A Quick Course in Pruning Conifers
Pruning conifers or needled evergreens incorrectly can be disastrous to the appearance and health of your trees. To understand how evergreens should be pruned, you must know how and where they produce new growth. Needled evergreens fall into two basic groups which are determined by their branching pattern; whorl-branched and non-whorled or random branching.
Whorl-branched conifers branch only once a year when new growth occurs in the spring. This results in a whorled growth of branches at the growing tip. In this group, new growth comes from buds at the tips of the branches, buds along the new growth, and from buds at the base of the new growth. Evergreens that fall into this group should not be cut back beyond where there is green growth (or beyond the last whorl) because there are no latent or dormant buds in the bare old wood. If pruned back beyond this point, there will almost certainly be no regrowth on the branch and it will remain a bare stick.
Whorl-branched conifers include: Abies (Fir); Cedrus (Cedar); Cryptomeria; Larix (Larch); Picea (Spruce); Pinus (Pine)
Random branching conifers produce new growth from buds at the tips of the branches and also from buds that are randomly located along the stems. These evergreens have dormant buds and foliage further back on the stem than the whorled branched species. The result is that this group can be cut back harder and still break into new growth. Still, to be safe, you should not cut back beyond where there is green growth.
Non-whorled or random branching conifers include: Chamaecyparus (False cypress); Cupressus (Cypress); Cupressocyparis leylandii (Leyland Cypress);Tsuga (Hemlock); Juniperus (Juniper);Thuja (Arborvitae)
How to Prune Whorl-branched Conifers
These evergreens have a naturally beautiful shape and normally, they require little pruning. Care should be taken when a species or cultivar is chosen to select one that will not outgrow the space you plant it in. Growth can be controlled by pruning if you start when the plant is young. If you wait until the tree has outgrown its space, it will be too late to shorten the growth and have the plant look natural.
The new growing tips on whorl-branched evergreens are called candles. You can control the growth of your tree by pruning the candles. If you want to slow the growth a little but still want it to get bigger, remove about 1/2 to 1/3 of the candle when it has elongated to 2"-4" usually in mid to late spring or early summer. If you want the tree to remain the same size, remove the entire candle when it gets to be about an inch long.
Other selective pruning should be done in early spring so that the cut ends will heal quicker. Dormant buds behind the cuts will begin to grow and will hide the cut ends.
If pruning is done too late, these buds will remain dormant and no new growth will occur to hide the cut ends. Never cut back into bare stems. Always cut back to a side branch or a dormant bud so you will get regrowth.
How to Prune Random Branching Conifers
These evergreens can tolerate more pruning than the whorl-branched group because they have more dormant buds along the stem. Pruning cuts can be made almost anywhere along the stem except into bare wood. Pruning to maintain shape is best done in early spring so the new growth covers the cut ends. Selective hand pruning rather than shearing creates a more natural shape. Prune to remove wayward branches in early spring. Cut back to a side branch. To prune to maintain size shear the new growth in summer once the tree or shrub has stopped growing. For prostrate or open growing plants, it is often better to selectively prune individual branches rather than shearing the whole plant.
Keep in mind that for both of these types of conifers, dead, diseased, or damaged branches should be removed as soon as they are noticed regardless of the time of the year. When removing diseased portions, be sure to disinfect shears with a 10% bleach solution between cuts.
To avoid winter damage, do not prune evergreens in late summer or early fall. The tender new growth that forms will not have time to harden off before cold weather sets in and will freeze and turn brown.