You need to protect potted blueberries winter since container roots freeze faster than in-ground plants. The pot sits above ground where cold air hits it from all sides. Your goal is to keep roots from hitting below 20°F (-7°C) for long stretches.
I tried several methods over the years to see what works best. Moving pots into my unheated garage kept them safe through two harsh winters. Leaving them outside with just mulch worked fine in milder years but cost me one plant during a cold snap.
When I first started winterizing container blueberries, I wrapped the pots in burlap and hoped for the best. That helped a bit but wasn't enough when temps dropped below 10°F (-12°C) for several nights in a row.
Container plants face more cold risk because soil in pots lacks the mass of ground soil. In-ground plants have feet of dirt around their roots that stays warmer. Your pot roots sit in just a few inches of mix with cold air on every side.
Potted blueberries need shelter from December through March in most zones. Experts agree on this window. Cold protection blueberry pots need depends on your climate and zone.
Wisconsin Extension suggests piling 4 to 8 inches of straw mulch around and over your containers. This traps air and slows heat loss from the soil. Stack bales around the pots for extra shelter in exposed spots.
Move your containers to an unheated garage or shed if you live in zones 3 through 5. The walls block wind and keep temps above the danger zone. Just don't put them in a heated space since blueberries need winter chill to fruit next year.
Growers in zones 5 through 7 can often leave pots outside with good cold protection blueberry pots get from wrapping and mulching. Group containers together and push them against a south-facing wall. The wall reflects heat and blocks north winds.
Zone 8 and warmer areas need little winter care for blueberries. A light mulch layer over the soil surface is enough. Your bigger worry is making sure the plants get enough chill hours to set fruit.
Check soil moisture every few weeks during winter. Roots can dry out even when dormant. Water lightly on warm days when the soil thaws. Soggy soil is bad, but bone dry kills roots just as fast.
Start winterizing container blueberries in late fall before the first hard freeze hits. Move pots into shelter or add mulch while the weather still lets you work outside. Rushed prep in freezing rain makes the job miserable.
Read the full article: How to Grow Blueberries in Pots Successfully
