By Steven Biggs

Overwinter Figs on Balconies

I recently spoke with fig grower who grows figs on a condo balcony in Toronto...a small condo balcony where winters are cold!

I was so impressed with his creative approach to overwintering figs that I asked if I could share it. Here it is below, in his words.

I give my thanks to this fig pig (who prefers to remain unnamed) for sharing his experience!

Re: Overwinter Figs Where You Think You Can't: Fig Overwintering for Condos/Apartments

Hi Steve,

I read the excerpt from your book Grow Figs Where You Think You Can't about overwintering figs, and I applied the basic principles for a condo/apartment situation. I grow figs on my condo balcony in Toronto but have no yard (so no ability to earth-insulate), and no unheated garage or cold, dark room either.

My first year I had only 1 fig tree (about 2' tall). I took a rectangular wood planter box (approx. 3' x 1' internal) and lined it with Styrofoam (and cut out a Styrofoam lid too) to serve as an insulated container. I placed my dormant fig inside.

Since I planned to store it outside on my balcony over winter, I considered various heat source options (e.g. seedling heat mat, light bulb, coffee warmer, etc.). I ended up buying a small 7.5 watt flat oval fish bowl heater (meant to go under aquarium gravel), which I placed into a mason jar full of water that I put inside the insulated wood planter.

The aquarium heater is my version of a DIY water radiator. It has the added benefit of the water jar acting as a thermal mass for heat energy storage and temperature regulation. That is, the water is slow to warm and slow to cool, so temperature changes are gradual and moderated. The other advantages of fish tank heaters are that they are 100% waterproof (so they're safe for wet environments) and they're inexpensive too. A seedling mat was my initial choice but they were far more expensive, plus they lack the inherent thermal mass storage and regulation properties of a water radiator.

The flat plasticized fish bowl heater I used the first year provides continuous heat (no thermostat) and it basically kept the water above freezing and about +5°C to +10°C above the ambient air temperature. Only on the coldest of Toronto nights (e.g. those -20°C nights) did it get a bit too cold, and I needed to wrap the whole container in extra blankets to add insulation.

Plastic cooler with dormant fig and heater.

The next year I bought 3 more figs and needed a larger container so I bought the largest picnic cooler I could find, a marine cooler intended for boaters. I also upgraded to a higher wattage glass fish tank heater with a built-in thermostat. I supplemented it with a thermostat controlled AC plug switch, a ThermoCube TC-3, which turns on AC power to the heater around 2°C ambient air temperature and turns it off around 7°C.

I managed to fit all 4 figs in the large cooler and placed the fish tank heater in a large glass jar filled with water, the power cord running out the top. I taped shut the glass jar top to prevent water splashing out when jostled. I set the fish tank heater thermostat to the lowest level but when paired with the ThermoCube TC-3, the ThermoCube on\off temperatures are the primary thermostat.

Because I needed to lay my figs flat on their side, to prevent dirt from falling out I wrapped the figs in scraps of old cotton bed sheets. Initially I tried plastic but I was concerned about the lack of air flow and felt it trapped too much moisture.

For peace of mind, I also bought an electronic wireless thermometer (ThermoPro, $20) which includes a hygrometer to measure humidity. The sensor component was placed inside the fig cooler and the display screen kept indoors for easy monitoring. That kept me from constantly worrying and wondering what was happening with my figs.

The first year's fish bowl heater was 7.5w and just $13 (Hydor 7.5w Slim Heater for Mini-Aquariums and Bowls up to 5 gal). The second fish tank heater was 200w and just $20 (Pawfly HT-2200 Submersible Aquarium Heater 200W with Thermometer and Suction Cup, 50 gallon).

In my experience, the 7.5w heater was slightly undersized for my DIY insulated wood planter (but it would depend on how insulated the container is and the 200w is certainly overkill even for the larger cooler since the cooler is well insulated. I would suggest anything above 25w would probably work, depending on water jar and container size, and on insulation level.

Having more power is fine as long as you have a thermostat-controlled AC switch such as the ThermoCube to prevent over warming. Most fish tank heaters are intended to maintain water temperature above normal room temperature, and the thermostat minimum on the 200w heater was 16°C. Even with the 7.5w heater and without the ThermoCube, I found I was unplugging it manually on days when the ambient outdoor air temperature was above freezing, and it stayed mostly unplugged beginning early spring.

Bottom line: using a ThermoCube removes the guesswork and the risk of over warming.

Also, since picnic coolers are quite well sealed when the lid is closed, I would recommend leaving the lid ajar to prevent excessive humidity build up and to provide more air flow. Since the fish tank heater is submerged in water, that might also provide an additional source of humidity depending on how well sealed the water container is.

I would recommend only a very light watering before placing the dormant figs inside the cooler as the humidity can remain high in such an enclosed space. In my case, I watered my 4 figs thoroughly before they went into the cooler and they were still moist months later when I took them out in the spring.

Anyway, that's my fig overwintering technique for condo living. I hope this helps others in similar circumstances. It's very satisfying to be able to grow (and overwinter) figs where I thought I couldn't, on a balcony in an urban northern climate. Thanks for the inspiration!