Hmm. The leaves look serrated until you enlarge the photo by clicking on it.
Doesn't this REALLY look like a Yucca plant? (I see that some common names for Yucca include Spanish Dagger and Spanish Bayonet
The one I have is hardy outdoors here (and winter lows can get as low as -5Ã‚ÂºF
), but there are a number of different species, I believe, so I can't say if yours would be. How cold does it get in your garden? Oh! It'll also depend on whether it's in the ground or potted as potted roots can freeze without protection.
If the hardiness of your plant is borderline in your area, and you decide to grow it outside, it would be best to plant it in the ground this spring so the plant will have plenty of time to establish roots. You could provide additional protection in the winter with good mulch and perhaps a burlap wrap.