An informal hedge contains a variety of shrubs that are allowed to grow and bloom in their natural shape. Prune these shrubs individually just as if they were planted separately.
A traditional cedar hedge is a good example of a formal hedge. This type of hedge requires much more maintenance than an informal one.
The ideal shape for a formal hedge is trapezoidal, wider at the base than the top. This allows sunlight to reach the base of the hedge and prevents it from becoming bare. It is also best to round the top, because a flat-topped hedge is more apt to be damaged by the weight of snow and ice.
When to prune?
Deciduous hedges may need to be pruned just once or several times a year, depending on how vigorously each species grows. Use pruning shears on the current year’s growth. The first pruning should normally be done in June, after the spring growth flush. The final pruning should be done before September.
Evergreen hedges do not usually require pruning more than once a year. Cedars and other random-branched species should be pruned in late June, once most of the current year’s growth is complete. They can be pruned anytime until early September, except during extremely hot or dry spells. Hedges containing whorl-branched conifers should be pruned in late spring, before the needles on the new shoots (candles) open.
You can use pruning shears to cut the new shoots by one- to two-thirds.
Never prune wood that is over two years old, because evergreens do not regenerate readily from old wood. You should also wait until the hedge has reached the desired height before pruning the top.
Illustrations: Espace pour la vie/Audrey Desaulniers