time! they'll need frequent watering to get re-established and fiddling with them will cause the moved portion to have a bit stunted growth. best to get them done now though so they have some time to get the roots situated before winter hits. only other choice is to wait until next spring when they're just starting to emerge. the bes will also pout a bit and will need plenty of watering. can't help with the other plants for id's. generally, you should be okay with splitting/moving. it's still early enough in the season and there's plenty of time for them to get situated before the cold weather starts.
just looked at the pics again before closing them out...the other yellow one looks like some kind of chrysanthimum. i could be wrong on that as there are a few other things that look similar (and i can't recall their names at the moment!)
Looking at your photos, it seems to me the clumps are not too big but too close together, having been planted as babies. How about just leaving them for now and once they start to go dormant, move them all a little farther apart? A good excuse to enlarge the border! Then they will all look fab next year.