Guilfordbeekeepers.org

Both my hives have screen bottoms but allow for a board to be slid in for mite counts and I presume protection from the cold in the approaching winter. When should I put the bottom boards in to protect the bees from the cold?

Runner963,
I also have screened bottom boards and only use the inserts for mite counts and when necessary for treatments.
Bees do not keep the entire hive warm, they only keep the cluster warm, so cold temperatures will not kill bees but moisture will.
Maintain good ventilation and an adequate wind break and you will not have to put the inserts in the bottom board.

As President Rob has posted numerous times:
Please put your location in your profile as all beekeeping is local.

I'm moving away from using screened bottom boards (except for mite counts) as a matter of personal preference, but I have left the screens open all winter a couple of years ago when we had cooler temperatures than the last two winters. The bees did fine over winter. My impression was that they did not move down into the bottom box as fully or as readily as they do with a solid bottom board.

Please do add your location to your profile. We welcome members from any location, but if you are in a very different weather location, the answers to certain questions may be different.

I have also noticed the past few years that the bees do not fully utilize the bottom of the frames in the bottom box when there is a screened bottom board except for this past season. This past season they filled everything, maybe it was the mild winter or the strong nectar flow.
I have heard some beekeepers used slatted racks with screened bottom boards and had the bees utilize the bottom of the frames so as an experiment I have added slatted racks to 4 hives to see if I can get the same results.