Potted Emerald Cedars for Roof top Terrace?

(Question)

I am looking to build a privacy screen for the roof top terrace which needs about 15′ of cover.

I was wondering if I can grow 5′-6′ Emerald Cedars in container pots?  The containers I’m looking at are trough shaped 36″ x 20″ x 20″ in dimensions but they’re self watering, so their depth is only 13″.  I was planning to put 2 Cedars per container, so I’ll need 5 containers and 10 Cedars.

I’m afraid the container might be too small for the root system.  If I move them into individual containers, what do you think the minimum size pot?  15″x15″? 20″x20″?

Location is Toronto, ON, Canada.

(Answer)

Emerald cedars with their bright green, dense foliage and columnar shape are a good choice to provide screening and should do well in containers with some care.  While they will grow to 12 ft (3.65 m) when planted in the ground, the restricted size of a container will keep them closer to the size you are after.

Art Drysdale in his book “Gardening Off the Ground”, recommends containers for evergreens such as Emerald Cedar should have a minimum soil depth of 12 in (30 cm) with 16 in (40 cm) desirable.  The trough shaped containers you are considering are on the low end of this range.

Wind is a major consideration on a roof top terrace for many gardeners.  Wind is very drying and will topple over large plants that do not have a secure base. For these reasons, I recommend the 20″ x 20″ in (50 cm x 50 cm) containers.  You will need to provide some winter protection either by moving the containers to a more protected location or by wrapping?  If so, the individual containers will make this process easier.

Emerald cedars like to be kept moist so add lots of organic matter when planting and top with a layer of mulch.  You will need to water frequently, at least once a week and more often when the weather is hot and dry.  Keep watering in the fall, right up till the containers freeze.

Finally, Art notes that you should be sure to enquire on the guarantees offered by your garden centre supplier as some suppliers will not extend their usual guarantee for evergreens if they are grown in containers.