Should I wrap my beehive for winter?
The sources split. One extension guide tells you to wrap, another says to wrap if necessary, and an experienced beekeeper says it is helpful but not essential. This page sets the positions side by side, shows the one controlled trial I found, and collects the points all of them agree on about ventilation.
Four positions
| Source | Position | Detail |
|---|---|---|
| Cornell CALS | Wrap | Roofing paper cut to fit around the hive bodies with at least an 8 inch overlap, put on while daytime temperatures are still above 50°F (10°C). "Winter wrapping prevents bee-killing drafts." |
| University of Florida (Ellis and Hammons) | Wrap if necessary | For far northern states and Canada: wrap to reduce wind infiltration and to warm the hive on sunny days. Put the hive in a sunny spot, out of the wind. |
| Jim Withers on Honey Bee Suite (Michigan beekeeper) | Helpful but optional | He thinks wrapping is not necessary but is helpful. Strong colonies with enough stores can often winter without it. He uses 15 lb roofing felt for solar gain. |
| University of Illinois trial | Covers helped | Covered colonies lost mass about two times more slowly and had lower winter mortality. Details below. |
What the Illinois trial found
St Clair, Beach and Dolezal (University of Illinois Urbana-Champaign, PLoS ONE, 2022) split 43 full-size colonies across eight apiaries in Champaign County, Illinois (about 40°N) for the 2020 to 2021 winter. 22 got a 4 mm corrugated polypropylene cover with 1.5 inch foam insulation on top of the inner cover, and 21 were controls. All colonies had mouse guards and entrance reducers.
The covered colonies lost mass at a rate the authors describe as almost two-fold slower, and they ate less of the mid-winter sugar cake. The results section reports 4.8% mortality for covered colonies against 27.3% for controls. The discussion gives a slightly different control figure (28.6%, 6 colonies), so treat the numbers as approximate.
The authors also list limits. It was one winter in one temperate region, cluster temperatures did not differ overall, spring bee populations and brood did not differ, and all colonies were fed heavily in fall. Survival was judged by listening with a stethoscope. They say the mechanism was not directly tested. A winter in a place without extreme cold says little about Minnesota or Quebec, and the trial used a purpose-made cover, which a roofing paper wrap may or may not match.
What they agree on: do not seal it
- Cornell: "Ventilation is critical to survival of overwintering bees." Water condenses on cold surfaces, and "wet bees in cold weather will soon be dead bees."
- Cornell suggests a shim under the inner cover or a notch cut into it, and a small upper entrance as well as the lower one. When you add insulation above the inner cover, do not block the upper entrance.
- Florida: keep enough air flow to discourage moisture, by an upper entrance, an auger hole in the side of the top box or a ventilation rim.
- Withers: too much moisture in a wintering hive is a danger. Foam under the telescoping cover reduces condensation dripping onto the bees, and he recommends an upper entrance for moisture and for cleansing flights when snow blocks the bottom one.
- Cornell says entrances should face away from the prevailing wind, and not to worry if snow blocks the lower entrance.
My view
My suggestion: decide by wind and by cold, then check ventilation before you check anything else. An exposed apiary in a cold region is where the sources lean toward wrapping, and a sheltered hive in a mild winter is where Withers's "helpful but optional" fits. Whatever you choose, an open top vent matters more than the wrap itself, because Cornell, Florida and Withers all warn about moisture.
Wrapping may also change how much the colony eats. The Illinois mass numbers point that way, and your own check is a weight. Lift or weigh the hive with the hive weight page, then see how long that lasts in the winter stores run-out estimate. If the hive is light, the sugar guide shows what to feed before the weather turns.
Wrap on a mild day. Cornell puts the line at daytime temperatures above 50°F (10°C). A mouse guard goes on at the same visit, and the mouse guard page covers the timing.