In any locality where the average temperature of the winter months
falls below 25° F. (zone 1) cellar wintering may be practiced with
profit, and in localities where the average temperature of these
months falls as low as 15° F. (zone 2) cellar wintering is much to
be preferred. Figure 1 shows the boundaries of these zones for the
United States for the month of January, which may be taken as typical
of the winter months. It will be noted that these zones do not follow
parallels of latitude. As was pointed out in the bulletin of the
department on outdoor wintering,[2] it is quite possible to protect
bees in zone 1 sufficiently to winter them outdoors, but if a proper
cellar is provided, if conditions within the cellar are correct, and if
the stores are good and the colonies are strong, just as good results
may be obtained from cellar wintering.
[2] Farmers' Bulletin 1012, Preparation of Bees for Outdoor Wintering.
In zone 1 the average temperature of the outside air during the mouth
of January is 25° F., or lower in the more northern parts of the zone.
This means that in colonies wintered outdoors the bees are compelled
to overcome this degree of cold at all times during the coldest part
of the winter. If they are so well packed that the heat which they
generate is lost slowly, they are able to generate sufficient heat to
make the interior of the hive warm enough to allow them to break their
cluster as is necessary. In zone 2, however, the bees will be compelled
to generate heat sufficient to overcome the more severe cold of that
zone, and this calls for the expenditure by the bees of so much more
food and vitality that it is more economical to put them in a good
cellar during the months of the most severe cold, and cellar wintering
is therefore preferable.