I have moved to Zone 5---a vastly different winter exprience from my previous zone 8 location.
I was able to plant most of the species tulips in ground, but snow & below freezing temps arrived earlier than expected. Needless to say, the ground is frozen so the alternative was to plant the remaining tulip bulbs into containers & store somewhere safe until we're through with the more extreme temps.
My question is regarding winter protection. Placing them in the garage is one option, but I was curious if anyone has placed container-planted hardy bulbs into thick styrofoam boxes (with lids) outside.
With limited space in the garage, I thought the enclosed styrofoam boxes might work outside under the potting bench, but I'm not willing to experiment unless there is a chance of success.
Any suggestions welcome; thank you kindly for your responses.

Pile some leaves over the pots and then pile snow on them. I would worry about rotting and molding in a sealed styrofoam box. Look for a place that the ground hasn't frozen. I've planted tulips at this time of year, and I'm almost in Zone 3.

Thanks Rubi!
Unfortunately, I don't have leaves available to provide for additional insulation.
I wasn't intending to keep the styrofoam boxes tightly shut, but provide a bit of airspace by propping the lid about 1/4 - 1/2". The box would be placed under the potting bench (next to the house) & I'd be checking the containers inside them weekly. I did this previously in zone 8 when we had a drop in temperature. However, dealing with persistent lows in the teens is different than the 3 days of upper 20's, so I wasn't certain about whether the soil in the containers would freeze solid while in a styrofoam box, with the lid slightly raised.
If the soil wasn't frozen in my raised beds, I'd dig the containers into one.

I will try an experiment with the styrofoam box by placing a container of soil (minus any bulbs), to see if the soil freezes. These species tulip bulbs are hardy to Zone 4/5 & I'd rather not sacrifice them.
Thanks again for your timely response - very much appreciated!

When does your weather start to warm in the spring? I wonder if you could hold the unplanted bulbs in a produce drawer in your refrigerator and plant early spring.

How about, place pots on ground, under the bench, and overturn the styrofoam on top of them? Then you get some ground warmth and, it won't be totally sealed to airflow. But.. some critters might find this nce refrigerated treat to eat.
Once you prop the lid open, are you really gaining much (temperature moderation)? It's not as if the pots generate their own heat- just that you're avoding the nightly swing to very cold, right? What if you have string of cold weather?

And, do you need much? Hardy to zone 3.

I have no experience to back this up but wish you luck.

How many?
Theoretically, depending how deeply frozen your ground is, you could take a grub hoe, or ice breaker and break through the frozen ground.
You can then, actually peal off large chunks of frozne turf like pealing solidied grease from soup.

If they are supposed to be planted six or so inches deep, do so in the soft under soil, put the frozen cap back on.
I did this planting roses in frozen soil, but I then covered them with leaves and if I remember right pressed paper caps on some.
Just a thought.

NMoasis: my preference is to have them blooming early spring, so they need to be planted now.

SallyG: I thought about placing the styrofoam box over the container-planted bulbs, but the ground is frozen & it would be more difficult to check the containers to ensure they don't freeze. We will be getting snow through February, so that's an additional hindrance regarding access.

RpR: great idea, but the ground is frozen & I'm inclined at this point to place all the containers in the garage (not insulated) & bring them out on days when temperatures climb above freezing.

Thank you all for your contributions - it's quite a challenge when your zone differs radically from where your previous residence was located. As usual, there are pros & cons!

Your goal should never be to keep the tulip bulbs above freezing (32°F). This is the worst thing you can do. This is when rot happens if the soil is too wet. Wet soil that is frozen becomes dry in the eyes bulb pathogens, so rot doesn't occur. Additionally, if the soil never freezes, temperature fluctuations increase, because there is no water phase change (solid to liquid or vice versa) that absorbs or releases an incredible amount of heat to change phases without changing temperature. Your goal should be to moderate the temperature and reduce temperature swings, whatever temperature you are at.

Here in zone 4 tulips never dies because ground temps are too low. Our soil freezes down at least 2.5ft down, and often 3.5ft. Tulips are in the ground with temps well below freezing, and don't freeze themselves. See the chart here. Note that Temps are in Celsius, not Fahrenheit!

https://journals.ashs.org/hort...

A couple of years ago, near here, the DOT soil temperature monitoring station had the frostline 84" deep. Tulips freeze solid every year here. I bought my house in 2003, and I have tulips from the original owner that are still blooming every year. I've never touched them once. Last year it was -38F in January, without much snowcover at the time, and the tulips were fine; even the ones I planted on Dec. 5th with the frost about 2" deep. Tulips want to freeze. That's why they aren't perennial in the South.

I can't comment on potted tulips, but in general, they need to be cold and stay cold.

Update -- Regarding the tulips cited in my original post:
Those planted in-ground, emerged.
Those planted in small plastic containers & were stored in an un-insulated garage all emerged.
Those planted in a 24" x 24" concrete container outdoors, froze & turned to mush.
So much for tulips needing a freeze. What they do require is being subjected to an extended period of cold.

Clearly, planting in-ground & planting in a large, thick-walled container subjected to outside weather conditions provide different results. I'm in zone 5 with normal "winter" lows in the teens plus snow for extended periods of time.
Thus, the ideal situation is to plant them in-ground. But -- if you run out of time or winter arrives sooner than expected, my recommendation is to store container-potted tulips in an unheated garage.

Tulips need the cold, but they don't like being wet and cold. It's possible the concrete containers held onto too much moisture for their liking. Were there drainage holes?

Yes, in fact 4 large (1") drainage holes; soil in the container has extremely fast drainage which I have used with bulbs historically -- over the past 40+ years. These tulips were species tulips--not hybrids--& typically can take pretty harsh conditions.
Yes, they need cold, but freezing is another thing. Bulbs planted in-ground have an insular factor not present in a container, even one as large as I used.
My original question was where to place the leftover bulbs since the ground had already frozen. Thus, they were planted in several 12 & 15" plastic pots, with the rest being planted into a 24" x 24" concrete pot.
The concrete pot was outside & subject to the weather; the plastic pots went into the garage & never experienced freezing. The concrete pot had a simple mulch of ground-up dried leaves over the top as did my other perennials. Thankfully, I only lost the bulbs in the concrete pot....
So, this was an experiment of sorts. I will continue to plant in-ground but sometimes winter arrives early & with a vengeance. In that case the extras will be planted in pots which I can overwinter in the garage, since that worked quite well.