Temperature Control for Winter Storage Crops

Courtesy of Wally S., Wally’s Urban Market Garden, Saskatoon SK

More and more consumers go to year round farmers markets so they can know where their food comes from, even in winter. What they find at my stand are storage crops, like beets, carrots and potatoes.

Part of the challenge of year round marketing of produce in cold weather winters is keeping your storage vegetables in good physical condition for several months. Just as in the summer, I take SPIN’s high road by using a cooler. Keeping it at the right storage temperature is key. My cooler is on average around 35 F, or few degrees above freezing celsius. It’s in my garage, along with a work area for prepping produce. I keep it in my garage, which is heated with a small plug in radiant space heater. The thermostat is set to 50 F.

A few nights ago it was -35 Celsius overnight. Just made a celsius to fahrenheit calculation and ironically this is the temperature where the two scales converge: -35 C is the same as -35 F. So I have to deal with the outdoor temperature, the garage temperature and cooler temperature. The heater keeps the garage at 50 F., but the question is how do I keep the cooler at the desired temperature? I find just partially opening the cooler door allows air to seep in from the garage, when it is very cold outside. When temperatures outside get warmer, I can shut off the heater for certain periods of time and close the door for the cooler. Right now the cooler temperature is 34 F, which is about optimal. The aim is to keep it above freezing, and below 40 F.

SF photo Wally temp2


This is not a high tech method for sure, but it works, as long as I keep an eye on things happening inside and outside. So you don’t need an elaborate setup to keep your farm stand stocked with the staples that keep your customers coming, and your cash flowing,  when the snow is flying.


Video on Building a Cooler Using the Coolbot

Courtesy of Paul, H., Victory Garden Vegetables, Cobourg, ON

I use the CoolBot, and this is the second walk-in cooler I’ve built using a CoolBot and air conditioner. Last summer I made a 20-minute video about its construction and posted it to our website:

I have yet to tabulate the cost figures. What I can say for sure is that this size works great for us right now, and in fact we are still hardly using even a quarter of it. However we still only have about 5000 square feet of land in cultivation right now, so hopefully our use of the cooler will change as we continue expanding!

As far as time expenditure goes, I would very roughly say it probably took 6-8 full days to get built into a usable state, plus another day here and there spent on aesthetics and touch-ups.

DIY Coolbot Walk-in Cooler Tips

Courtesy of Jame K., Virtually Green, San Francisco, CA

Here’s a few quick thoughts about walkin cooler design, largely based on what my appropriate technology group used to recommend for village small-scale DIY walkin cooler systems.  We didn’t have the Coolbot at the time though:  it’s a great alternative to commercial refrigeration units.

Here’s a link to a Canada Plan Service document that lays out some of the basics for designing and building a walkin cooler.


The Coolbot retrofit of window air conditioners is a reliable solution, but do follow the Coolbot suggestions for the best air conditioner unit.  I know someone who went cheap and regretted it immediately.  I also recommend that you get two air conditioners rather than one, so you have redundancy in this critical component of the walkin cooler.  You really don’t want to find yourself with a failed air conditioner and a cooler full of spoiled produce.  If one of the units goes down the other can pick up the extra load until you can replace the failed unit.

Another thing.  Use a strip door to keep cool air in when you’re entering and exiting the cooler.  These are thick wide plastic strips that hang vertically from the top of the door to the floor and that overlap each other horizontally.  You push through them to enter and exit.  These can radically reduce the loss of cool air when moving quantities of produce in and out.

The size of a walkin cooler is based upon peak use, in other words the moments in the harvest cycle when you have the most produce needing cool storage.  Use the dimensions of your standard sizes of storage containers:  bins, boxes, tubs, etc.  If you’re doing the routine crop planning for SPIN beds then you should be able to estimate the maximum volume of your various harvested crops needing container storage in your walkin cooler during your harvest weeks.  Leaving 50% of the interior volume for aisles and air circulation is a good rule of thumb, which can also in emergencies temporarily handle extra produce volume if needed.

You’ll likely be using pallets or shelves for your containers, so remember to leave room for maneuvering dollies and lift-trucks in and out of the walkin cooler.  Shelves that can be adapted to different dimension containers allow you to flexibly respond to changes in the quantities of your harvests.  Also with shelves remember the work safety, ergonomics and back strain issues of lifting containers on and off high shelves.

You need to have the air inside the cooler circulating freely to avoid hot or cold spots or major differences in humidity in the horizontal and vertical volume of the cooler. Set the Coolbot air conditioners to optimize their effects on air circulation.

One thing you don’t want inside a walkin cooler is condensation problems, which can lead to mold and mildew that can affect produce quality.  You want high humidity to avoid dessication and wilting of produce, but not so high that water condenses on surfaces.  Mount a couple digital dual humidity/temperature meters inside your walkin cooler to monitor humidity and temperature at different horizontal and vertical locations.  You can use these to monitor and better calibrate the performance of your air conditioners as well.  I recommend buying ones with NIST certification to ensure that they will perform as advertised and also to satisfy any food safety regs or or insurance concerning produce storage.  Here’s an example of what I have in mind:  http://www.calright.com/products/prod_id/1794/