I think you have to select plants that are hardy to at least one or two zones colder, at least, minimum. I've grown perennials in pots for years and the major problem, mainly down here in coastal Virginia, next to the Chesapeake Bay,,, isn't the cold here really so much, but the tough summer heat, that lasts into September! It's alot of watering, but there are ways to try & shade them. I can't imagine it's too bad there on L.I.., except maybe windy? So I wouldn't suggest anything that's underpotted or too small, or might dry out too fast, or can withstand a bit of drying out, if you can't be presnt to water, and then get blown over, from being top heavy. Plastic pots are o.k. if large, jas that they don't dry as quick as clay, and these absorb water on the sides, which from wetting and evaporation can actually be used as a method to cool them down a bit, on extremely hot days. I've seen some sprayed with paint, like granite. Some pots I have, are something like hard polyurethane, but light weight too.
Well, unless you can get large sturdy glazed pots , like the imported ones from the southeast asia, they ship to here. But they retain alot of heat! Actually baked a daisy, last week...But heat loving old fashioned (antique- like ;Souvenir dela Malmaison) ) roses love it..
Otherwise, of course maybe you can store them while still planted ,in a garage, on the dry, just barely damp side, during winter?
I have to store dahlias, some winters anyhow, or they may rot if left inground. if enough snow or ice, ever actually accumulates. So I either store or eventually end up having to replace those.
I've even used big bushel baskets, that were from Blue Crabs, to successfully pot up perennial plants on a southwest wall., since the thin wood doesn't absorb & retain as much heat. But thta may be too country style, for longisland..

I left a few little hostas, day lilies and a veronica in some temporary (greenhouse) pots over the winter (sorry... I forgot about them!) and they all came back this year. The daylily and hostas didn't surprise me much but that's the only experience with that I have.
Not sure what your situation is but I knew someone who used to do only perennials in containers and, come fall, had a spot on the side of their house where they'd plant everything for over the winter.

The rule of thumb is a perennial must be hardy two zones colder than your garden in order to survive winter in a container. The delphinium, coral bells, rudbeckia, Siberian iris, agastache, spirea, columbine, hosta & balloon flower I have in pots/containers came through the past few winters, altho' they were kept up against the house foundation on the north side where they were somewhat sheltered. Going by the rule of thumb, some of them shouldn't have made it.

just about anything can be grown in a pot.. or we wouldnt have much of a nursery trade ...

the issue is more along the line of potting MEDIA ... and what you do with the pots in winter...

media is a way to predict and maintain moisture ... its simply not dirt ... and finding the right container mix... can be a lifetime quest... i am sure there are thousands of GW post about such.. and use the search engine for Al's gritty mix ... wherein the subject will be discussed ad nauseum ...

a vast majority of winter death ... is due to too much water on a DORMANT plant .. which is a function of the media... but also.. simply laying your pots on their sides... so winter rains and snow.. simply do not accumulate in your media ...

and finally ... a dormant plant.. has dormant roots ... and temperature maintains such .. so if you leave a black pot in sun.. you can warm the media ... and bring the plant OUT of dormancy ... and then it will be shocked.. when that night.. the temps fall.. and it goes back into dormancy ... so many pot peeps... insure that their pots are tipped over.. and ALWAYS in full shade ... such as stacked on the north side of a structure... NO WINTER SUN ...

up here in the great white north.. it is also imperative.. to protect your pot itself... as they can crack in the freeze thaw cycle... but since you are z7.. i dont know if that is an issue... so i wont belabor the point ....

so... to sum it up.. its not the plant.. as much as the media... the pot.. and the sun ...

good luck, and do try that search engine ..

ken

Where you are there is a fairly large selection of perennials (as well as smaller shrubs) you can grow in a pot. I think that your biggest worry will be freeze-thaw cycles damaging the pot, so choose a material for your pot that will survive that and/or provide some type of shelter or cover in the winter. I usually just bury my pots in snow to keep them frozen, but I think that you probably don't have that option. Some winter alternatives include:
Turn pot on its side to keep out winter precipitation.
Place foam on top of the container after the plants have died back for the winter, and perhaps lining the inside with foam before planting for insulation.
Move under the eaves in a shady spot for the winter to keep away precipitation and sun.

Be sure to use an appropriate soil mix for long term growth, and be vigilant about watering and fertilizing per the plants' requirements since the plants can't send roots out further than the pot to look for what they need. Every year or two you will need to remove some of the old potting mixture and add some fresh.

I really appreciate everyone's response and suggestions. I have about a dozen concrete planters that are about 12" high and about 12" wide. If I'm able to keep Iris or Hosta in them throughout the year, that would be fantastic. Since we're already into July, would you suggest waiting until spring to plant the pots .... or should I divide and plant Hosta or Iris in the fall? Thanks again everyone.

Can you tip them on their sides for the winter? For the hosta, the biggest issue could be too much wetness and rotting of the roots.

zooba72 - Spring or fall are the recommended ideal times to transplant perennials. The middle of July is certainly not optimal transplanting season but if you need to move things now, there are ways to minimize the risks of them dying. Things transplanted into containers need to be sheltered/protected from harsh weather so if you have a north-facing or other area where they'll be out of the sun most of the day your chances of having better success are greater.

Sorry to rain on your parade but 12" containers are rather small to grow hosta or iris year-round. I don't grow miniature hostas--most of mine are mid-size--and there wouldn't be sufficient room in a 12" pot for the root ball, let alone enough growing medium to sustain them. That said, I've got smaller hostas growing in larger containers that have come back year after year. Most were grown from seed via winter sowing.

You don't identify what sort of iris you're growing but Iris Siberica/Siberian iris quickly form a very large clump in the ground. Bearded iris don't have massive or deep root systems in my experience but I question whether your pots would provide them with sufficient area in which to thrive.

I'd suggest you post your USDA hardiness zone in your signature/login since that will provide folks with answers to your questions that are likely to more specifically meet your needs.

I have many clumps of Siberian Iris that can be divided and put into the pots. I also have a lot of very large Hosta which also could be divided. I wouldn't try putting anything large in these pots. I'll get something started and then transplant to the ground the following year or so. I'll give it a shot and see what happens. I appreciate the info, Thanks