Monday, January 13, 2014

Overwintering Experiment – Winter 2013

Searching on the internet there is a multitude of overwintering beehives. Most of it is completely inappropriate to harsh Canadian winters. As a new beekeeper I was rather confused and worried about overwintering options –I didn’t want to lose more bees then I ought to. In addition to these difficulties this autumn wreaked havoc; the goldenrod bloom never came for their winter stores, and due to the unusually warm autumn any honey left on for winter stores was quickly used up. By the time this was realized, it was becoming too cold for syrup so emergency dry sugar feeding was the only option.

The Biology andManagement of Colonies in Winter, by Adony Melathopoulos contains a great deal of information regarding the overwintering of bees in very cold climate (Beaverlodge – Alberta, coincidently where my bees genetics began with work by TI Szabo). 

Michael Palmer has some great advice on wintering colonies on his presentation Keeping Bees inFrozen North America.
But, all this information was “after the fact” for me so I setup a short experiment. All the hives save one very small colony (late swarm catch) and one large colony (best producer) were roughly similar sized clusters. All had very little honey left and are surviving off emergency granulated sugar feeding.

Screen Bottom Board vs. Solid Bottom Board

It is very easy to imagine to ourselves that bees get cold. It is another example of how we as humans assume that because we are cold, that the bees are as well. This is a completely false notion. Bees are affected by temperature in the sense that they must keep their cluster at a constant 32-36 degrees Celsius. This in turn affects their metabolic rate, and how much they need to consume in calories to produce that heat. At 5 degrees Celsius bees use the least amount of honey, steadily increasing the cold it gets. Likewise, any warmer will trigger brood rearing which will also use up a great amount of honey.  
I placed three colonies on screen bottom boards, and the rest on solid to see if the open SBB would have a negative effect on those hives. In late December I had checked on them. The SBB did not seem to contribute any negative aspects on any of the three hives. Conversely, the ones with SBB looked to be drier. The solid bottom boards however had remnants of newspaper, sugar, and dead bees that had grown mouldy, whereas the same detritus found on the SBB hives was not mouldy. This indicates that although slanted forward to minimize moisture in the hive it was still an issue.
They are currently still on SBB, and Solid Bottom boards as they were, I do not feel that it affects the hives one way or the other.

Wrapped vs Unwrapped

Wrapping with tar paper (roofing felt), worth the effort? Not initially part of my experiment, but after running out of light while wrapping I had to call it quits, and consequently left some hives unwrapped. I went with it to observe possible differences. Tar paper gives a moderate amount of protection to the hive, prevents some drafts, but is primarily for solar gain.
When I went to check the hives in late December, we had above zero temperatures. I opened the entrance reducers to clean out debris, and dead bees from the bottom boards. I was surprised to see that hives with tar paper (with or without solid bottom boards) were able to take a cleansing flight. Those without tar paper did not. It goes without saying that cleansing flights are very important for the health of the colony, those without tar paper were later wrapped in hopes that they would get a cleansing flight the next warm day –which they did.

On Entrance Reducers

I am not bold enough as of yet to completely remove entrance reducers from overwintering colonies. Michael Palmer uses 1/4inch hardware cloth (wire mesh), to protect from mice entering the hives, but is otherwise wide open. What I can tell you is use the largest opening. Ventilation is the most important aspect of overwinter, and condensation equals dead outs. There is noticeably more moisture in hives using the smallest entrance reducer opening. In addition turn the entrance reducer upside down, and face the entrance up. This was a tip given to me by a friend. It prevents the entrance from getting clogged up from dead bees, which in turn prevents them from taking a cleansing flight.

It is currently January 13, 2014. All hives are currently still alive. This page will be updated as the experiment of SBB vs Solid continues, and if any long term effects are observed. All hives save one, are clustered at the top super eating granulated sugar. Fingers crossed.


  1. Regarding screened bottom boards (SBB), what was your setup for upper ventilation? Here in Iowa, we get bitterly cold -10 to -20's F up to 50's and 60's F during the winter months.
    These large fluctuations in winter temps make beekeeping challenging to say the least.
    I find using SBB's with the inner cover flipped in the winter position provides an upper entrance as well as an exit for any condensation via a chimney effect. I use 2" pink Styrofoam on top as well.
    I have also gone one step further by building what I call a ventilation shim: a 2" high board with 1/2" holes drilled on each side (3 holes on the long sides and 2 on shorter ones spaced evenly). The holes are covered with window screen to keep ants and wax moths out in the summer.
    I also wrap the hives, but gave up on the hassle of roofing paper years ago. Instead, I use heavy duty landscape fabric which I wrap twice. A few staples to secure it, and one just below the upper entrance, and I'm done. SO much easier!
    I leave the shims on all year long. My bees stay dry in winter and work less to stay cool in summer. In fact, I no longer see any mold in my hives.

    Dennis K.

  2. Here in Ontario the snow usually gets up high enough (note should buy snow shoes for winter) it will insulate them. Bees do not commonly die cold, but damp will kill them in a heart beat. Mine always have a vented inner cover. I do experience losses, and probably will this spring due to a warm autumn.