Conifers, like most trees, can benefit from some pruning. Tree trimming requirements are a bit different for conifers compared to deciduous trees, so it's important to know the basics.
Most conifers are best pruned during the active growing season. This means that it's necessary to wait until new growth begins to appear in spring. Once new growth appears, usually in the form of young tips at the end of branches, it's pruning season. You can safely prune a conifer at any point from spring through late summer.
While the above seasons are correct for conifers like pines, spruces, and firs, there is an exception. You may be able to prune some yews fall, as long as it is before the first freeze begins to put the tree into partial dormancy. This provides a longer pruning season, spring through fall, for yew trees.
Trimming is primarily a health practice with conifer trees. The majority of species maintain an attractive natural form quite well, so they rarely require any pruning for shaping. Instead, pruning is done to remove dead or damaged wood, or it may be done to thin out an especially dense tree.
When you're cutting to remove damaged wood, remove the branch back to where it joins the nearest healthy wood or the trunk. You may also need to remove scrubby, weak stems along the bottom part of the trunk, below the main canopy. Do this by cutting the weak branches off flush to the trunk. If the crown is dense with poor airflow, you can also trim out roughly a quarter of the branches inside to open up the canopy. Focus on the removal of crossed branches or those with weak angles to the trunk, cutting them out as you would damaged wood.
Issues and Concerns
One issue with conifers is that they will not produce new needles further back on the branch. If you decide to prune back some branches without removing them completely, perhaps to control height or length, then avoid cutting back beyond the last of the needles before the trunk. Otherwise you will end up with bare branches and bald spots in your tree.
Further, keep in mind that cutting off the growing tip of the branch will prevent it from putting on any more growth from the end. Only trim off the end of a branch if it is at the desired length and you don't want it to grow any longer.
Contact a tree trimming service in your area if you need more help with the conifers in your yard.