The ideal time to prune a cedar hedge is at the end of June, after the flowering of the lilacs. At this point, its growth of the year is almost completed, but the new shoots are still of a lighter green than the stems of the previous year. And that’s important, because ideally you will only cut in the shoots of the year. You may also cut later in the season until early September, but then it is difficult to distinguish between young shoots and older ones, young people having lost their distinctive color.
By trimming, your goal is to remove one third to two thirds of the length of new shoots. You can work with a hedge shears (manual) or an electric hedge trimmer.
To draw a perfect line (still too precise for lazy gardeners!), Attach a stake to each end of the hedge, tie a rope to the desired height and adjust with a level. Just follow the rope with the shears … without cutting it of course.
Style to cut
For a beautiful hedge that will remain green from bottom to top and, moreover, can bear the weight of the snow, it is better to give it a trapezium shape, that is to say with a base wider than the top. Thus, the bottom of the hedge will receive its share of the sun and will not become unbearable. And the top must be rounded or pyramidal, as a flat top tends to open under the weight of snow or ice.
To slightly cut a cedar hedge
Ideally, you will control the height of a cedar hedge by an annual size, always remaining in the growth of the year. On the other hand, if your hedge has been neglected (a little), it is possible to slightly reduce its height and width by cutting more severely, but still remaining in the green part. Never cut into wood that is more than two years old, where there are no more green shoots, because the cedar regenerates with difficulty from the old wood.
Cutting apart a hedge
If for whatever reason you decide that you no longer want a cedar hedge then you can dispose of it by first cutting it down with a chainsaw. Then you can use a table saw like these (http://thesawcritic.com) to cut it up further so it can be either burned or taken to the dump.
How to Recover a Neglected Hedge
When you cut into the old wood, the hedge will not grow back. If your cedar hedge has become too large or too high (which happens quickly if you neglect to trim it annually), it will probably not be possible to recover it properly. Unlike a hedge of deciduous shrubs, which can be folded down almost to the ground and still be well rejected, if you cut in the old wood of a hedge of cedar, any regrowth, if there are (and it may have some branches still green), will be irregular, leaving you with a stripped top and walls full of dead sections for many years. Better to tear it out and start over.
One can however shorten a hedge too high (but not make it thinner) with some success … and a lot of patience! To attempt this experiment, fold the hedge to a height lower than desired, which will leave a top dead at the beginning. However, if you trim the lateral regrowth smoothly every year, always in the green, leaving the hedge to gain about 5 cm in height per year, this will encourage them to grow more and more towards the bare center. So, after several years, the damage at the top of the hedge will close, leaving you with an acceptable hedge.