Thujas and yews respond well to sever cutting back. Old plants may be reduced by half, and lateral branches should be shortened by half or a third, so as to shape the hedge into a sloping form. Dead branches should be removed. The best time to rejuvenate conifers is summer, from the beginning of June to midsummer. You could also prune in the second half of summer to early winter, however, this period is less favorable. The rejuvenated plants should be looked after, fertilized, and watered in a prolonged dry spell.
Although thujas are an exceptionally die-hard genus, it is only next year that the hedge will start breaking into new growth. Thujas need a lot of sunlight, and they will turn spindly when planted in a shaded position, while yews can take some shade very well. The yew or thuja hedge can be sheared in early spring, or (and) several times during the summer. In order to keep the hedge dense, the tops and the sides of the plants should be trimmed regularly.
In regard to how well conifers take to shearing, junipers fall somewhere in between the yew or the thuja and the conifers of the pine family. While junipers do not take kindly to severe cutting back as thujas would, they respond well to regular trimming, especially Juniperus x media, Juniperus squamata or Juniper virginiana.
One should not even attempt to rejuvenate a hedge of hemlocks, spruces, firs or pines, since these conifers do not break into new growth from old wood. Therefore, it is important that hedges of these conifers should receive regular maintenance right from the beginning. A hedge should be trimmed every year, so as to avoid any die-back of branches. Best time to clip these plants is the summer (June to July), when the weather is warm and dry. Alternatively, pruning could be done in late winter or early spring, but this is less favorable time. Refrain from clipping conifers of these genuses in April and May, after the plants break dormancy, since the conifers will “bleed” too much sap and the wound will take time to heal, which will weaken the plants as a result.
One way of trimming conifers is to nip terminal shoots, leaving only lateral ones. This is an efficient way to keep the hedge in check, albeit one requiring a lot of time and patience. Alternatively, you could cut back young new shoots, which will reduce the growth rate of the hedge, ensuring its compact form and preventing any dead branches. Make sure, that there are still several lateral shoots to cover up the removed terminal shoot. This task is best performed in summer, however, it can be done any other time, provided you do not cut into old wood, and the tree does not loose too much sap. The shoots of pines have no lateral buds, therefore the cut should be made as close to side shoots as possible, so as to prevent dry stumps of cut branches sticking out.
© Giedra Bartas, 2010