In a previous post, Moisture Quilts vs Hard Insulation, I argued that hard insulation over the inner cover is a cheap and easy way to keep a hive relatively warm and dry over the winter. And it is. I used hard insulation in my hives for several winters with no problems. Even though I’ve since switched to moisture quilts, this year — as in a couple of weeks ago — I set up two of my five hives with hard insulation as a demonstration that I planned to report in on over the winter. But I pulled the plug on that experiment because I discovered moldy frames in the top boxes of those two hives yesterday.

I could have left the hives alone because some slightly moldy frames aren’t the end of the world. I’ve seen bees consume moldier honey than this and live to tell the tale. There’s also a fair chance I may have found similar frames in my moisture quilted hives if I’d looked. The problem might not be with the hard insulation.

All my hives consists of three deeps. Ideally the bees are clustered in the bottom deep with honey in the second deep above them as well as in the third deep on top. Which seems to be the case for me. Here’s a photo of what I saw looking down through the third deep:

A cluster of bees deep down in the hive with two heavy deeps of honey on top to keep them alive all winter is exactly what I like to see. Except that the top deep isn’t entirely full of honey (though I’d say the bees still have plenty of honey for the winter). I fed my bees sugar syrup until it was too cold for them to take any more of it, which isn’t always the smartest thing to do because even though the bees are able to store the syrup, they may not have time to cure it (evaporate most of the water from it) and cap it like they would with honey during warmer weather. Subsequently, as in my case, the ole beekeeper discovers a top third deep filled mostly with uncapped syrup — or as we like to say in the real world, moisture. Not enough moisture to drip down on the bees and kill them, but enough to dampen the frames and allow some mold to grow.

Mold doesn’t usually grow on frames full of bees that are constantly cleaning everything they touch. But the bees are clustered down in the bottom of the hive now. That’s usually what they do as the weather turns cold.^† So I have no bees to clean up all that mold.

†I’ve heard from some beekeepers who say the bees start the winter at the top of the hive and work their way to the bottom. I’ve never seen that happen with my bees in my local climate.

So… I have bees clustered deep down in the hive where they should be, but the top box is full of unattended and uncapped sugar syrup that has released moisture and caused a thin layer of mold to grow over all the comb. (That’s my story and I’m sticking to it.) It’s probably not enough mold or moisture to hurt the bees. But do I want to risk it getting worse? No. The hard insulation over the inner cover will probably do an adequate job at keeping the inside of the hive dry. But I know from from personal experience that a moisture quilt will keep it even dryer.

Preferring to play it safe than sorry, I removed the hard insulation and added a rim. Then I dropped on a moisture quilt.

I topped it off with a standard telescoping top cover.

I don’t think the thin layer of mold over the comb in the top deep would have been an issue if the bees had had time to cure and cap the syrup before it got too cold. There’s also a chance that hard insulation doesn’t work as well where I now keep my bees. I had a problem with moisture — a big problem — when my hives were set up in a foggy, swampy, damp area close to the ocean. Here’s a sample of how swampy my old beeyard got at times:

My new location isn’t foggy or swampy, but it is only about 2km (a little over a mile) from the North Atlantic Ocean. Perhaps hard insulation over the inner cover doesn’t work so well this close to the ocean. I’m not convinced that’s the case, but it’s possible. In the end, it doesn’t matter. There’s a thin layer of mold covering all the comb in the top boxes and the frames feel cold and damp. To prevent it from getting worse, I’ve removed the hard insulation and added a moisture quilt. I’ve never seen anything keep the inside of a hive dry better than a moisture quilt, so to play it safe, the moisture quilt goes on.

My apologies for not being able to continue with the hard insulation experiment.