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.

Do You Need a Cover For a Self-Watering Planter?

A planter box cover is a flat piece of plastic or fabric, often with elastic edges.  They are sometimes called “mulch covers”.  They fit snugly over the top of a planter and you cut holes to allow the plants to poke through.

When we got my first City Picker self-watering planter, we didn’t use a cover.  This year, with two new EarthBox planters, we decided to use covers, to see how they worked.  Now that the growing season is over, I wanted to share experiences on using planter boxes with and without a cover.

Cover Pros:

  • Warm or cool the soil
    • EarthBox covers are neat in this way.  One side of the cover is white, the other is black.  You can have the black side up in springtime, which will absorb more sunshine and warmth.  This is great for starting seeds early.  In summer, you keep the white side up and that reflects the sun, allowing plant roots to stay cooler in the hot sun.  The City Picker cover is black on both sides, I believe.
  • Reduce evaporation
    • If you live in a dry climate that doesn’t get much rain, this is a great feature.  The cover keeps more water in the soil and reservoir, by being a barrier to water loss from evaporation.
  • Retain soil and fertilizer
    • If you live in a windy climate, a cover can reduce soil loss.  Our general area is not windy, but since our balcony garden is up high, it does get a fair amount of wind.  At the end of a season, we might need to replace about 1” of soil in a box without a cover.

Cover Cons:

  • Repel rain water
    • Very little rain gets through an EarthBox plastic planter cover.  This was the biggest disadvantage for us.  We live in a temperate climate that gets rain at least once a week in summer.  After a rainfall, my uncovered planter boxes would get their reservoirs filled and soil soaked.  The covered boxes stayed dry, waiting for me to water.  The City Picker cover is fabric, so perhaps that may let some rain through.
  • Not beautiful
    • I found the covers to be kind of ugly, though that is a personal preference.  I couldn’t get past the feeling that I was looking at garbage bags on top of my planters.

The EarthBox literature says that other pros of the covers are that they deter insects from burrowing into the soil and reduce weeds.  I’m not sure I found these to be true for my planters.  There were enough holes in the cover (for the plants), that insects could easily get under.  Weeds were not an issue in any of my planter boxes either with or without covers.

The decision on whether or not you need a planter box cover comes down to personal preference and climate.  For example, if you live in a dry, windy, hot climate, then planter covers will make more sense.  If you live in an area where you get regular rainfall and don’t have wind issues, then covers are only optional.

For us, we will likely cover our planters in spring, to help seeds stay warm and get an early start.  But in summer, we’ll take off the covers so that rain can get in.  We may look into a more traditional mulch, like perhaps gravel or wood chips and will report back on those options.