Will Cannas Overwinter in Zone 6?

Zone 6

• Average annual winter minimum temperatures in USDA zone 6 drop into the range of minus 10 to 0 degrees Fahrenheit. Topsoil freezes solid to varying depths depending on the duration of subfreezing temperatures from late fall to late winter. Presence of a snow cover or a deep mulch layer over the soil may limit the extend of frost downward into the soil. Gardeners in nearby Zone 7 have limited success overwintering cannas outdoors over their slightly milder winter temperatures with a mulch layer. Zone 6 gardeners will not have success overwintering cannas outdoors in the soil, even with protective mulch or snow cover.

Microclimates

• There is a slightly possibility that canna rhizomes left in the soil over the winter months in zone 6 may survive. It all depends on air and soil temperatures. A microclimate -- a localized area within the yard where warmer winter temperatures occur -- may increase the chances of overwintering cannas outdoors in zone 6. This microclimate, coupled with a 6- to 12-inch layer of mulch may cause some rhizomes to escape death from freezing. The southern side of a building foundation or wall, shielded from wind, offers the warmest winter conditions in zone 6.

Recommendations

• Winters in Zone 6 are too long and cold to leave canna rhizomes outdoors in the garden. While a freakishly mild winter or lucky microclimate position may cause some cannas to overwinter, it's best to dig up canna rhizomes in the fall and overwinter them indoors in a cool, dry space. Wait until the first fall frosts kill back the aboveground leaves and stems and then cut back the stems to stubs 3 to 4 inches tall. Lift the rhizomes with a potato fork or shovel, removing soil and store them inside until next spring.

Overwintering Tips

• The ideal indoor location for storing canna rhizomes over the winter is between 40 and 50 degrees Fahrenheit. You may nestle the dry, undamaged rhizomes in barely damp peat moss, but do not keep the rhizomes in contact with anything soggy or wet. Wet conditions cause rot and fungal infestations. Check the rhizomes in mid- and late winter -- every four to six weeks -- to evaluate their health. Rhizomes that dry and shrivel up or display soggy or moldy tissues need to be discarded. Add a small amount of water to keep the media around the stored rhizomes barely moist the rest of winter.