Although naturally hardy only in U.S. Department of Agriculture plant hardiness zones 7 through 11, figs (Ficus carica) can survive in USDA zones 4 through 6 with protection. Usually the trees will begin to experience damage at 10 degrees Fahrenheit and suffer the death of all their top growth at 0 degrees F. USDA zone 5, with its minimum temperature of minus 20 degrees F, and USDA zone 6, with its low of minus 10 degrees F, both push the limits of what figs can endure. It is important, therefore, to choose your cultivars carefully.
Choose a Hardy Fig Cultivar
The cultivars most likely to survive winters under such frigid conditions include:
“Chicago Hardy:” USDA zones 5 through 10
"Brown Turkey:" USDA zones 5 through 9
"Celeste:" USDA zones 6 through 9
All of these trees produce pear-shaped fruits in the small to medium size range -- purple for "Chicago Hardy" and violet-brown for the other two cultivars -- with red flesh. In warm climates "Chicago Hardy" and "Brown Turkey" can make two crops a year, the breba or first crop on old wood in early summer and a second on new wood in early autumn. "Celeste" usually makes only one crop in mid-summer and the other two cultivars may not always turn out a breba harvest in the north, but are more likely to do so if their top growth is protected over winter.
"Chicago Hardy" may survive uncovered to at least USDA zone 6 by dying down to the ground during winter and sending up new sprouts in spring. By so doing, however, the tree sacrifices its breba crop. For a more complete harvest, shield all of the cultivars as much as possible over winter to prevent such drastic die-back.
Protect a Container Fig in Winter
One of the easiest ways to protect a fig tree in the north is to plant it in a large container with drainage holes, such as a 16-inch diameter pot, preferably one atop castors to make it easy to move. In autumn, after several light frosts have caused your tree to drop its leaves, wheel it into a dark outbuilding -- such as an unheated attached garage -- where the temperature remains between 27 and 45 degrees F. Keep the fig dark, with its soil barely damp, during winter and early spring to preserve its dormancy.
Protect an In-Ground Fig in Winter
To protect a fig growing in the ground, you either will need to surround it with insulating materials or bury it, after it has lost its leaves in late autumn. Whichever method you use, swab the blades of your pruning shears with rubbing alcohol to sterilize them, trim the tree back to 4 to 6 feet in height and tie all its branches upward close to the trunk with heavy garden twine.
For the "surrounding" option, construct a vertical cylinder around the tree with hardware cloth, chicken wire or snow fence. Make that cylinder at least 6 inches taller than the tree and 12 inches wider than it on each side. Then stuff the open space between the fig and the cylinder with straw or dead leaves and top it with a tarp. Alternatively, tie fiberglass insulation – paper side out – or old carpet around the fig, covering that layer with tar paper and capping the bundle with an inverted flower pot.
To bury the tree, dig a trench beside it, beginning that trench 1 foot away from the trunk and making it 2 feet deep and as long as the tree’s height. Then move to the other side of the tree and use a spade to cut the roots on that side, about 1 foot away from the trunk. After tipping the tree into the trench and packing a mulch such as dead leaves around it, cover the excavation with plywood and a tarp.
Uncover a Fig Tree in Spring
Two or three weeks in advance of spring's final frost, wheel a potted fig tree outdoors again or uncover an in-ground one. Set a potted tree in the shade for a few days before moving it gradually into stronger light.
A fig that has wintered in a trench will need to be returned to its original vertical position and its trench filled in with soil. Tie it to a sturdy 5- or 6-foot stake to hold it in place while it becomes reestablished.
The tree usually won't be bothered by light spring frosts while it is still dormant. Once it begins to leaf out, however, cover it if frost is predicted.