Plants in containers are more vulnerable to the elements because their roots are less protected with far less soil to blanket them. And then terraces increase that vulnerability, with greater wind exposure than a plant would get at ground level. All of these plants need to experience the cold weather as part of their annual cycle but you are right to be planning to give them some extra protection.

The particular type of each of these plants makes a difference - some are hardier than others. In general, azaleas will be the most tender in this trio of plants and need the most help. If your azalea is a deciduous one, it will be slightly more winter-safe. Even a hardier type of azalea, however, will be more at risk than the other plants and should take priority in protection from wind and cold. The containers and position on the balcony mean that your shrubs are experiencing conditions 2 or more USDA zones colder than your actual zone.

Evergreen plants will need to continue to receive water right up until the point that the ground freezes because they are still photosynthesizing. As temperatures drop, create a barrier of burlap around the perimeter of the planting area to break the wind which is the greatest threat to your plants winter safety. Often a sheet of burlap tied to the balcony railing works well and is far better than wrapping the individual plants. When the temperature gets into the 40's, pull the plants, especially the azalea, as close to the wall of your home as possible, where some extra warmth and protection occur. You can give each plant a topping of shredded bark mulch on the soil (keep a gap between stem and mulch) and wrap the pot in an insulating material (bubble wrap works as does wire mesh filled with leaves).

If the plant containers are made of terracotta or ceramic, they may crack if left outdoors during the winter. Plastic or metal is less at risk when fluctuating temperatures expand and contract water in the soil. If necessary, you may need to transplant the shrubs for the winter to protect their containers.

As winter progresses, keep your eye on the temperature. If we are getting a snap of severe weather dipping into the freeze zone, more protection may be needed for the azalea temporarily. Most rhododendrons and hollies will be fine with a wind barrier and some pot insulation in typical New York area winter weather conditions. If your balcony is very wind or weather exposed or winter weather is unusually severe, they may need a little extra help. Going forward, you will find that the hardier plants will be easier to get through the winter with less worry and fuss.

Courtesy of NYBG Plant Information Service