Popular with amateur gardeners, thuja are most often limited in their use to the formation of tight and dense hedges. However, this tree of the cupressaceae family, with evergreen, is perfectly unsuitable for this use. Thuja, as we know it under its variety Thuja Occidentalis is native to Canada. It is not a shrub, but a real tree which, under normal conditions, can reach 20 m in height. A venerable size but which remains far from that of its cousin Thuya Plicata, originally from the West Coast of the United States, which can exceed 50 m high! The fashion for alignments of thuja dear to our suburban gardens comes from the rusticity of these, and especially from the low cost of their reproduction. The thuja is easily cut, and the nurserymen were not mistaken in offering gardeners plants at low production costs, therefore at low prices. In addition, thuja is easily pruned and adapts perfectly to a severe pruning which will give birth in less than a year to new green shoots. However, thuja will only be really beautiful when used alone. Its conical shape and its evergreen leaves make it a magnificent subject in the center of a lawn. Used as a hedge, sooner or later it will need to be uprooted. Although kept at 2 m in height, often half the width, the diameter of its trunk will continue to grow.
Cedar, a poisonous tree
Despite all these qualities, thuja remains a toxic plant where birds and insects - apart from the red spiders and the bupreste which are predators - are not welcome. The essential oil extracted from thuja is similar to that of absinthe. Its active ingredient consists of terpene, called thujone, which turns out to be a violent poison for domestic animals. Its absorption resulting in dog colic and severe diarrhea progressing to death. The use of cedar in close alignment for which it is not made, makes it subject to the appearance of parasites such as bupreste or phytophthora which can make its maintenance expensive.