How to Prepare Balcony Planter Boxes for Winter

Now that the growing season is over, how do you prepare your planter boxes and growing containers for winter?   There a few issues to consider: container cracking, keeping your perennials alive, and soil loss.

Cracking: What Material is the Container Made Of?

  • Plastic
    • Plastic pots and self-watering containers generally overwinter well.  We live in an area where temperatures go negative and all our boxes have made it through winter without cracking.  Self-watering planter boxes usually have a drain hole, to get rid of any excess rain or snowmelt.
  • Terra-Cotta or Clay
    • These types of pots are subject to cracking from freeze-thaw cycles.  Water gets in the micropores of the clay, and when water freezes, it expands enough to cause stress in the material.  If you have clay or terra-cotta pots, it’s best to bring them indoors or to a dry sheltered area if you want to use them next season.

Perennials vs Annuals?

  • Annual Plants
    • Annual plants are meant to only live one season, so they will likely die during freezing winter conditions.  I tend to leave them in during the whole winter, even though they have died.  I think the dried plants have interesting shapes.  Also, their presence reduces wind across the soil, and their roots hold soil, reducing soil loss.  This is personal preference, of course.
  • Perennial Plants
    • Hardiness: Perennial plants are meant to last more than one season.  However overwintering in a planter box is harder on plants than if they were in a regular garden.  So when choosing balcony plants, try to select those that are hardier to colder conditions than where you live.
    • Pruning: Whether you should prune your perennials before winter varies by plant.  Some, like lavender, should usually be pruned prior to the winter, but others like salvia would be pruned in the spring.  So you need to look up the recommendation for your specific perennial plants.
    • Water: You don’t need to water as often as during the growing season, but you don’t want to have the boxes dry out for months if you want perennials to survive.  Even some snow on the planter box will some moisture for the plants.

Soil Loss: Are Conditions Windy?

Cold winter winds can blow away topsoil in your containers.  To reduce soil loss, you have few options:

  • Leave plants in place. 
    • Even dead plants will slow the wind across the soil, and roots will help hold soil.
  • Cover the soil.
    • You could use a planter box cover, they are available for EarthBoxes and City Pickers containers.  Use a plastic garbage bag or burlap, tied down well, for a home-made option.
  • Move the planter boxes
    • Wind speeds (and thus soil loss) will be worst near the edge of your balcony.  Conditions are more sheltered if you can move your containers near the building walls.

Our winters are cold, so we leave the plants in place, wrap our containers with burlap, and nestle the boxes them close to the side to the building.  Last year we didn’t prune our lavender before winter and it died; this year we are going to prune it and see if that makes a difference in its survival.