Will a Black Lace elderberry survive in a 2:2′ styrofoam insulated container on a 3rd floor deck? The container is in a mostly sunny location.
Plants grown in containers on a terrace or balcony are more exposed to drying winds and to more extreme temperatures than plants in a garden. Therefore as a rule of thumb the growing zone on a balcony should be considered 2 zones below the zone of the area.
Most Black Lace elderberry cultivars, Sambucus nigra cvs., are hardy to zone 4 and would be an appropriate plant to grow on a terrace situated in hardiness zone 6a, as is Toronto. Their light requirements are full sun to part shade.
In addition to a good size container (the more soil, the better the roots are protected from freezing temperatures and from drying out) which is well insulated, regular watering right up to the time when the soil starts freezing and the application of a balanced fertilizer every 7-10 days will further help to grow the elderberry successfully.