Fig trees need to be buried in order to survive the winter in northern climates. This tree is about 15 years old, so it knows the routine. I'm in southern Michigan, so the winters between the lakes can be brutal at times. The objective of burying it is to protect it from the freeze/thaw cycles that happen around here. Keeping it at a relatively constant temperature, even if frozen, will protect it from damage.
Step 1: When to Bury a Fig Tree.
You need to wait until a good frost causes the leaves to drop. This usually happens just before Halloween, so I like to bury them on that date. Your neighbors will think you are digging a grave. Figs will still be on the tree, but they can be easily knocked off by hand.
Step 2: Tie the Tree Up
Take a thin nylon rope or cord and tie an end to the base of a large branch. I tried using hemp twine, but it will break down and make it difficult to extract the tree in the spring.
Slowly walk around the tree, capturing the branches as you move higher. Branches are incredibly flexible, so bind it tight as you advance up the tree.
Tie it off with a simple square knot.
Step 3: Dig a Trench
The trench needs to be long enough and wide enough for the tree to lay into. The top is more critical to get all the way into the trench. Dig down at least 18"-20". The frost line is much deeper around here, so it will stay frozen in the dirt.
Step 4: Dig Around the Front and Back, But Not the Sides
The objective is to lay the tree down without severing all the roots. when you dig, put the shovel in so you don't cut all of the roots. Undercut the front - facing the trench - so the root ball will pivot into the trench.
Step 5: Lay the Tree Into the Trench
Tackle it from the back and push it into the trench.
Step 6: Arrange the Top
Make sure the tops are solidly into the bottom of the trench.
Step 7: Cover With Porous Plastic or Fabric
I reuse the same cheap plastic tarp every year. Note the slits and holes I cut in the tarp. You want to keep the dirt at bay while letting air and water circulate. if you don't, there will be mold all over the branches when you dig it back out.
I put some leaves on the root ball to keep the roots moist.
Step 8: Cover With Dirt
Say some kind words to the tree, then cover everything loosely with dirt. Don't pack the dirt or walk on it. You should have enough with what you shoveled out of the trench.
Step 9: Cover With Leaves
Gather leaves from your yard (or the neighbor's yard) and cover everything at least a foot deep. I use oak and maple leaves - avoid walnut leaves.
Step 10: Pack the Leaves to Keep Them From Blowing Away
The nice thing about Halloween is people buy straw bales for decoration, and you can usually get them for free afterwards. I weigh the leaves down with several bales and anything else I can find in the garden.
The tires are what I plant potatoes in, and have holes in the sidewall to prevent water collection.
Step 11: That's It!
Here are some pictures of my other, smaller tree. I wait until Mother's Day to dig the trees back out. I will detail that in another Instructable.
Enjoy your winter!
January, 2018 update: I finally published the follow-up called Un-Bury a Fig Tree!