Many junipers and other coniferous evergreens don't respond well to heavy or hard pruning. That being said, most can be lightly pruned for shaping with no damage to the plant. To avoid ever having to prune conifers, choose varieties that won't outgrow the space you intend to fill.
Pruning Junipers
When to Prune
Since junipers and other conifers produce new growth in spring and fall, and do not grow much in summer, prune them in early spring in warm regions or early summer in cooler regions. The only exception to this rule is pines, which should be pruned before the candle growth develops in the spring.
How to Prune Junipers
With the exception of topiary, which is the method frequent trimming to a formal shape: spiral, poodle tier or pompom, prune other conifers according to their growth habits. Low growing junipers used as groundcover rarely if ever require pruning, maybe just around the edges to keep them in bounds.
When pruning a conifer, it is a matter of cutting the branches so that a more desirable plant is attained through compact, controlled growth, while leaving the natural shape of the plant. This requires selective pruning of individual stems rather than indiscriminately shearing with hedge trimmers. Shearing not only ruins the natural growth habit but prevents light from penetrating into the center of the plant resulting in foliage drop.
Important Note: When pruning any conifer do not cut into bare wood beyond the foliage on the tips of the stems. Since few leaf buds are formed on older branches or stems, the plants may be damaged beyond repair if you cut too far back to the point of bare stem.
There are certain general rules to follow for various types of conifers:
Start pruning when plants are small, usually the first year after they come from the nursery. Then, if they are pruned a little each year, severe pruning, which can harm conifers, is not necessary.
Remove dead branches whenever they occur. New foliage from surrounding branches will usually fill in these gaps.
Pruning methods for various types of conifers:
Upright Spreading Forms
Upright spreading forms of junipers are those that typically grow 3 feet or more in height with a spreading growth habit. The tips of branches can be pruned each year to keep plants in check and induces a smaller, more compact plant. That said, if you provide enough space for a juniper to grow to it's mature size, no pruning is necessary.
An example of a vigorous-growing, spreading evergreen is Grey Owl Juniper. It is common for this plant to grow 12 inches or more in height and width each year. To maintain the natural shape of this plant, it is necessary to cut back to growing points and remove a single stray branch hear or there. It also may be necessary to cut back into the previous year's wood to maintain the plant's size and shape.
Upright Pines, Junipers and Other Conifers
Upright conifers are typically taller growing species or cultivars with a conical, pyramidal, pillar-like or upright rounded habit of growth, such as many cypress, junipers, pines and cedars. Little if any pruning is required for these species. Damaged or dead branches should be removed when they appear. Cut damaged branches off just beyond the break. Remove dead branches at their origin.
If you don't want to destroy the natural shape of upright growing conifer, do not cut the central leader (top vertical branch), except to remove a multiple leader. This may occur when the plants are young. Remove all but one of the leaders, leaving the straightest and strongest.
When pines are young and growing vigorously, the top growing point may outdistance the rest of the plant, resulting in an open space between the main body of the plants foliage and the growing tip. To encourage the plant to branch and be more compact, cut the top back to a dormant bud located near the main body of the plant. If this cutting back is done when the plants are young, there is little effect on plant appearance.
Spruce
Spruce require little if any pruning. If an entire branch has died cut it back to it's point of origin. Make the cut at a 45-degree angle just outside the branch collar; the slightly enlarged area where the branch joins the trunk or another branch.
Damaged or diseased branches should be cut back to a point beyond the break or disease. Make your cut 1 inch beyond a bud or healthy leaf. If you have to cut past where there is no needle growth you might as well remove the entire branch because it will not produce new growth.
To shape or control size you can lightly trim spruce. Trim the tips of new growth 1 inch outside a bud with pruning shears to encourage new side shoots and create fuller spruce trees. Do not trim growth older than the current season, and do not remove more than one-third of the new-season growth at one time.
Prostrate, Groundcover Junipers
If plants were given ample room to grow when planted, no pruning should be necessary on low-growing junipers used as a groundcover, such as Bar Harbor Juniper. That said, if and when they spread beyond their boundaries; over driveways, sidewalks or into the lawn, pruning may be necessary to keep plants in bounds. When this happens, simply use hand pruners or hedge clippers or trimmers to prune or edge them back.
TIP: When planting groundcover juniper near a walkway, driveway or other surface area where there will be foot or other traffic, it's best to choose the lowest growing variety you can find. Matt-forming junipers, such as Blue Rug Juniper, are much easier to prune or edge. Too, when they are pruned around the edges, the mat-forming junipers don't leave an unsightly "wall"of brown stem-ends. It's best to use wide-spreading, taller groundcover junipers, which grow taller than 6 inches in height, such as Blue Pacific Juniper and Parsons Juniper, for larger spaces or embankments where their foliage will not encroach on surfaced areas.