Canadian winters kill more hives than any pest. The good news: most overwintering deaths are preventable with decent preparation in September-October. This guide covers the four killers — starvation, moisture, cold, and varroa — and what to do about each, specifically for climates from BC's coast to the prairies to Atlantic Canada.
The four winter killers
Starvation. Hives need 60-80 lbs of stored honey in southern Canada, 80-100 lbs in the prairies and north. If you're unsure, heft the hive. If you can lift the back with one hand, it's too light and you need to feed.
Moisture. Bees generate moisture as they respire. If moisture can't escape, it condenses on the inner cover and drips back onto the cluster — a faster killer than cold. Proper ventilation is non-negotiable.
Cold. Bees cluster at -10°C and below. The cluster heats its centre but not the hive volume. Big empty space above the cluster wastes heat; extra insulation above it preserves it.
Varroa. A hive with mite loads over 3% in September enters winter already stressed. Going in with low mites is the single biggest driver of spring survival.
Fall checklist (September-October)
- Treat for varroa. Formic acid, oxalic acid, or Apivar — your choice based on climate. Apply before winter bees are raised so they emerge mite-light.
- Assess food stores. If light, feed 2:1 sugar syrup while temperatures are above 10°C (bees can still process it). Below 10°C, feed dry fondant or sugar bricks on top of the frames.
- Combine weak colonies. Two weak hives going into winter die. One combined strong hive survives. Ruthless now is kindness later.
- Reduce entrance. Use a mouse guard — metal, not plastic — and reduce the entrance to cluster-width.
- Re-queen if necessary. Queens over 2 years old are at higher winter-failure risk.
Winter wrap (November)
- Wrap the hive with insulation. Black-coated insulation absorbs solar heat. On the prairies, 2 inches of foam on top of the inner cover plus a full wrap is standard. In milder BC coastal climates, lighter wrap works.
- Upper entrance / ventilation. Drill or prop a 1 cm gap at the top of the hive so moisture escapes. Seal the bottom entrance partially with the mouse guard.
- Windbreak. If your hive site is exposed, stack straw bales on the prevailing-wind side. Wind steals heat faster than cold temperature alone.
- Tilt slightly forward. 2-3° forward tilt lets condensation drip out the front entrance instead of pooling inside.
Winter checks (January-February)
- Do NOT open the hive when it's below 5°C.
- Listen at the entrance on a still day — a faint hum means they're alive.
- Check food weight by gently tilting the hive. Top up with fondant on the inner-cover opening if it feels light.
- Clear dead bees from the entrance weekly — a clogged entrance suffocates them.
FAQ
Do I need to wrap in southern BC?
Light wrap or none. The bigger issue on the coast is moisture from constant rain — ventilation matters more than insulation.
Can I feed through winter?
Only with dry fondant or sugar bricks placed directly above the cluster. Syrup freezes and can't be processed.
How much varroa mortality is "normal"?
Zero is the target. A colony going into winter with under 1% mite load has a strong chance of survival. Over 3% is a red flag.
