A very popular question with growers in zones 8A and colder is “How do I protect my in ground trees in the winter?” Fig trees are sub-tropical trees from the Mediterranean, the Middle East, and North Africa – all warm places. For those of us in the cold north (we are in zone 7A) we must take steps to keep our figs warm in the winter or accept that some years trees will be wiped out to the ground level. There are countless methods to winterize figs ranging from planting against a sunny south facing wall to covering and heating. Our method is a variation on covering and heating, other methods can be found on the forums including OurFigs.com.
Our method started with this post. We plan to trim my trees back to about 4′ posts each year. This let’s us have several varieties in ground and avoids a very large wrapped tree in our yard.
I built 14 of these fig houses using plywood and 1/2″ foam board insulation. First here is what the end result looks like.
The goal is to make a semi-permanent (reusable for a few years) structure that will protect the trees from the wind and keep some heat in. I cut several 8″ wide pieces (12 per 4X8 sheet of plywood) at one time. Each piece of plywood has a slightly smaller piece of 1/2″ foam glued to the inside using construction adhesive. The sides are then screwed together with deck screws and a 10″X10″ top is attached with deck screws.
I painted the fig houses the same color as our house/shed.
The figs are wrapped with burlap (though I omitted this for some of them) then with a Frost King 12′ pipe heating cable. The cable warms up when the temperature drops near freezing using a built in thermostat. Each house is connected to an extension cord. For the houses near each other they are connected in series with a 3-way adapter in each one (only a two way adapter is required, but I couldn’t find any of those) so that the houses can be connected by short cords.
The houses are anchored to the ground using ground anchors. For the free standing houses all four sides are anchored; for the houses against a trellis wire two sides are anchored. Without anchors they would blow over in heavy winds.
Here is the final result. So far the fig houses and heaters have performed well in the cold. We experienced 4 F with 20 mph winds and a temperature sensor stuck to the inside wall of the fig house did not go below 25.4F. Also, the high temperatures have not been bad. Even for the houses in direct sun the temperature does not get much more than 10 degrees above the air temperature. The final test will be in spring when I unwrap them.
Follow Up (April 2019):
Now that the freezing temperatures seem to be over I uncovered my trees. The results were interesting. I covered 14 trees in this manner, 11 of them look like they spent the winter in California (nice green buds and even a couple of brebas) while 3 were cold damaged almost all the way to the ground (they were dry and brittle and broke easily). I assume there is a good chance they will regrow, but lost almost all the above ground growth. Two of the three failures were the smallest diameter of the ones I covered, but the third, a Smith, was an average size. The three damaged varieties were Nero 600M, Ge Neri, and Smith.
I monitored the temperature and humidity in one of the enclosures, and the temperature did not get below 28.5. This was the enclosure for one of the plants that looks great. I could confirm that the three damaged ones did have power (the cords light up) when I was dissembling them.
So it is a bit of mystery why 3 did so poorly while the rest did great, but I am guessing it was some sort of failure of the heating elements or bad placement of the thermostats that turn on the heat. They are hard to test since they produce minimal heat, and only turn on when it gets close to freezing.
On the bright side there was no sign of mold on any of them. Despite allowing them to remain in the enclosures till what I hope is after the last frost, and despite the humidity being high all winter in the enclosure I monitored, there was no sign of mold.
Overall I really like this method and plan to keep using it in future winters, and even building some more. They take some time to construct, but once built they are easy to set up (3 hours or so to get them all connected) and about an hour to take them apart and store them for the summer.
Here are some of the healthy ones:
These were some of the damaged ones: