They're perennials, and yes you can - as long as you provide suitable cultural conditions.

Al

I saved two asparagus ferns this past winter in my unheated (attached, partially underground) garage. I'd say it stays somewhere between 40 and 50 in there all winter. Just stuck them in the back (as far from the doors as possible) with little to no watering. So far, so good. Just repotted them 2 weeks ago and they both look green and healthy. This was an experiment for me since I had not done it before. I figured if it worked - great ...free plants next spring, if not I would be at the same place I usually am, replacing such plants.

Thanks! I'm gona try that. Why lose these plants if i can keep them!

The ivy though I need to caution that it may be infested in spider mites! They absolutely love English Ivy, and often grow into huge uncontrollable numbers inside! My family has had large collections of indoor plants in the past, to loose them all when some "ivy" is brought in, either from a garden or from a store...

English Ivy grows all over outside here in my Zone 6... (Greater Toronto Area / Southern Ontario) Once established it threatens to take over entire houses, becomes rather invasive actually! But I know before it gets firmly established, it does take some care to overwinter it outside. Probably want to plant it in the ground and mulch it well... Or perhaps pot it up in a styrofoam cooler once the temps get cold and it goes dormant.

English Ivy is perfectly outdoor hardy in your zone and much colder. II totally agree with the previous comment about the spider mites. This plant much prefers the outdoors than the warm inside environment, where spider mites are able to explode in population.

Asparagus fern is planted outside in warmer climates (as an ornamental), where it may be top killed in a freeze, but regrows quickly from the roots. It will be very easy for you to protect it over your winters in a coolish location.