Overwintering Globemaster Allium?

I bought some globemasters earlier this year and now that I am starting my fall planting I notice that they are only hardy to zone 5/6 and I am in zone 4. Could I pot them up and keep them in the cold basement? Any suggestions?

Nevermind. Apparently different sites claim different hardiness, I think I will just have to figure this one out the hard way. :)

You can pot them up. The cold basement ought to give them enough chill factor without freezing them. Keep them on the dry side while they are dormant.

Here in Scotland which is way much cooler in summer than most USA states, add to that, a very short summer growing season, much rain and where I live and add to that strong gales that come straight off the sea.
The point I want to make is, every year I have to winter / shelter or pot up and take indoors, or just add thick mulch depending on the plants I am trying to care for.
I would say as I get older, this type of prep is a burden rather than enjoyment it was many years ago,
I would however not stop trying to save my more tender plants (tender for my area) so IF you want to grow some plants that are a wee bit tender in your climate, it's wonderful and challenging and time consuming BUT WELL WORTH THE TROUBLE. You learn a lot by widening your skills and also, you get the pleasure of seeing plants / flowers that makes you appreciate just how wonderful nature is with a little help from us gardeners.

Do as Diana has recommended, just Don't put the bulbs into pots way too large, I would pot the bulbs individually, pots too large mean more soil / compost around the bottom of the bulbs, and this can cause rot problems IF you are a bit inclined to over water, larger pots need a bit more water.
As the bulbs settle into the pots, after a few months, there is nothing to stop you from emptying the pot onto your hand and just a little check on the bulbs, see they are still firm BUT, don't rub, shake or drop the soil or you might disturb any new roots. all your trying to do is keep the plant alive but only just.
Hope it all works out for you and you get much enjoyment from your extra care, every year putting your garden to bed is just as exciting as you get to look close at what you have acheived from the season past.
Kindest regards. WeeNel.

Allium 'Globemaster' is hardy here in zone 3, despite spotty snow cover and chinooks. You shouldn't have to worry particularly. If there's any lesson in it, it's that zone ratings are generally untrustworthy, and only actual growing experience counts.

Thanks for all the advice! I decided to try it both ways and compare the results. Next spring certainly will be interesting!

I would think they would be ok. We had a winter much colder than our typical zone 6 and they didn't miss a beat. I'd mulch them well and not worry about it.