I live on the Eastern Plains of Colorado and decided a few years back to try growing figs. My part of the Plains is in Zone 5, and I remember thinking myself quite daring for trying it, but it turns out there's a lot of people growing figs in cold areas.
Growers are helped greatly by the fact that figs have a dormancy period where they need absolutely no light. This means that they can be put in warmer, albeit darker, places (and/or be buried) as a way to survive Winter's chill.
Planting my figs in-ground, and then burying them in Winter was a consideration in my early research. The name I remember was the "Minnesota Tip" : in Fall, you slice in under one side of the root ball and literally tip the tree over into a trench. You then cover the upper with plastic and soil--the trick here being that the ground really won't go too far below freezing and protect your plant.
Space, much more than faith in my ability was the problem here. An in-ground fig, along with the room to lay it horizontally, is (at least for now) a non-starter. Where on earth would I put it? I have a postage stamp sized lot and have literally filled it with plants. I don't have more room without sacrificing something I already grow and love.
Insulating in place was another possible. The problem is that it's simply too cold up here some winters. Insulating in-ground probably doesn't work below Zone 7. I mean, I've had figs nearly die in my attached garage. There's no amount of blankets fiberglass batting to counter the cold we see. Going this route would be a removable shed and supplemental heat.
Not doing that. I landed on container growing as my best strategy. Containers are mobile and can go to the garage (and later the crawlspace) every Fall when outside temps reliably hit 20 degrees or so overnight.
Containers have their own problems, however. Roots. Plants don't know they're in a plastic pot and thus keep trying to send roots out. The roots eventually fill the available space, the plant starts to get sick and then dies.
I've had some luck with grow bags which DO limit root growth naturally, but they're not as mobile as plastic. They wouldn't handle being scooted in out of a crawlspace as well and the guy doing the moving sure appreciates something that holds its shape better!
As with other container-grown plants, the price you'll pay is to either pot up the plant or give them a root trim once they've gone dormant.
I'm potting up this year, but there's a definite upper limit on how big a pot I can to. The crawlspace hole is only so big. I have only so much strength to hoist pots in and out. This means I can't keep up potting up forever, but I just finished the first potting up of my eldest fig, a Chicago Hardy variety. Violet De Bordeaux is not far behind, but she's doing fine where she is right now in her 5 gallon bucket.
I flipped the Chicago Hardy out of its pot. While not root bound yet, there was a solid 1" - 2" chunk of hefty yellow roots running in circles at the bottom of the bucket like matted hair. I cut them off and then started cutting/untangling the roots on the side (matted too, but not as bad).
This can look pretty violent and extreme if you've not done it or seen it done, but don't worry. When a plant is dormant and not under any kind of stress from heat or lack of water, it doesn't hurt anything.
Quick aside, any root trimming on cacti or succulents should be followed by about 24 hours out in the air before replanting to allow the roots to skin over. They are especially susceptible to infection and problems.
The photo below shows the (cleaned up) aftermath.
Next some new soil, packed firmly but not too firmly, and a drink of water. The soil I used was some spent soil from last year's sweet potato towers and probably didn't have much food left in it. I considered adding some fertilizer to the soil, but I decided not to.
Probably pretty low risk, this fig was most definitely dormant, but I didn't want to give even the hint of an incentive to start growing or waking up.
I'll hit it (and the others) with some compost, organic fertilizer, and likely some liquid come Spring wake up.
A nice big breakfast after their winter sleep: liquid to give them something while the compost/organic start to break down into food.
The fig got a moment to bask in the sun on a warm late Fall Saturday afternoon, and then it was back into the garage.
I got a minute to imagine a bigger harvest from a happy plant come the end of next summer.
