Question
We planted cedar scrubs a few years ago and would like to know when and how do we trim them?

Answer
More than likely they do not need pruning right now.
Downsizing Cedars If a plant has grown too large, prune it down to size in the spring, before growth starts. Take special care not to remove too much growth from the outside of the plant at this time. On a typical cedar, there is green growth only on the outer 15-30 cm (6-12 in.) of each branch in the early spring. All conifers lose their oldest needles or leaves, which are towards the centre of the tree. If most of the green growth is pruned off the outer part of a branch, it will be left virtually bare. The virtually bare branch will seldom produce new growth and it will likely die.

Any amount of pruning to downsize a cedar will inevitably make it look somewhat unattractive until it has had a chance to fill in, which can take a few years.

In reducing the height of a cedar ("topping" it) do not prune excessively or the top of the plant may not fill in again and will look very unattractive. In topping a pyramidal cedar, it is recommended that you prune the main trunk back no more than about 1/4 of the tree's height. The tree will gradually fill in on top and continue growing up. If you must reduce the tree's height further, stake the top branches into an upright position so that the top will fill in. The year after a cedar is topped and in subsequent years, shear the new growth to keep the tree from getting too tall again.

For columnar cedars, follow the same topping procedure described above for each of the main trunks. Globe cedars will seldom fill in if they are topped excessively. Globe cedars that have been allowed to grow excessively large in width and height are difficult, if not impossible, to prune. It is vital to prune them regularly to keep them from growing too large.

Keeping Cedars in Shape To maintain a compact, thicker look for your cedars and to keep them from growing too large, shear the plants once a year, between mid-June and mid-July. If you want an even tighter, more manicured look, you can shear them twice or even three times during this period.

Avoid pruning after mid-July. By late summer, growth has ceased and the buds that will produce next year's growth have formed. Pruning must be done before these buds are formed. If you remove these buds, the plant will be forced to produce more buds. This will deplete the cedar's energy reserves and the plant will enter winter in a weakened state and be more susceptible to winter injury.

In pruning cedars, remove some but not all of the present year's growth. These are the green stems; the older stems are brown in color.

How much new growth should you prune away? That depends on how fast you want the tree or shrub to grow. If your cedar produces six inches of new growth each year, you can restrict its growth to only 1 inch per year by removing 5 inches of the new growth annually.