>>I am in a real dither about covering  the screens or not.

I am east of you.  I place a sheet of 1" white styrofoam (reclycled packing material) under the screened bottom boards to block drafts.  Top ventilation & insulation is provided (a critical element) to prevent water condensation in the hives.  The entrance reducer opening is left open 3-4" wide x 1/4" high in the center to supply fresh air.

I have not head any problems with moisture or mold since I've gone to this set-up.

Strong colonies with great stores will survive winters with the open screened bottoms but they will consume a lot more to keep the cluster alive.  Colonies with smaller bee numbers and/or stores are likely to suffer a cold death.

>>I find a real split between those who are afraid of drafts (cold being the worst enemy) and hence cover them and those who leave them open (dampness being the real enemy). 

It's best to ask the bees. :)  In the wild, they don't like drafts but have a top vent of some sort even if it's just dry rotten wood overhead in a tree.

Moisture and wet cold are a killer.  Especially if the hives are fed late and the bees are still trying to evaporate water from the syrup after temps drop.

Waldemar

What do you advise?
John Howe

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