I received several emails with concerns about what kind of care container trees require, to get them through the winter. Some of the emails were from folks in apartments and their potted trees were also exposed to high winds; a double whammy.
Over-wintering containers takes some experimentation. There are several things to take into account, when growing trees in containers, no matter where you live. First, choose a tree suited to your growing conditions, whether it is sunny, shady, wet or dry. Make sure the tree is hardy to a couple of zones below your USDA hardiness rating. That way it should be able to handle winter temperatures, even though it is above the frost line.
Some less obvious problems include how much to water and too much winter sun. Strong southern exposure sunlight can cause trunks and branches to freeze, thaw and eventually crack, during winter. As for watering, most trees will be dormant during cold winters, so they will need less water. Don't leave them dry for weeks at a time, but do not let them sit in wet soil, or the roots will rot.
Assuming your tree is hardy enough to be outdoors, the biggest consideration will be wind burn and desiccation. You can use burlap to shield the tree, but only consider this in extreme cases. Trees need sunlight, even in winter. If you do need to wrap the tree, don't let the burlap touch the branches and freeze to them. Use some sort of framing to keep a few inches between tree and fabric. A better idea would be to group several plants together and move them to a less windy location for the winter. There are also some good anti-desiccation sprays on the market.
If you are growing several trees as a privacy screen and you won't be able to do much protecting, take extra care in choosing rugged trees, like yew, juniper and viburnum.
And if you've had good luck overwintering a potted tree outdoors, let us know your tips for survival.
Photo: © Marie Iannotti (Taken at Iseli Nursery)