Answer: Container gardening year round on a balcony in a cold winter climate such as yours is always a challenge. The primary reason is that the roots are not as well insulated as they would be if grown in the ground, so they are not only subject to cold but also to oscillating soil temperatures. Both of these conditions are extremely stressful on the plants. You might try junipers, however they do need full sun (a minimum of six hours of direct sun including the hour of noon) to stay healthy. The more sheltered and less windy the spot, the better their chances. The larger the container, the better. You would want to plant them in the spring so they are well rooted by the time the cold weather arrives. Also make sure to keep the soil slightly damp (not saturated, just damp like a wrung out sponge) whenever it is not frozen. Finally, make sure your balcony can hold the weight of a large container of wet soil safely. In my experience, most of the container evergreens in your area, including in Manhattan, are replaced in March or so every year because they become very stressed over the winter months and look shabby by then. I'm sorry I can't be more encouraging.
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