Marin Master Gardeners
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Marin Master Gardeners

Marin IJ Articles

How and when to prune a conifer

December 22, 2018
Anne-Marie Walker

“Prune a conifer?” you ask. Well, as Dylan Thomas said, we need “to begin at the beginning.”

Conifers are cone-bearing trees that produce tiny pollen cones in spring followed later by more substantial woody seed cones whose scales each contain two or more seeds. Generally, pine trees begin to produce viable cones within five to 10 years of age, cedars after 75 years and redwoods only after 200 years. The cones of all conifers hang down save for firs whose cones stand up. Needle patterns of conifers vary as well, with spruce needles stiff and sharp, while fir needles are flexible and friendly.

Many consider California’s coniferous forests unrivaled. Renowned English botanist Sir John Hooker once told John Muir that California’s forests surpassed all others around the world in beauty, grandeur, number and variety of species.

In Marin we find pines, firs, spruce, Douglas-fir and coast redwood on the slopes of Mount Tamalpais. Learning about different attributes of conifers — including tree shape, bark pattern, leaf and cones — helps us select, care for and manage conifers in our gardens. When we plant conifers in our home landscapes, we often need to prune for shape, health and removal of damaged limbs. Sometimes, when disease strikes, we need to cut out dead patches that might otherwise provide a host for fungal rots. Pruning also helps maintain height and defensible space; remember conifers are resinous and should be kept away from structures.

Generally speaking, conifers have a strong, dominant leader producing a conical shape that requires minimal pruning. The perfect example of a straight Christmas tree-shaped conifer is the Douglas-fir. The hyphen in the name indicates it is not a “true” fir but rather its own genus, Pseudotsuga, which translates to “false hemlock.” You can readily identify Douglas-fir by its vibrant new needles protruding from the twig.

Four basic cuts

To prune conifers, we use four basic pruning cuts; thinning, heading, shearing and pinching. To thin, remove an entire branch back to the trunk or parent branch. Thinning helps direct growth, reduce size, permit light into the center of the tree and remove old stems. Heading removes just part of a stem or branch stimulating vigorous new growth below the cut. This cut reduces wind resistance and can achieve aesthetic effect. Shearing heads a tree creating a flat surface hedge. Pinching, the fourth and simplest technique, cuts off the terminal bud forcing the shoot to branch.

The best time to prune conifers varies on when they grow. Spruce, firs and Douglas-firs are best pruned in late winter before growth begins in spring. Pines seldom need pruning and produce branches in whorls. You can thicken tip growth by pinching back the new growth by up to half in early spring. Remove dead wood then as well. Junipers, yews, redwood and cypress are all random branching conifers that grow continuously during the growing season. They should be checked and pruned in late summer before winter rains. This is especially the case with cypress, whose branches become unstable as they fill with rainwater and get buffeted by strong winds.

Conifers are beautiful and amazing trees. They can survive in snow and ice for months at a time by “hardening off” as hours of light decrease, a process that concentrates sugars, proteins and acids in the cells of trees to ward off the killing damage of freezing.

Remember to keep conifers watered once a month to a depth of at least 12 inches; about 10 gallons for each inch of trunk diameter. You will be rewarded and privileged to have nurtured trees of ancient origin.

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