I got some seeds from a friend late in the season and planted some of them anyway. They came up and are doing pretty well, but still small so I'd like to figure out a way to protect them on my roof garden, where they are now, or possibly bring them indoors to a friend who has sunny windows.

I am in New York City, and the plants are:
1. Telekia Speciosa (a great perennial that now has about 4 sets of leaves, 2-3in tall, so probably not big enough to survive the winter up there.
2. Gallardia - mature plants have sometimes survived on my roof, but not always. These are now about 3 inches tall.
3. Prairie Coneflower - I have never grown this, but got the seeds from a garden in Brooklyn and would also love to keep it alive.

Many thanks for suggestions.

Hardy plants have hardy seedlings.
Do perennials usually survive in whatever sort of planting system you have on your rooftop?

I have plenty of hardy perennials in large containers that sit on the roof itself and those mostly survive (not counting last winter, which was rough).

These seedlings are in a window box attached to the rail right now, and I am certain it will freeze solid. I use the window boxes for annuals and for starting seeds. I have larger containers for the perennials and small shrubs. My large containers are jam packed right now.

Given that the seedlings are still small, how about just transplanting them into the larger volume planters, which you say normally winter over successfully? The plants you list are all extremely hardy (zone 2), given a decent soil volume.

My larger planters are cram-packed with shrubs. I was wondering what they might do indoors but since my apt. is totally dark, I would have to bring them to another location.

@GordonHawk might have some suggestions for you. He lives in Brooklyn and has a lovely roof garden also. Maybe he'll check in here. If you have friends who would be willing to winter over your plants, that would seem to be the best alternative.
You could invest in a grow light to keep the plants happy on a window sill. Watching their progress might chase away the long winter blues!

I would try to give them some cover - like move the window box to a sheltered corner and make some framework over it, then stretch plastic film over that.

BUT a warm, sunny day could cook them or start them growing again in time to die during a freeze.

Maybe make the plastic film only a partial cover - leave lots of vents open at all times. If the goal is only to keep the window box from going below -40F (USDA Zone 2), keeping it out of the wind and up against a wall might be enough.

You might dig out a few of each and give them to a friend, with the understanding that, if all yours die, you'll ask for half of them back.

They sound too small to take cuttings from.

Thanks Sandi...Yes.. Nancy has been by here ... with the roof gardeners group... [ you should make another NYC trip and visit again ] yes to keep them off the roof and out of the wind... that should take care of any zone two plants... the worst foe in roof top overwintering ... is the heat of the late winter sun... heating up the plants enough to start the fluids going up... only to have them freeze again come night fall.. shattering the cell walls of the cells where the fluids had gone.. the worst... that's why I like the foam containers... not only do they keep it cool in the summer ... but it also keeps it cool in the winter.. and doesn't allow that sun I mentioned to heat up the root balls..
I hear it isg etting warmer

I am posting a photo of the seedlings so you can see how tender they are. the window box is attached to the railing so I would have to transplant them. Gordon -- are you saying I could put them inside a Styrofoam cooler for the winter? Would they need light? Every so often I see Styrofoam boxes in the trash on the curb outside supermarkets. Fruit gets shipped in them. I am not sure they are deep enough to hold a flower pot. But if I put them in small pots, how much soil would they need? Would complete darkness be OK? I might be able to find an old cooler somewhere too.

I am out of town the next three weekends, but could keep my eyes out for something that would work.

And thanks to this warm spell, I might get some ripe figs in the next day or two.

Nancy, Gordon has a "walk-in" foam container on the roof in winter. Pretty ingenious set up for winter.

Maybe Gordon was thinking of the foam pots that are available at Home Depot and Lowe's pretty reasonably. I have a couple, they are very light but the walls are about 1/2in thick and have a hard coating. They retain moisture well and also would insulate against the soil freezing much better than a plain plastic pot. (sorry, can't get any pictures right now, it's raining)

Also if you can position your container flat on the roof, and preferably against a south or west facing wall, it will warm up in the daytime and benefit from the heat sink effect of the wall and floor (roof) at night. Protect from the wind at all costs! It's drying as well as cooling.

I've had seedlings of nasturtium stay alive through a Utah (zone 5) winter in a bed against a south facing wall.

Here are the foam pots I have, Nancy. Both from HD, and not expensive (but that was a couple of years ago).

Yes...any foam will help..I build most of my own planters up...with 2" thick foam.. About twice the amount as in the walls of a refrigerator...I have some big treated wood planters also....they have foam lining the inside of the planters...
The picture shows a triangular 2" foam planter with a synthetic stucco coating supporting a shogi screen trellis