We are new to terrace gardening (we are on the 8th floor of a building at Bloor and Bathurst that faces east) and were curious about wintering our plants. We have four Royal holly plants in double walled planters and two Green Mountain boxwoods in formal square planters. We want everything to survive the winter and need to know what we should do. Should we wrap the plants and the planters in burlap? Suggestions on how to wrap them? Thank you for your help and assistance.
Growing shrubs in containers is a great idea for those with balconies but it does come with challenges, especially when trying to overwinter them. Your challenges will be cold temperatures on the 8th floor, winter chilling wind and the infamous freeze/thaw cycle. These challenges can lead to severely frost damaged roots and dry, parched, thirsty plants with browning/dropped leaves and/or dead branching.
Below you will find a short list of ways to help keep your Holly & Boxwoods stay alive:
- Relocating planters away from the balcony railing and situating them close to or up against the building exterior wall will provide more shelter from the wind. Many people also erect a screen shelter abutting the building wall, in effect creating a small protected corner for the pots.
- Containers also need insulating in order to keep roots inside the pot from severe frost damage. This insulation can be either Styrofoam home insulation sheets cut to fit around the exterior of the pots or straw bales which can be placed into large garbage bags – both of these options need to be secured firmly in place with twine, bungee cords or packing tape. The goal is to keep as much of the cold out so eliminating and cracks or crevice’s is important.
- Protection of the upper part of these plants is also important as they are both evergreens and will loose moisture through their leaves during sun exposure during the daytime hours. Building a teepee using stakes or poles and then wrapping that structure in burlap will help protect from wind and cold but will also help with moisture retention within the plant itself and the container soil.
- In Canada, most locations go through the “freeze/thaw” cycle every winter. This is where, during the day when temperatures are warmer, the top layer of soil thaws out and moisture is released to the plant roots, by evaporation or as run off. This moisture, in a garden setting would be replaced by sheer soil volume or by snowfall. In containers on a balcony, the soil volume is limited as is the snowfall, so regular watering of pots needs to be done in order to maintain moisture for plant roots. Watering pots well until freeze-up is key and then monitoring the weather/daily temperatures and watering with top-up’s every couple of weeks as needed.
I do hope this advice is helpful but before following it, I would urge you to read the rules and regulations pertaining to your building or check with the building management to see if there are limitations or restrictions.
September 19, 2021